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Screening of site-wide retrofit options for the minimization of CO2 emissions in process industries
Applied Thermal Engineering 90 (2015) 335e344
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Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng
Research paper
Screening of site-wide retrofit options for the minimization of CO2 emissions in process industries Kwang-Joon Min, Michael Binns, Se-Young Oh, Hyun-Young Cha, Jin-Kuk Kim*, Yeong-Koo Yeo Department of Chemical Engineering, Hanyang University, 222 Wangshimni-ro, Seongdong-gu, Seoul, 133-791, Republic of Korea
h i g h l i g h t s Systematic screening of retrofit options for the minimization of CO2 emissions. A holistic view considering multiple sources of CO2 and multiple retrofit options. Graphical methods to suggest the most cost-effective combinations of retrofits.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 March 2015 Accepted 4 July 2015 Available online 13 July 2015
This paper addresses the systematic screening of possible retrofit options for the minimization of CO2 emissions from process industries. In retrofit scenarios there are various options for the reduction of CO2 emitted which can be considered with different costs and capacities for CO2 reduction/removal. This study considers a holistic view accounting for multiple sources of CO2 emitted from a site and multiple potential retrofit options which can be implemented individually or in combination to meet CO2 reduction targets. For a given site the different possible retrofit options are ranked in terms of costeffectiveness and the most appropriate options are highlighted using graphical methods to suggest the most cost-effective combinations of retrofits. A case study is used to demonstrate the applicability of the proposed design methodology. This case study illustrates how fuel switching and energy-saving projects can be practical and beneficial measures for the implementation of decarbonization in process industries. © 2015 Elsevier Ltd. All rights reserved.
Keywords: CO2 capture Retrofit Energy savings Fuel switching Process design
1. Introduction Industrial plants such as refineries and petrochemical plants etc. emit flue gases from various sources with different CO2 compositions and flow rates. These sources of CO2 emissions will typically be found at different locations in the plant unlike conventional power plants which will generally have just a single source of CO2 emissions (flue gas from the combustion units). The reduction of CO2 emissions can be achieved through various different methods. These methods can be divided into three different categories:
* Corresponding author. Tel.: þ82 2 2220 2331. E-mail address: [email protected] (J.-K. Kim). http://dx.doi.org/10.1016/j.applthermaleng.2015.07.008 1359-4311/© 2015 Elsevier Ltd. All rights reserved.
1) Process modification 2) Energy systems modification 3) CO2 capture Modifications applied to the processes or to the energy systems are generally aimed at reducing the energy consumption (and also costs) which lead to the indirect reduction of CO2 emissions for example due to reduced fuel consumption. Alternatively CO2 capture involves the direct extraction and removal of the generated CO2 (e.g. from emitted flue gases). The implemented modifications are limited by a number of constraints when considering the retrofit of an existing site. Possibly the most important constraints are the upper limits placed on capital investment required to purchase new equipment but also there may be practical engineering constraints (e.g. limited space for equipment and for gathering/ducting flue gases due to the plant layout).
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Hence, CO2 capture and process/energy system modifications requiring additional equipment may be considered unfavorable due to the investment costs required. The most desirable options are energy-saving retrofit projects without any process modifications or additional capital investment required on the site. One such example of this type of ideal retrofit project is the energy-saving achieved through operational optimization of site utility systems. However, in terms of the total site-wide CO2 reduction the impact of this single retrofit option may not be significant and so a retrofit including multiple different modifications should be considered to achieve a more substantial reduction of CO2 emissions. When considering the modification of energy systems heat integration techniques can be applied to assess theoretical potential energy savings in the plant with the aid of energy targeting tools [1e3], network pinch methods [4] or superstructure-based optimization methods [5] which can identify options giving the greatest reduction of energy consumption. In addition studies have also been carried out linking the improvement of energy efficiency to the minimization of CO2 emissions in the industrial sector. For example the studies of Mahmoud et al. [6] and Tiew et al. [7] investigate methodology based on fuel switching and heat exchanger network (HEN) retrofit for the minimization of atmospheric emissions in flue gases. Pinch analysis has also been adopted to provide conceptual guidance regarding the top-level management of carbon emissions. This involves the use of graphical representations of carbon emissions which are incorporated with energy demand and supply composite curves. Such methods have been implemented by Tan and Foo [8] for the purpose of planning in the energy sector and by Atkins et al. [9] or the purpose of management in the electricity sector. Furthermore, attempts have been made to elaborate these graphic-based methods with the aid of mathematical optimization techniques. For example, an automated targeting method has been suggested by Lee at al. [10], with which the minimum consumption of low-carbon or CO2-neutral energy sources and their optimum configuration are automatically identified. Considering the large number of possible modifications which can be made to the energy systems of a process site it can be a challenge to identify the most appropriate options in terms of the cost effective reduction of CO2 emitted. In the methodology of Gharaie et al. [11] a hierarchical approach is taken which sequentially considers retrofit of HEN, utility system and fuel switching options. Their method generates investment cost vs. reduction of CO2 graphs for each option which can be used to select cost effective solutions combining the three options while satisfying CO2 reduction targets and constraints placed on capital investment. Similarly Al-Mayyahi et al. [12] proposed a graphical method using CO2 emissions and cost composite curves which can also be used to identify cost effective solutions satisfying emission reduction targets. However, in the study of Al-Mayyahi et al. [12] their method uses graphical analysis of only utility system retrofits. While the sequential method of Gharaie et al. [11] considers multiple different retrofit options (HEN, utility and fuel switching), for each retrofit option the emission reductions are plotted on separate graphs and hence comparisons between the different retrofit options and the cumulative reductions obtained from multiple retrofits are not clearly shown. Additionally, while the methods of Gharaie et al. [11] and AlMayyahi et al. [12] both suggest the possibility of generating solutions using different emission limits (Al-Mayyahi et al. [12] suggest the creation of pareto curves), the priori selection of emission targets introduces some bias into the methods which makes “highlevel” comparisons (e.g. considering the basic calculation of CO2
reduction capacity and costs) of different retrofit options more difficult to visualize. For example this would require repeated implementation of the methods with a range of different emission reduction targets to obtain a clear picture showing situations where each retrofit option becomes beneficial. Hence, in this study a holistic “high-level” screening methodology is proposed which allows the comparison of different retrofit options though the construction of graphs showing the site-wide cumulative retrofit costs plotted against the cumulative CO2 avoided (including all possible retrofit options under consideration). These graphs are constructed based on the quantification of the costs and capacity for CO2 reduction of each retrofit option which are ranked in terms of the cost per ton of CO2 avoided. Hence, this graphical representation allows the simple selection and comparison of different potential retrofit options and combinations of different options which can meet any given reduction target within the range considered. In this way the proposed screening method allows a quicker and simpler analysis of different retrofit options compared to existing methods which focus on more detailed investigation of small numbers of different retrofit options or which consider different options in sequence. However, it should be noted that this is a “high-level” screening method and following the selection of appropriate retrofit options a more detailed design should be carried out to find the optimal configuration and operating conditions for the selected retrofits. A case study looking at a refinery plant will be presented to illustrate the developed methodology and to demonstrate the benefits of this approach for the identification of retrofit options giving cost-effective reduction of CO2 emissions.
