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Research of production of CO2 from non-condensable gases in geothermal fluid and cost analysis
Geothermics 68 (2017) 1–8
Contents lists available at ScienceDirect
Geothermics journal homepage: www.elsevier.com/locate/geothermics
Research of production of CO2 from non-condensable gases in geothermal fluid and cost analysis Rasim Karabacak a , Fehim Mücasiro˘glu a , Mehmet Tan b,∗ , Sezgin Karabacak c a b c
Department of Mechanical Engineering, Faculty of Engineering, Pamukkale University, Denizli, Turkey Department of Electrical and Energy, Ula Ali Koc¸man Vocational High School, Mu˘gla Sıtkı Koc¸man University, Mu˘gla, Turkey Repuclic of Turkey Ministry of Energy and Natural Resources, Turkish Electricity Transmisson Company, I˙ zmir, Turkey
a r t i c l e
i n f o
Article history: Received 19 October 2016 Received in revised form 25 December 2016 Accepted 2 February 2017 Keywords: Production of carbon dioxide Geothermal fluid Dry ice Production cost Kızıldere geothermal area
a b s t r a c t In this research, we studied the techniques for production of CO2 by using non-condensable gas containing CO2 at a rate of 96%, obtained from the condenser of the thermal plant set up at Kızıldere Geothermal area. Moreover, CO2 ’s share in unit cost was analysed with regard to different production methods that are used for CO2 . On the other hand, the production of CO2 from geothermal fluid and by other methods have were analysed in terms of production cost, and it was found out that producing CO2 from geothermal fluid is 13–20% cheaper than other methods. © 2017 Elsevier Ltd. All rights reserved.
1. Introduction The oldest and the simplest method ever known for cooling is through use of ice and snow formed in the nature. However, today, cooling is possible regardless of time and place, thanks to technological developments in refrigerants and cooling cycles. Use of dry ice of CO2 has a special place among the cooling techniques. Dry ice of CO2 can be used easily for transportation not only of perishable foodstuff but also of human organs needed for transplantation as well as in many other areas such as cleaning of machines, plumbing, creating special affects etc. Because of its advantages, its importance has been increasing day by day while new areas for its use are constantly being investigated. Especially the research on use of dry ice of CO2 for industrial cleaning is gaining prominence. Cleaning with dry ice has major advantages over other methods of cleaning In this method, the dirt is removed from the surface by dry ice of CO2 particles which are accelerated by pressurized air and are crashed to the surface at a high speed of 300–900 m/s. Ice CO2 is sublimed after crashing the surface and it joins in the atmosphere in the gas form of CO2 (Ekren, 2006).
∗ Corresponding author. E-mail address: [email protected] (M. Tan). http://dx.doi.org/10.1016/j.geothermics.2017.02.004 0375-6505/© 2017 Elsevier Ltd. All rights reserved.
This method is also applied in many areas in the industry such as electric motors, conveyors, ovens, printers, pipes, press machinery, textile machinery, generators, transformers, bakery and control panels. Dry ice CO2 is not harmful to health. It has many outstanding features as it can cool 6–8 times faster than mechanical compression coolers, it prevents loss of colour, it has longer stock life and it does not leave any trace or stain. It is widely preferred for frigorific transportation since dry ice does not consume the moisture in the environment, thus it does not chance the shape of the food while preserving its quality. In addition to that carbon dioxide is widely used in beverage production and gas metal arc welding. There are many other uses of CO2 and the more widely usage areas are provided in reference (Barit Mining, 2008) in more detail. However, any study related with production of CO2 from non-condensable gases in geothermal fluid was not found in the literature. So, the aim of the present study is to investigate the production of CO2 from geothermal fluid and cost analysis. 2. Material Carbon dioxide is produced from stack gases which are obtained from the burning of petroleum, natural gas or coal. When petroleum, gas or coke is burned under a pressure of 13.5 atu, the combustion product of gas at 345 ◦ C will produce 10–15% CO2 . Moreover, the recycling rate of CO2 for fermentation process was indicated in reference (Bozan, 2000), it was indicated that it is possi-