2. Design issues related to the reduction of CO2 emissions Industrial plants generate energy in the form of steam, electricity or shaft power from the central utility systems in addition to energy generated using local energy-generating equipment (e.g. combustion heat generated in a furnace). Therefore, CO2 emissions from industrial energy infrastructure (as shown in Fig. 1) include emissions from the central utility systems as well as emissions from various local energy generation systems. These energy-generating units are naturally located in various different places and so characteristics of the CO2 emissions (location of the emission source, composition and flow rate of flue gases etc.) should be systematically reflected in the retrofit studies with regard to the reduction of CO2 emissions. Fig. 2 illustrates a number of degrees of freedom in the design and operation of central site utility systems from the viewpoint of retrofit, which can be modified through optimization, leading to higher energy efficiency and lower fuel consumption. The main degrees of freedom include. 1) 2) 3) 4)
the the the the
selection of working loads for each firing machine distribution of working loads between steam turbines allocation of power generation machines degree of steam recovery and cogeneration
Additionally, energy-savings can be found through the retrofit of the various heat exchanger networks (HENs) present on the site to improve heat recovery. Fig. 3 shows a number of possible structural design options for increasing heat recovery in HENs, which lead to fuel savings. These options include: 1) adding a new heat exchanger 2) adding new heat exchanger area to an existing exchanger
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Fig. 1. CO2 emissions in process industries.
3) replacing existing exchangers with those using heat transfer enhancement technology 4) relocation of an exchanger within the network 5) changing the order/sequence of heat exchangers However, there are also options for retrofit through modification of only the operating conditions, for example altering the stream split ratios or through the exploitation of utility paths. In contrast with the operational optimization of site utility systems, it is typically necessary to make structural changes in heat recovery systems to obtaining meaningful energy savings, which implies capital investment is normally required for the retrofit. In addition to energy saving options considering retrofit of the utility or heat exchanger networks it is also possible to reduce emissions through the switching of fuels using in the various heat
generating units. Table 1 shows a few types of fuels commonly used in process industries, including the amounts of CO2 generated by each fuel. These different CO2 emission factors can be exploited through the selection of cleaner fuels generating less CO2, avoiding the combustion of fuels with high CO2 emission factors. This tactic is straightforward and the engineering and construction work required for the implementation of fuel switching is relatively simple and minimal compared to other retrofit options based on structural changes. While the post-combustion capture of CO2 requires the purchase and installation of equipment to extract and remove CO2 it can be simpler to implement in comparison with alternative CO2 capture routes (pre-combustion and oxy-fuel combustion) which require more significant reconfiguration of the site. Amine-based absorption processes (as shown in Fig. 4) are one of the most
Fig. 2. Energy saving options in site utility systems.
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Fig. 3. Structural changes for energy saving in energy recovery systems.
widely-accepted and proven technologies for industrial CO2 capture. In a typical amine-based CO2 removal process flue gas containing carbon dioxide is contacted with lean amine solvent in the absorber which selectively removes carbon dioxide from the gas stream, while rich solvent is passed to the stripping column where it is re-generated and recycled (Fig. 4). Considerable energy is consumed in these processes including the heat required for regeneration of the amine solvent, pumping of the recycled amine solvent and compression of the recovered CO2 to high pressure levels required for transportation. A holistic approach should consider all of these options combining energy saving methods with CO2 capture where necessary to reduce CO2 emissions considering the various constraints and limitations (e.g. capital investment limits). 3. Design methodology for site-wide CO2 emissions reduction Due to design complexities and the large number of possible options for the reduction of CO2 emissions through retrofit, it is logical to develop a systematic screening strategy which gives clear guidelines about the most beneficial options for site-wide decarbonization. In this study, TAC (total annualized cost) required for decarbonization per ton of CO2 avoided is selected as the economic indicator to use for comparison and ranking of different design options among those selected for consideration. The detailed screening procedure is given in Fig. 5, which shows the step-bystep actions required as part of the analysis. Firstly, all the possible options site-wide CO2 emissions reduction should be identified. These options are then evaluated to determine the costs required and the amount of CO2 reduced by each design option. The screening procedure in this study does not require initially the detailed optimization of each retrofit option
Table 1 CO2 emissions [13], heating values and costs [14] of common fuels. Fuel type
kg CO2 per kWh
Heating value (kWh/kg)
Cost ($/kg)
Coal (industrial) Fuel oil LNG
0.30073 0.28913 0.18706
7.777 11.111 14.444
0.065 0.12 0.22
(1 kWh ¼ 3600 kJ).
and will instead rely on either typical equipment configurations or the evaluation and comparison of a limited number of different configurations. In this way appropriate designs are identified allowing the simple calculation of costs and emission reductions for each retrofit method and for each emission source. This screening approach does not consider the interactions between different retrofits options and so the identified retrofit options by this procedure should be optimized together using more rigorous methods to confirm the exact CO2 reduction and costs involved. Once the total annualized cost (TAC) is obtained for each possible retrofit together with the decarbonization impact this data can then be plotted in a graph showing the costs involved and the cumulative CO2 avoided (as shown in Fig. 6). After ranking the different design options in terms of cost and decarbonization engineering judgment should be used by engineers to select the most promising options for further consideration and to remove any undesirable options which may have associated engineering difficulties or practical obstacles (Fig. 7). Based on the selected decarbonization options a profile of cumulative CO2 abatement cost can be constructed as shown in Fig. 8. This contains the costs and CO2 emission reductions possible through application of the selected retrofits in order of cost
CO2 Flue Gas stream Without CO2
Recycle Amine Solvent
Absorber
Flue Gas Stream with CO2
Spent Amine Solvent Fig. 4. Amine-based CO2 removal process.
Stripper
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Fig. 5. Strategy for site-wide CO2 emissions reduction in process industries.
Fig. 6. Ranking design options for CO2 emissions reduction.
Fig. 7. Selection of design options for CO2 emissions reduction.