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Table 1 Kızıldere geothermal power plant technic properties (Serpen and Türkmen, 2007). Part identification
Properties
Turbine pressure inlet Turbine temperature inlet Turbine pressure outlet Turbine temperature outlet Turbine outlet steam humidity Generation useful power Generation net power Compressor power Compressor capacity (for 1000 m3 /h) Suppressor power Condensate inlet temperature Condensate outlet temperature
3.5 bar 147 ◦ C 0.09 bar 51 ◦ C % 85 17.38 MWe 15 MWe 2.38 MWe 293.5 MWe 0.472 MWe 28 ◦ C 39 ◦ C
ble to obtain 0.27 L of alcohol (%95) and 0.220 kg CO2 from a starchy food such as corn. Indeed, the most important reason for the increase of CO2 level in atmosphere is the production of energy from fossil fuels. Level of CO2 released because of geothermal energy is lower than the level of CO2 released as a result of production of energy from fossil fuels (Cansever and Gülden, 2001). Kızıldere geothermal area is defined as a geothermal reservoir at 300–800 m with a temperature level of 196–212 ◦ C, containing 4500 ppm solid matter, with geothermal fluid having 1.5% CO2 (Satman et al., 2005; Serpen and Türkmen, 2005). The amount of CO2 obtained in this site is at a very high level, 750 g/kWh, hence all of this amount is not released to the atmosphere and an important portion is used for the production of CO2 and dry ice. As mentioned above the main resources of CO2 , where it can be obtained at an industrially sufficient level are as following: • Stack gases produced from the burning of solid, liquid and gas fuels containing carbon (%10–18 CO2 ) (Bozan, 2000). • Gases obtained as by products (%99 CO2 ) in the industry during the fermentation processes in the form of cracking of carbohydrates with alcohol and carbon dioxide (Bozan, 2000). • Gases obtained as by products in limekiln operations (%10–40 CO2 ) (Bozan, 2000). • Gases released by the condenser of the power plant producing electricity in a geothermal area (CO2 at 96%) (Serpen and Türkmen, 2007). 3. Method The technical characteristics of the Kızıldere geothermal power plant, which is located in Denizli Province of Turkey, is provided in Table 1. Steam turbine existing at the electric power plants in Kızıldere geothermal area is a double-flow turbine. This turbine, which is a multi-stage one, is connected with over a single shaft in order to maintain stability against the loads. The amount of water used in the condenser is 2375 kg/s and it is sprayed towards the steam (Serpen and Türkmen, 2007). Since they prevent vacuum forming within the condenser, non-condensable gases which pass through turbine and which contain 96% CO2 are taken away from condenser with a double cooled-screw compressor of 2.38 MW, having twostages (low and high pressure) and transferred to CO2 production unit. Water cooling tower is wet type and 4 fans, each with 110 kW, are employed for cooling purpose. For an isentropic heat drop of 465 kJ/K in geothermal steam turbine in Kızıldere, specific steam consumption is between 10.7 and 11.03 kg/kWh. When reservoir temperature is 200 ◦ C and discharge temperature is 48 ◦ C, useful heat and discharge heat are calculated as 120 kJ/kg and 540 kJ/kg respectively. Heat discharge rate of the power plant is 4.65, which is high because the resource tempera-
Table 2 The measurement values non-condensable gases extracted from the condenser of Kızıldere Geothermal Power Plant. Analyte
Precision (%RSD)
External Standart (% Recovery)
Sample Spike (%Recovery)
Carbon Dioxide Hydrogen Sulfide Ammonia Nitrogen Methane Hydrogen
1.9 NA 1.4 0.5 0.3 2.1
96.0 100.1 101.0 100.5 101.2 96.6
104.7 NA 100.3 NA NA NA
Precision : Percent Relative Standart Deviation of replicate sample analyses. External Standart: Percent Recovery of an independent audit standard analysed against calibration standarts (measured/known x 100). Sample Spike: Percent Recovery of an known quantity of standart added to sample (measured/theoretical × 100). NA: Not Applicable.