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Fig. 8. Construction of the cumulative CO2 abatement cost profile.
effectiveness (TAC/tCO2 avoided). Hence, if an emission reduction target is selected this graph can be used to identify a sub-set of the most cost-effective retrofits which can be implemented to meet that target. This can be extended through the inclusion of cumulative capital investment costs for each of the retrofit options (Fig. 9). Where in this graph the left axis and the lower line (shown as blue in the web version) refer to the TAC/tCO2 avoided and the right axis together with the upper line (shown as red in the web version) refer to the accumulated capital investment costs for the combination of retrofits. This information contained in the investment cost profile can be used as part of the decision-making process together with the CO2 emissions reduction targets and the level of capital investment allowed (as shown in Fig. 10).
characteristics of both the retrofit options and the streams containing emitted CO2. For amine-based CO2 capture processes the cost per ton of CO2 avoided is a function of the CO2 content and flow rate of the flue
4. Economic evaluation of CO2 emissions reduction It is important to accurately evaluate the economic impacts associated with retrofit options for the reduction of CO2 emissions in order to screen various different design options and to select and implement the most appropriate retrofit. For a given case the capital investment and operating costs will be dependent on the
Fig. 9. Construction of the cumulative capital investment cost of CO2 emissions reduction profile.
Fig. 10. Decision-making for site-wide CO2 emissions reduction.
K.-J. Min et al. / Applied Thermal Engineering 90 (2015) 335e344
gas. In particular the capital costs of the absorber and stripper columns are strongly influenced by the flow rate of gases being treated. Also, the energy costs are heavily influenced by the level of CO2 recovery. This has been addressed by van Straelen et al. [15] who investigated the cost of CO2 avoided in relation to the amount of CO2 captured and the CO2 composition. For evaluation of costs related to energy-saving retrofit projects two cases are considered here: energy saving with only operational changes and energy saving with both structural and operational changes. When energy saving is achieved without capital investment (i.e. operational changes only) the reduction in operating costs through fuel savings can be calculated easily from the unit costs of fuels shown in Table 1. For retrofit requiring capital investment (i.e. structural changes) this capital investment required is weighed against economic gains obtained through fuel savings. Care must be taken as the amount of energy savings may not always outweigh the investment costs for a given retrofit. There are many design methods for the retrofit of HENs and the final results will strongly depend on the methodology selected and on the users' preferences. One of the most widely-used methodologies is “network pinch” [4,5] in which a series of retrofit options are generated with the aid of optimization. Possible options generated from HEN retrofit studies can be listed and treated individually as discrete options while regression can be carried out using a set of retrofit results to generate a cost function curve (as illustrated in Fig. 11). This cost function may not accurately reflect the full range of options since discrete points have been selected. However, this information can be useful for top-down analysis. For fuel switching the modified operating costs resulted from using cleaner fuels can be calculated based on fuel unit costs and heating values (as given in Table 1). The capital investment required for fuel switching which has not been fully addressed in other studies can be estimated using a factor multiplied by the overall heat duties of the furnaces or boilers. This factor for assessing the capital costs of fuel switching can be obtained from the Environmental Protection Agency (EPA) [16].
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Considering the capital and operating costs of each retrofit option, the total annualized costs can be calculated using equations (1) and (2) by specifying the project lifetime (n years) and interest rate (i x 100%) and calculating the annualization factor (AF).
TAC ¼ AF Ccapital þCoperating AF ¼
ið1 þ iÞn ð1 þ iÞn 1
(1)
(2)
5. Case study The proposed methodology has been applied to a case study which is adopted from data provided by Gharaie [17]. This case refers to a refinery with a central utility system including four boilers generate steam and consuming 217 kt/yr of coal. Four different options are considered for the retrofit of the heat recovery systems (where heaters using fuel oil are employed to provide heat at a local level). Options other than these four identified modifications are not investigated here as they were found to have very low potential for reducing CO2 emissions at the site. Table 2 gives information showing details of the CO2 generated at the site, the amount of fuel consumed and the duties of local furnaces as well as boilers in the central utility system. The compositions of CO2 in the flue gases of the boilers and local heaters are assumed to be 8% for boilers in site utility systems, 4% for local heaters in Processes 1 and 4, 8% for local heaters in Processes 2 and 5, and 12% for local heaters in Processes 3 and 6. The following four retrofit options are considered for reducing CO2 emissions at the site: 5% energy saving in terms of steam generated in boilers is achieved through operational optimization of the site utility system. This action results in fuel savings in the boilers of utility
Fig. 11. Illustration for determining the costs of energy saving projects.
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Table 2 Case study: sources of CO2 emissions at a refinery. Processes
Equipment
Duty [MW]
Before fuel switching(Boilers using coal and local heaters using fuel oil) Fuel required [kt/year]
Utility systems
Boiler 1 Boiler 2 Boiler 3 Boiler 4 Subtotal
Process 1~6 ss 6
Local heater Local heater Local heater Local heater Local heater Local heater Subtotal
1 2 3 4 5 6
Fuel cost [MM$/year]
CO2 generated [kt/year]
After fuel switching (using only LNG) Fuel required [kt/year]
Fuel cost [MM$/year]
CO2 generated [kt/year]
58.94 52.08 37.01 24.67 172.70
74.06 65.44 46.50 31.00 217
4.81 4.25 3.02 2.02 14.11
173.22 153.07 108.76 72.51 507.56
39.88 35.24 25.04 16.69 116.85
8.77 7.75 5.51 3.67 25.71
107.75 95.22 67.65 45.10 315.72
597.50 182.58 86.30 71.91 12.93 6.10 957.32
525.53 160.59 75.90 63.25 11.37 5.37 842.01
63.06 19.27 9.11 7.59 1.36 0.64 101.04
1688.26 515.89 243.84 203.18 36.53 17.24 2704.95
404.25 123.53 58.39 48.65 8.75 4.13 647.70
88.94 27.18 12.85 10.70 1.92 0.91 142.49
1092.29 333.77 157.77 131.46 23.64 11.15 1750.08
Other processes Total site
1000 4212.51
system and in this case study the fuel consumption is reduced only in Boiler 1 (other options are possible). Energy savings through retrofit of the heat recovery systems in Processes 1, 2, 3 and 4 are assumed to directly reduce the associated local furnace duties by 40 MW (6.7% saving), 15 MW (8.2% saving), 5 MW (5.8% saving) and 12 MW (16.7% saving), respectively in addition to an indirect reduction of boiler duty in the central utility system (reduced by 14.4 MW (20% savings) in Boiler 2). Fuel switching is implemented in all the boilers and local heaters. The fuel used in the boilers of the utility system is switched from coal to LNG, while the fuel oil used in local heaters is also switched to LNG (the effects of fuel switching on emissions and costs are also shown in Table 2). 90% of emitted CO2 is removed using end-of-pipe CO2 capture. For this option it is assumed that each local heater and boiler has a dedicated CO2 capture unit. This means that flue gases are not gathered and piped to a central facility for CO2 removal. The following economic and costing basis is assumed for the case study: The capital investment required for fuel switching is calculated with equation (3) [15]. Original costs based on the year 2002 (chemical engineering index 395.6) are updated with values for January of 2012 (chemical engineering index 593.6):
CFS ¼ 0:01896Q FUEL
(3)
where CFS is the capital investment required for fuel switching in million US$, and QFUEL is the duty of the furnace in MW. The capital investment for energy saving projects is assumed to follow the correlation (equation (4)):
CES ¼ 0:003Q ES 2 þ 0:0249Q ES þ 1:5498
(4)
where CES is the capital investment required for retrofit of heat recovery systems in million US$, and Q is the size of the duty reduction following the retrofit in MW. This expression is developed based estimates of cost and energy reductions in a similar way to the expression used by Gadalla et al. [18] to relate heat exchanger area to energy reduction.
1000 3065.80
The equations for the cost of post-combustion CO2 capture used in this case study are established through regression of the data reported by van Straelen et al. [15] giving the correlations in equations (5)e(7). These costs valid for the year 2007 (chemical engineering index 525.4) are updated with values for January of 2012 (chemical engineering index 593.6).
CCC ¼ 414:12XCO2 0:169
ðfor 4% CO2 in flue gasÞ
(5)
CCC ¼ 335:31XCO2 0:164
ðfor 8% CO2 in flue gasÞ
(6)
CCC ¼ 298:12XCO2 0:155
ðfor 12% CO2 in flue gasÞ
(7)
where CCC is the capital investment required for post-combustion CO2 capture in Euro/CO2 captured and XCO2 is the amount of CO2 captured in ktCO2/yr. For calculation of the annualized capital costs a 12% rate of interest and 3 year project life time are taken. 0.8 Euros are assumed to be equivalent to 1 USD. Fuel costs and CO2 emission factors used are those given in Tables 1 and 2 With this costing basis and the retrofit options described above the profile of CO2 capital investment costs is constructed and plotted against cumulative CO2 avoided (in Fig. 12). The profile of cumulative capital costs required for decarbonization of the site is also constructed (Fig. 13). When the same design options for CO2 reduction are applied to different processes or units those design options are applied first to units or processes having larger energy duties (before considering those with lower energy duties). For example when retrofitting the energy recovery systems, processes 1 to 4 are considered in sequence (with process 1 given the highest priority). Fig. 12 also indicates a number of different targets for CO2 avoided (20%, 40% and 60%) in the retrofit study which can help users with retrofit decision-making. It is worth noting here that all the possible retrofit options are considered when constructing these profiles, although some options may be eliminated at an early stage. These graphs generated by the screening procedure described here can be used for the top-level assessment of various design options reducing CO2 emissions. Hence, this methodology focuses
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Fig. 12. Case study: Decision-making for site-wide CO2 emissions reduction (I).
on the selection of appropriate retrofit technologies rather than providing design schemes or methods for the implementation at the site. Detailed process design for fuel switching, retrofit of energy recovery systems, or operational optimization of site utility systems would be required before any final decisions are made for this case study. 6. Conclusions and future work A new screening procedure has been developed with the aim to identify appropriate decarbonization retrofit options for industrial sites. This methodology systematically evaluates and ranks different options based on their costs and potential capacity for the reduction of CO2 emitted at a site. Utilizing this information the accumulated CO2 avoided versus the accumulated investment costs required can be calculated and shown graphically including multiple different retrofit options applied to multiple different sources
of CO2 in a site. Analysis of these graphs can be used to provide guidance for the “high-level” decision making process related to the selection of retrofit options. A case study has been presented to demonstrate the applicability of the proposed design methodology and to explain how the resulting analysis can be used to aid decision-making in practice. This provides conceptual understanding and physical insights regarding the implementation of carbon capture technology at process industries. Advances have been made in the development of design methodologies for the site-wide reduction of CO2 emissions. However, there are a few areas which need to be investigated in more detail as part of future work. As this study focuses on the screening and comparison of different options this procedure could be extended to include optimization of the selected combinations of retrofit option to meet emission targets and satisfy constraints on capital investment. In particular the rigorous design and optimization of the internal parameters in each retrofit should be carried
Fig. 13. Case study: Decision-making for site-wide CO2 emissions reduction (II).
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out including any interactions between different retrofits to confirm the feasibility of suggested combinations of retrofits. Acknowledgements This work was supported by the research fund of Hanyang University (HY-2013). References [1] B. Linnhoff, D.W. Townsend, D. Boland, G.F. Hewitt, B.E.A. Thomas, A.R. Guy, R.H. Marsland, A User Guide on Process Integration for the Efficient Use of Energy, IChemE, Rugby, 1982. [2] I.C. Kemp, Pinch Analysis and Process Integration: a User Guide on Process Integration of the Efficient Use of Energy, second ed., Elsevier, Oxford, 2007. [3] J. Klemes, F. Friedler, I. Bulatov, P. Varbanov, Sustainability in the Process Industry: Integration and Optimization, McGraw Hill, New York, 2010. [4] R. Smith, Chemical Process Design and Integration, Wiley, Chichester, 2005. [5] R. Smith, M. Jobson, L. Chen, Recent development in the retrofit of heat exchanger networks, Appl. Therm. Eng. 30 (2010) 2281e2289. [6] A. Mahmoud, M. Shuhaimi, M. Abdel Samed, A combined process integration and fuel switching strategy for emissions reduction in chemical process plants, Energy 34 (2009) 190e195. [7] B.J. Tiew, M. Shuhaimi, H. Hashim, Carbon emission reduction targeting through process integration and fuel switching with mathematical modeling, Appl. Energy 92 (2012) 686e693. [8] R.R. Tan, D.C.Y. Foo, Pinch analysis approach to carbon-constrained energy sector planning, Energy 33 (2007) 1422e1429.