ture is low. On the other hand, in fossil power plants, heat discharge rate is around 1.1 (Serpen and Türkmen, 2007). In power plants, like Kızıldere, which work with geothermal fluids with high gas content, the existence of gas within the condenser is an important problem that affects the power production negatively. The performance of the turbine is dependent upon the back-pressure conserved inside the turbine. Back-pressure is equal to the sum of partial pressures of steam and non-condensable gases usually CO2 . These raw gases extracted from the condenser of Kızıldere Geothermal Power Plant is given in Table 2. Partial steam pressure is the saturation pressure that corresponds to the exit temperature. CO2 partial pressure, however, is dependent on its mass. For Kızıldere Power Plant, CO2 partial pressure is calculated as 0.3 bar (Serpen and Türkmen, 2007). Since the existing energy of CO2 is lower than the energy of the water steam, the specific production of the turbine decreases as the ratio of the carbon dioxide increases. However the total production of the turbine increases due to increase in the quantity of CO2 . The increase due to expansion of CO2 in the turbine of Kızıldere Geothermal power plant is around 5%. On the other hand, there is a 13% reduction in power production due to CO2 . In addition to that, as 773 kW energy is used for compressor, the total loss of energy in power production stemming from CO2 is around 12%. 96% CO2 contained in the raw gas extracted from the condenser of the thermal power station is sent to the CO2 production plant, where it is first transformed into liquid CO2 . It is then, if desired so, converted into dry ice and marketed as an industrial product. Surface Equipment at Kızıldere Geothermal Power Plant are shown in Fig. 1. Kızıldere is a classic single-flash unit geothermal power plant with a capacity of 17.8 MWe. Its net production power is 15 Mwe. The carbon dioxide level in the raw gas obtained from the condenser is 96%. It is also possible to produce CO2 directly from the fluid taken from the wells in case the power plant is not working. But because of the production costs, raw gas is taken from the condenser as long as the plant is working. If the production is made from the fluid directly taken from the wells, the fluid steam is passed through condenser; water steam is condensed and the gas is directed inside from below the showering unit. In this way, dust and other particles inside the CO2 is taken away by water (Karbogas Inc., 2007). 3.1. Liquide carbon-dioxide production The layout of the CO2 production unit at Kızıldere geothermal site is provided in Fig. 2. The raw gas taken from the condenser of the thermal power plant is forwarded towards the CO2 production facility with the help of a blower motor at a speed of 5 ton/h and at a pressure of 0.1 bar. The raw gas, whose entry quality control is made with Orsat
R. Karabacak et al. / Geothermics 68 (2017) 1–8
3
Fig. 1. Surface Equipment at Kızıldere Geothermal Power Plant (Serpen and Türkmen, 2007).
apparatus, is subjected to a process of pre-condensation so that the compressors can work with an appropriate level of efficiency. As a result of pre-condensation process carried out at the Blower, the gas pressure is increased to a level between 0.2 and 0.6 bar. The gas whose pressure has been increased to the desired level as a result of pre-condensation is sent to horizontal water-cooled E-00 heat exchanger for the pre-cooling process. Here the temperature of the raw gas is decreased from 80 ◦ C to 40 ◦ C. The temperature of the gas cooled as a result of this process could be 10 ◦ C lower or higher depending on the season of the year, whether it is summer or winter (Karbogas Inc., 2007). Once the temperature of the gas is reduced in E-00 heat exchanger, the water steam inside the gas is condensed and taken from S-00 separator by the valve with the help of the operator. The gas which exits S-00 separator at a temperature of 40 ◦ C is further cooled down to 35 ◦ C in E-01 heat exchanger. The temperature of the gas exiting E-01 heat exchanger could vary, depending on the weather conditions. In winter, it could be 25 ◦ C (Karbogas Inc., 2007). Once the temperature of the gas is further decreased after E-01 heat exchanger, water steam is automatically taken out through S-01 separator. After this pre-treatment, the gas, at entry conditions of 35 ◦ C and 0.2–0.35 bar, is compressed up to the levels of pressure of 3.8 bar and temperature of 70–95 ◦ C in C-01 piston type low pressure compressor. The temperature of the exiting gas is further decreased to 32–35 ◦ C in E-02 ammonia-cooled heat exchanger. The water steam which is condensed here is taken out through S-02 separator. The gas exiting S-02 separator enters into C-02 screw-type high pressure compressor, where the heat and the pressure are increased to the levels of 75–100 ◦ C and 19–22 bar respectively. The variation of the temperature and the pressure levels of the gas exiting the high pressure compressor is due to seasonal changes. The gas exiting the high pressure compressor may contain some oil. Therefore, in order to remove this oil, the gas is directed towards DS-06 separator and the oil contained here is again directed to suction of C-02 compressor. While the oil is directed toward com-