[9] M.J. Atkins, A.S. Morrison, M.R.W. Walmsley, Carbon Emissions Pinch Analysis (CEPA) for emissions reduction in the New Zealand electricity sector, Appl. Energy 87 (2010) 982e987. [10] S.C. Lee, D.K.S. Ng, D.C.Y. Foo, R.R. Tan, Extended pinch targeting techniques for carbon-constrained energy sector planning, Appl. Energy 86 (2009) 60e67. [11] M. Gharaie, M.H. Panjeshahi, J. Kim, M. Jobson, R. Smith, Retrofit strategy for the site-wide mitigation of CO2 emissions in the process industries, Chem. Eng. Res. Des. 94 (2015) 213e241. [12] M.A. Al-Mayyahi, A.F.A. Hoadley, G.P. Rangaiah, A novel graphical approach to target CO2 emissions for energy resource planning and utility system optimization, Appl. Energy 104 (2013) 783e790. [13] Defra/DECC, 2011 Guidelines to Defra/DECC's GHG Conversion Factors for Company Reporting, Defra/DECC, London, 2011. [14] P. Varbanov, S. Perry, Y. Makwana, X.X. Zhu, R. Smith, Top-level analysis of site utility systems, Chem. Eng. Res. Des. 82 (2004) 784e795. [15] J. van Straelen, F. Geuzebroek, N. Goodchild, G. Protopapas, L. Mahony, CO2 capture for refineries, a practical approach, Int. J. Greenh. Gas Control 4 (2010) 316e320. [16] EPA (Environmental Protection Agency), Development of fuel switching costs and emission reductions for industrial/commercial/institutional boilers and process heaters: national emission standards for hazardous air pollutants (TS0000324A), EPA (2002). http://yosemite1.epa.gov/ee/epa/ria.nsf/vwTD/ E3DBACB6F5E0A60985256CE50069542A. [17] M. Gharaie, Design and optimization of energy systems for effective carbon control, in: Process Integration Research Consortium 2011 Research Meeting, The University of Manchester, 2011. [18] M. Gadalla, M. Jobson, R. Smith, Optimization of existing heat-integrated refinery distillation systems, Chem. Eng. Res. Des. 81 (2003) 147e152.
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Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng
Research paper
Screening of site-wide retrofit options for the minimization of CO2 emissions in process industries Kwang-Joon Min, Michael Binns, Se-Young Oh, Hyun-Young Cha, Jin-Kuk Kim*, Yeong-Koo Yeo Department of Chemical Engineering, Hanyang University, 222 Wangshimni-ro, Seongdong-gu, Seoul, 133-791, Republic of Korea
h i g h l i g h t s Systematic screening of retrofit options for the minimization of CO2 emissions. A holistic view considering multiple sources of CO2 and multiple retrofit options. Graphical methods to suggest the most cost-effective combinations of retrofits.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 March 2015 Accepted 4 July 2015 Available online 13 July 2015
This paper addresses the systematic screening of possible retrofit options for the minimization of CO2 emissions from process industries. In retrofit scenarios there are various options for the reduction of CO2 emitted which can be considered with different costs and capacities for CO2 reduction/removal. This study considers a holistic view accounting for multiple sources of CO2 emitted from a site and multiple potential retrofit options which can be implemented individually or in combination to meet CO2 reduction targets. For a given site the different possible retrofit options are ranked in terms of costeffectiveness and the most appropriate options are highlighted using graphical methods to suggest the most cost-effective combinations of retrofits. A case study is used to demonstrate the applicability of the proposed design methodology. This case study illustrates how fuel switching and energy-saving projects can be practical and beneficial measures for the implementation of decarbonization in process industries. © 2015 Elsevier Ltd. All rights reserved.
Keywords: CO2 capture Retrofit Energy savings Fuel switching Process design
1. Introduction Industrial plants such as refineries and petrochemical plants etc. emit flue gases from various sources with different CO2 compositions and flow rates. These sources of CO2 emissions will typically be found at different locations in the plant unlike conventional power plants which will generally have just a single source of CO2 emissions (flue gas from the combustion units). The reduction of CO2 emissions can be achieved through various different methods. These methods can be divided into three different categories:
* Corresponding author. Tel.: þ82 2 2220 2331. E-mail address: [email protected] (J.-K. Kim). http://dx.doi.org/10.1016/j.applthermaleng.2015.07.008 1359-4311/© 2015 Elsevier Ltd. All rights reserved.
1) Process modification 2) Energy systems modification 3) CO2 capture Modifications applied to the processes or to the energy systems are generally aimed at reducing the energy consumption (and also costs) which lead to the indirect reduction of CO2 emissions for example due to reduced fuel consumption. Alternatively CO2 capture involves the direct extraction and removal of the generated CO2 (e.g. from emitted flue gases). The implemented modifications are limited by a number of constraints when considering the retrofit of an existing site. Possibly the most important constraints are the upper limits placed on capital investment required to purchase new equipment but also there may be practical engineering constraints (e.g. limited space for equipment and for gathering/ducting flue gases due to the plant layout).
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Hence, CO2 capture and process/energy system modifications requiring additional equipment may be considered unfavorable due to the investment costs required. The most desirable options are energy-saving retrofit projects without any process modifications or additional capital investment required on the site. One such example of this type of ideal retrofit project is the energy-saving achieved through operational optimization of site utility systems. However, in terms of the total site-wide CO2 reduction the impact of this single retrofit option may not be significant and so a retrofit including multiple different modifications should be considered to achieve a more substantial reduction of CO2 emissions. When considering the modification of energy systems heat integration techniques can be applied to assess theoretical potential energy savings in the plant with the aid of energy targeting tools [1e3], network pinch methods [4] or superstructure-based optimization methods [5] which can identify options giving the greatest reduction of energy consumption. In addition studies have also been carried out linking the improvement of energy efficiency to the minimization of CO2 emissions in the industrial sector. For example the studies of Mahmoud et al. [6] and Tiew et al. [7] investigate methodology based on fuel switching and heat exchanger network (HEN) retrofit for the minimization of atmospheric emissions in flue gases. Pinch analysis has also been adopted to provide conceptual guidance regarding the top-level management of carbon emissions. This involves the use of graphical representations of carbon emissions which are incorporated with energy demand and supply composite curves. Such methods have been implemented by Tan and Foo [8] for the purpose of planning in the energy sector and by Atkins et al. [9] or the purpose of management in the electricity sector. Furthermore, attempts have been made to elaborate these graphic-based methods with the aid of mathematical optimization techniques. For example, an automated targeting method has been suggested by Lee at al. [10], with which the minimum consumption of low-carbon or CO2-neutral energy sources and their optimum configuration are automatically identified. Considering the large number of possible modifications which can be made to the energy systems of a process site it can be a challenge to identify the most appropriate options in terms of the cost effective reduction of CO2 emitted. In the methodology of Gharaie et al. [11] a hierarchical approach is taken which sequentially considers retrofit of HEN, utility system and fuel switching options. Their method generates investment cost vs. reduction of CO2 graphs for each option which can be used to select cost effective solutions combining the three options while satisfying CO2 reduction targets and constraints placed on capital investment. Similarly Al-Mayyahi et al. [12] proposed a graphical method using CO2 emissions and cost composite curves which can also be used to identify cost effective solutions satisfying emission reduction targets. However, in the study of Al-Mayyahi et al. [12] their method uses graphical analysis of only utility system retrofits. While the sequential method of Gharaie et al. [11] considers multiple different retrofit options (HEN, utility and fuel switching), for each retrofit option the emission reductions are plotted on separate graphs and hence comparisons between the different retrofit options and the cumulative reductions obtained from multiple retrofits are not clearly shown. Additionally, while the methods of Gharaie et al. [11] and AlMayyahi et al. [12] both suggest the possibility of generating solutions using different emission limits (Al-Mayyahi et al. [12] suggest the creation of pareto curves), the priori selection of emission targets introduces some bias into the methods which makes “highlevel” comparisons (e.g. considering the basic calculation of CO2
reduction capacity and costs) of different retrofit options more difficult to visualize. For example this would require repeated implementation of the methods with a range of different emission reduction targets to obtain a clear picture showing situations where each retrofit option becomes beneficial. Hence, in this study a holistic “high-level” screening methodology is proposed which allows the comparison of different retrofit options though the construction of graphs showing the site-wide cumulative retrofit costs plotted against the cumulative CO2 avoided (including all possible retrofit options under consideration). These graphs are constructed based on the quantification of the costs and capacity for CO2 reduction of each retrofit option which are ranked in terms of the cost per ton of CO2 avoided. Hence, this graphical representation allows the simple selection and comparison of different potential retrofit options and combinations of different options which can meet any given reduction target within the range considered. In this way the proposed screening method allows a quicker and simpler analysis of different retrofit options compared to existing methods which focus on more detailed investigation of small numbers of different retrofit options or which consider different options in sequence. However, it should be noted that this is a “high-level” screening method and following the selection of appropriate retrofit options a more detailed design should be carried out to find the optimal configuration and operating conditions for the selected retrofits. A case study looking at a refinery plant will be presented to illustrate the developed methodology and to demonstrate the benefits of this approach for the identification of retrofit options giving cost-effective reduction of CO2 emissions.
2. Design issues related to the reduction of CO2 emissions Industrial plants generate energy in the form of steam, electricity or shaft power from the central utility systems in addition to energy generated using local energy-generating equipment (e.g. combustion heat generated in a furnace). Therefore, CO2 emissions from industrial energy infrastructure (as shown in Fig. 1) include emissions from the central utility systems as well as emissions from various local energy generation systems. These energy-generating units are naturally located in various different places and so characteristics of the CO2 emissions (location of the emission source, composition and flow rate of flue gases etc.) should be systematically reflected in the retrofit studies with regard to the reduction of CO2 emissions. Fig. 2 illustrates a number of degrees of freedom in the design and operation of central site utility systems from the viewpoint of retrofit, which can be modified through optimization, leading to higher energy efficiency and lower fuel consumption. The main degrees of freedom include. 1) 2) 3) 4)
the the the the
selection of working loads for each firing machine distribution of working loads between steam turbines allocation of power generation machines degree of steam recovery and cogeneration
Additionally, energy-savings can be found through the retrofit of the various heat exchanger networks (HENs) present on the site to improve heat recovery. Fig. 3 shows a number of possible structural design options for increasing heat recovery in HENs, which lead to fuel savings. These options include: 1) adding a new heat exchanger 2) adding new heat exchanger area to an existing exchanger
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Fig. 1. CO2 emissions in process industries.
3) replacing existing exchangers with those using heat transfer enhancement technology 4) relocation of an exchanger within the network 5) changing the order/sequence of heat exchangers However, there are also options for retrofit through modification of only the operating conditions, for example altering the stream split ratios or through the exploitation of utility paths. In contrast with the operational optimization of site utility systems, it is typically necessary to make structural changes in heat recovery systems to obtaining meaningful energy savings, which implies capital investment is normally required for the retrofit. In addition to energy saving options considering retrofit of the utility or heat exchanger networks it is also possible to reduce emissions through the switching of fuels using in the various heat
generating units. Table 1 shows a few types of fuels commonly used in process industries, including the amounts of CO2 generated by each fuel. These different CO2 emission factors can be exploited through the selection of cleaner fuels generating less CO2, avoiding the combustion of fuels with high CO2 emission factors. This tactic is straightforward and the engineering and construction work required for the implementation of fuel switching is relatively simple and minimal compared to other retrofit options based on structural changes. While the post-combustion capture of CO2 requires the purchase and installation of equipment to extract and remove CO2 it can be simpler to implement in comparison with alternative CO2 capture routes (pre-combustion and oxy-fuel combustion) which require more significant reconfiguration of the site. Amine-based absorption processes (as shown in Fig. 4) are one of the most
Fig. 2. Energy saving options in site utility systems.
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Fig. 3. Structural changes for energy saving in energy recovery systems.
widely-accepted and proven technologies for industrial CO2 capture. In a typical amine-based CO2 removal process flue gas containing carbon dioxide is contacted with lean amine solvent in the absorber which selectively removes carbon dioxide from the gas stream, while rich solvent is passed to the stripping column where it is re-generated and recycled (Fig. 4). Considerable energy is consumed in these processes including the heat required for regeneration of the amine solvent, pumping of the recycled amine solvent and compression of the recovered CO2 to high pressure levels required for transportation. A holistic approach should consider all of these options combining energy saving methods with CO2 capture where necessary to reduce CO2 emissions considering the various constraints and limitations (e.g. capital investment limits). 3. Design methodology for site-wide CO2 emissions reduction Due to design complexities and the large number of possible options for the reduction of CO2 emissions through retrofit, it is logical to develop a systematic screening strategy which gives clear guidelines about the most beneficial options for site-wide decarbonization. In this study, TAC (total annualized cost) required for decarbonization per ton of CO2 avoided is selected as the economic indicator to use for comparison and ranking of different design options among those selected for consideration. The detailed screening procedure is given in Fig. 5, which shows the step-bystep actions required as part of the analysis. Firstly, all the possible options site-wide CO2 emissions reduction should be identified. These options are then evaluated to determine the costs required and the amount of CO2 reduced by each design option. The screening procedure in this study does not require initially the detailed optimization of each retrofit option
Table 1 CO2 emissions [13], heating values and costs [14] of common fuels. Fuel type
kg CO2 per kWh
Heating value (kWh/kg)
Cost ($/kg)
Coal (industrial) Fuel oil LNG
0.30073 0.28913 0.18706
7.777 11.111 14.444
0.065 0.12 0.22
(1 kWh ¼ 3600 kJ).
and will instead rely on either typical equipment configurations or the evaluation and comparison of a limited number of different configurations. In this way appropriate designs are identified allowing the simple calculation of costs and emission reductions for each retrofit method and for each emission source. This screening approach does not consider the interactions between different retrofits options and so the identified retrofit options by this procedure should be optimized together using more rigorous methods to confirm the exact CO2 reduction and costs involved. Once the total annualized cost (TAC) is obtained for each possible retrofit together with the decarbonization impact this data can then be plotted in a graph showing the costs involved and the cumulative CO2 avoided (as shown in Fig. 6). After ranking the different design options in terms of cost and decarbonization engineering judgment should be used by engineers to select the most promising options for further consideration and to remove any undesirable options which may have associated engineering difficulties or practical obstacles (Fig. 7). Based on the selected decarbonization options a profile of cumulative CO2 abatement cost can be constructed as shown in Fig. 8. This contains the costs and CO2 emission reductions possible through application of the selected retrofits in order of cost
CO2 Flue Gas stream Without CO2
Recycle Amine Solvent
Absorber
Flue Gas Stream with CO2
Spent Amine Solvent Fig. 4. Amine-based CO2 removal process.
Stripper
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Fig. 5. Strategy for site-wide CO2 emissions reduction in process industries.
Fig. 6. Ranking design options for CO2 emissions reduction.
Fig. 7. Selection of design options for CO2 emissions reduction.
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Fig. 8. Construction of the cumulative CO2 abatement cost profile.
effectiveness (TAC/tCO2 avoided). Hence, if an emission reduction target is selected this graph can be used to identify a sub-set of the most cost-effective retrofits which can be implemented to meet that target. This can be extended through the inclusion of cumulative capital investment costs for each of the retrofit options (Fig. 9). Where in this graph the left axis and the lower line (shown as blue in the web version) refer to the TAC/tCO2 avoided and the right axis together with the upper line (shown as red in the web version) refer to the accumulated capital investment costs for the combination of retrofits. This information contained in the investment cost profile can be used as part of the decision-making process together with the CO2 emissions reduction targets and the level of capital investment allowed (as shown in Fig. 10).
characteristics of both the retrofit options and the streams containing emitted CO2. For amine-based CO2 capture processes the cost per ton of CO2 avoided is a function of the CO2 content and flow rate of the flue
4. Economic evaluation of CO2 emissions reduction It is important to accurately evaluate the economic impacts associated with retrofit options for the reduction of CO2 emissions in order to screen various different design options and to select and implement the most appropriate retrofit. For a given case the capital investment and operating costs will be dependent on the
Fig. 9. Construction of the cumulative capital investment cost of CO2 emissions reduction profile.
Fig. 10. Decision-making for site-wide CO2 emissions reduction.
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gas. In particular the capital costs of the absorber and stripper columns are strongly influenced by the flow rate of gases being treated. Also, the energy costs are heavily influenced by the level of CO2 recovery. This has been addressed by van Straelen et al. [15] who investigated the cost of CO2 avoided in relation to the amount of CO2 captured and the CO2 composition. For evaluation of costs related to energy-saving retrofit projects two cases are considered here: energy saving with only operational changes and energy saving with both structural and operational changes. When energy saving is achieved without capital investment (i.e. operational changes only) the reduction in operating costs through fuel savings can be calculated easily from the unit costs of fuels shown in Table 1. For retrofit requiring capital investment (i.e. structural changes) this capital investment required is weighed against economic gains obtained through fuel savings. Care must be taken as the amount of energy savings may not always outweigh the investment costs for a given retrofit. There are many design methods for the retrofit of HENs and the final results will strongly depend on the methodology selected and on the users' preferences. One of the most widely-used methodologies is “network pinch” [4,5] in which a series of retrofit options are generated with the aid of optimization. Possible options generated from HEN retrofit studies can be listed and treated individually as discrete options while regression can be carried out using a set of retrofit results to generate a cost function curve (as illustrated in Fig. 11). This cost function may not accurately reflect the full range of options since discrete points have been selected. However, this information can be useful for top-down analysis. For fuel switching the modified operating costs resulted from using cleaner fuels can be calculated based on fuel unit costs and heating values (as given in Table 1). The capital investment required for fuel switching which has not been fully addressed in other studies can be estimated using a factor multiplied by the overall heat duties of the furnaces or boilers. This factor for assessing the capital costs of fuel switching can be obtained from the Environmental Protection Agency (EPA) [16].
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Considering the capital and operating costs of each retrofit option, the total annualized costs can be calculated using equations (1) and (2) by specifying the project lifetime (n years) and interest rate (i x 100%) and calculating the annualization factor (AF).
TAC ¼ AF Ccapital þCoperating AF ¼
ið1 þ iÞn ð1 þ iÞn 1
(1)
(2)
5. Case study The proposed methodology has been applied to a case study which is adopted from data provided by Gharaie [17]. This case refers to a refinery with a central utility system including four boilers generate steam and consuming 217 kt/yr of coal. Four different options are considered for the retrofit of the heat recovery systems (where heaters using fuel oil are employed to provide heat at a local level). Options other than these four identified modifications are not investigated here as they were found to have very low potential for reducing CO2 emissions at the site. Table 2 gives information showing details of the CO2 generated at the site, the amount of fuel consumed and the duties of local furnaces as well as boilers in the central utility system. The compositions of CO2 in the flue gases of the boilers and local heaters are assumed to be 8% for boilers in site utility systems, 4% for local heaters in Processes 1 and 4, 8% for local heaters in Processes 2 and 5, and 12% for local heaters in Processes 3 and 6. The following four retrofit options are considered for reducing CO2 emissions at the site: 5% energy saving in terms of steam generated in boilers is achieved through operational optimization of the site utility system. This action results in fuel savings in the boilers of utility
Fig. 11. Illustration for determining the costs of energy saving projects.
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Table 2 Case study: sources of CO2 emissions at a refinery. Processes
Equipment
Duty [MW]
Before fuel switching(Boilers using coal and local heaters using fuel oil) Fuel required [kt/year]
Utility systems
Boiler 1 Boiler 2 Boiler 3 Boiler 4 Subtotal
Process 1~6 ss 6
Local heater Local heater Local heater Local heater Local heater Local heater Subtotal
1 2 3 4 5 6
Fuel cost [MM$/year]
CO2 generated [kt/year]
After fuel switching (using only LNG) Fuel required [kt/year]
Fuel cost [MM$/year]
CO2 generated [kt/year]
58.94 52.08 37.01 24.67 172.70
74.06 65.44 46.50 31.00 217
4.81 4.25 3.02 2.02 14.11
173.22 153.07 108.76 72.51 507.56
39.88 35.24 25.04 16.69 116.85
8.77 7.75 5.51 3.67 25.71
107.75 95.22 67.65 45.10 315.72
597.50 182.58 86.30 71.91 12.93 6.10 957.32
525.53 160.59 75.90 63.25 11.37 5.37 842.01
63.06 19.27 9.11 7.59 1.36 0.64 101.04
1688.26 515.89 243.84 203.18 36.53 17.24 2704.95
404.25 123.53 58.39 48.65 8.75 4.13 647.70
88.94 27.18 12.85 10.70 1.92 0.91 142.49
1092.29 333.77 157.77 131.46 23.64 11.15 1750.08
Other processes Total site
1000 4212.51
system and in this case study the fuel consumption is reduced only in Boiler 1 (other options are possible). Energy savings through retrofit of the heat recovery systems in Processes 1, 2, 3 and 4 are assumed to directly reduce the associated local furnace duties by 40 MW (6.7% saving), 15 MW (8.2% saving), 5 MW (5.8% saving) and 12 MW (16.7% saving), respectively in addition to an indirect reduction of boiler duty in the central utility system (reduced by 14.4 MW (20% savings) in Boiler 2). Fuel switching is implemented in all the boilers and local heaters. The fuel used in the boilers of the utility system is switched from coal to LNG, while the fuel oil used in local heaters is also switched to LNG (the effects of fuel switching on emissions and costs are also shown in Table 2). 90% of emitted CO2 is removed using end-of-pipe CO2 capture. For this option it is assumed that each local heater and boiler has a dedicated CO2 capture unit. This means that flue gases are not gathered and piped to a central facility for CO2 removal. The following economic and costing basis is assumed for the case study: The capital investment required for fuel switching is calculated with equation (3) [15]. Original costs based on the year 2002 (chemical engineering index 395.6) are updated with values for January of 2012 (chemical engineering index 593.6):
CFS ¼ 0:01896Q FUEL
(3)
where CFS is the capital investment required for fuel switching in million US$, and QFUEL is the duty of the furnace in MW. The capital investment for energy saving projects is assumed to follow the correlation (equation (4)):
CES ¼ 0:003Q ES 2 þ 0:0249Q ES þ 1:5498
(4)
where CES is the capital investment required for retrofit of heat recovery systems in million US$, and Q is the size of the duty reduction following the retrofit in MW. This expression is developed based estimates of cost and energy reductions in a similar way to the expression used by Gadalla et al. [18] to relate heat exchanger area to energy reduction.
1000 3065.80
The equations for the cost of post-combustion CO2 capture used in this case study are established through regression of the data reported by van Straelen et al. [15] giving the correlations in equations (5)e(7). These costs valid for the year 2007 (chemical engineering index 525.4) are updated with values for January of 2012 (chemical engineering index 593.6).
CCC ¼ 414:12XCO2 0:169
ðfor 4% CO2 in flue gasÞ
(5)
CCC ¼ 335:31XCO2 0:164
ðfor 8% CO2 in flue gasÞ
(6)
CCC ¼ 298:12XCO2 0:155
ðfor 12% CO2 in flue gasÞ
(7)
where CCC is the capital investment required for post-combustion CO2 capture in Euro/CO2 captured and XCO2 is the amount of CO2 captured in ktCO2/yr. For calculation of the annualized capital costs a 12% rate of interest and 3 year project life time are taken. 0.8 Euros are assumed to be equivalent to 1 USD. Fuel costs and CO2 emission factors used are those given in Tables 1 and 2 With this costing basis and the retrofit options described above the profile of CO2 capital investment costs is constructed and plotted against cumulative CO2 avoided (in Fig. 12). The profile of cumulative capital costs required for decarbonization of the site is also constructed (Fig. 13). When the same design options for CO2 reduction are applied to different processes or units those design options are applied first to units or processes having larger energy duties (before considering those with lower energy duties). For example when retrofitting the energy recovery systems, processes 1 to 4 are considered in sequence (with process 1 given the highest priority). Fig. 12 also indicates a number of different targets for CO2 avoided (20%, 40% and 60%) in the retrofit study which can help users with retrofit decision-making. It is worth noting here that all the possible retrofit options are considered when constructing these profiles, although some options may be eliminated at an early stage. These graphs generated by the screening procedure described here can be used for the top-level assessment of various design options reducing CO2 emissions. Hence, this methodology focuses
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Fig. 12. Case study: Decision-making for site-wide CO2 emissions reduction (I).
on the selection of appropriate retrofit technologies rather than providing design schemes or methods for the implementation at the site. Detailed process design for fuel switching, retrofit of energy recovery systems, or operational optimization of site utility systems would be required before any final decisions are made for this case study. 6. Conclusions and future work A new screening procedure has been developed with the aim to identify appropriate decarbonization retrofit options for industrial sites. This methodology systematically evaluates and ranks different options based on their costs and potential capacity for the reduction of CO2 emitted at a site. Utilizing this information the accumulated CO2 avoided versus the accumulated investment costs required can be calculated and shown graphically including multiple different retrofit options applied to multiple different sources
of CO2 in a site. Analysis of these graphs can be used to provide guidance for the “high-level” decision making process related to the selection of retrofit options. A case study has been presented to demonstrate the applicability of the proposed design methodology and to explain how the resulting analysis can be used to aid decision-making in practice. This provides conceptual understanding and physical insights regarding the implementation of carbon capture technology at process industries. Advances have been made in the development of design methodologies for the site-wide reduction of CO2 emissions. However, there are a few areas which need to be investigated in more detail as part of future work. As this study focuses on the screening and comparison of different options this procedure could be extended to include optimization of the selected combinations of retrofit option to meet emission targets and satisfy constraints on capital investment. In particular the rigorous design and optimization of the internal parameters in each retrofit should be carried
Fig. 13. Case study: Decision-making for site-wide CO2 emissions reduction (II).
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out including any interactions between different retrofits to confirm the feasibility of suggested combinations of retrofits. Acknowledgements This work was supported by the research fund of Hanyang University (HY-2013). References [1] B. Linnhoff, D.W. Townsend, D. Boland, G.F. Hewitt, B.E.A. Thomas, A.R. Guy, R.H. Marsland, A User Guide on Process Integration for the Efficient Use of Energy, IChemE, Rugby, 1982. [2] I.C. Kemp, Pinch Analysis and Process Integration: a User Guide on Process Integration of the Efficient Use of Energy, second ed., Elsevier, Oxford, 2007. [3] J. Klemes, F. Friedler, I. Bulatov, P. Varbanov, Sustainability in the Process Industry: Integration and Optimization, McGraw Hill, New York, 2010. [4] R. Smith, Chemical Process Design and Integration, Wiley, Chichester, 2005. [5] R. Smith, M. Jobson, L. Chen, Recent development in the retrofit of heat exchanger networks, Appl. Therm. Eng. 30 (2010) 2281e2289. [6] A. Mahmoud, M. Shuhaimi, M. Abdel Samed, A combined process integration and fuel switching strategy for emissions reduction in chemical process plants, Energy 34 (2009) 190e195. [7] B.J. Tiew, M. Shuhaimi, H. Hashim, Carbon emission reduction targeting through process integration and fuel switching with mathematical modeling, Appl. Energy 92 (2012) 686e693. [8] R.R. Tan, D.C.Y. Foo, Pinch analysis approach to carbon-constrained energy sector planning, Energy 33 (2007) 1422e1429.
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