pressor the pressure difference in return should be less than 1 bar. The gas which exits C-02 high pressure compressor is sent to E-02 ammonia-cooled heat exchanger in order to make it cooler. Here the gas is cooled from 100 to 120 ◦ C down to a temperature level between 25 and 45 ◦ C and condensed. From here the gas moves to the showering tower for cleaning at a temperature between 25 and 45 ◦ C depending on seasonal changes. The gas enters into the tower from bottom and pass through the sprinkling water and gets out of the tower at the top. During this process, dust and some other particles, some substances such as alcohol and ether and some H2 S are kept by water and taken out of the gas. The water is given to the system by a pump with a flow rate of 1 m3 /h. The water that could be condensed in the power plant is taken away through S-03 separator by a valve. The gas leaving showering tower at a temperature between 28 and 35 ◦ C enters into D-17 sulfatreat tower to remove the sulphur compounds. The sulfatreat substance inside the tower catches H2 S concentration inside the gas to a great extent. The level of H2 S value inside the gas exiting the tower is measured by a sulphur analyser and it is ensured that H2 S value does not exceed 25 ppm (Mücasiro˘glu, 2008). The gas is passed through D-18 and D-19 towers which are serially connected and contain solvent solutions of potassium permanganate (KMnO4 ) and sodium carbonate ((Na2 CO3 ) and H2 S and SO2 inside the gas are contained. It is targeted that the sulphur level in the gas is lower than 100 ppb. After gas passes through D-18 and D-19 towers, liquid chemical solution (KMnO4 ) is held in S-04 separator and thrown out from the valves. The gas exiting D-18 tower is cooled in E-05 heat exchanger. During this process, the temperature of the gas is reduced and a great amount of water steam is condensed. The gas which enters into E-05 heat exchanger at a temperature of 30 ◦ C, leaves it at a level of temperature between 7 and 12 ◦ C. Ammonia which enters into E-05 heat exchanger at a pressure of 12 bar leaves it at a pressure of 4–4.5 bar. Water steam condensed
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Fig. 2. Flowchart for CO2 production.
as a result of the reduction in temperature of the gas is thrown out automatically from the system through S-05 separator. The gas exiting S-05 separator goes to activated alumina unit D-06A and D06B. Activated alumina is a chemical obtained by controlled heating of aluminium hydroxide and removal of water therein. Activated alumina is commonly used for adsorption and catalysis processes. Therefore, the last remaining moisture in the system is contained through adsorption process in D–06A and D–06B towers. At the exit of the tower, the state of the gas is measured with moisture analyser and it is ensured that moisture rate is lower than 20 ppm. Activated alumina particles and dust which are worn away by each other during the passage are contained with the passage of the
gas through F-01 Filter. The pressure difference in the filter should not be less than 0.5 bar. Here the purpose is to obtain gas which do not contain dust and moisture. After passing through activated alumina towers and the filter, gas comes to D-04A and D–04 B towers containing activated carbon with the purpose of removing the last remaining of oil, benzene and odours. After this process, it must be ensured that hydrocarbon level in the gas is less than 20 ppm. Activated carbon particles and dust, which is worn away during the passage of the gas, are also contained in F-20 filter. The pressure difference in the filter should not be more than 0.5 bar. This can be determined by measures made over previous and subsequent pressure values by a nanometre. Gas exiting this area is directed towards E-06 heat exchanger in order to reduce the temperature and per-
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form the boiling. Liquid CO2 which is at a temperature between −8 and −18 ◦ C at the bottom of the E-60 heat exchanger (reboiler) is heated with gas and boiled and is purified from hydro carbon impurities (contamination). The gas at the exit of E-60 heat exchanger has a pressure level of 17.5 bar. Then the gas is directed to E-07 heat exchanger for heat reduction and liquidation. In E-07 heat exchanger, the CO2 gas is cooled down to −20 to −30 ◦ C and liquefied to a great extent by using liquid ammoniac with a temperature of −31 ◦ C. After leaving E-07 heat exchanger, CO2 enters into D-14 scrapper/distillation tower of the reboiler. CO2 is divided into droplets in D-14 tower and descends to the bottom of the reboiler. Here the CO2 , which gets down D-14 tower by being liquefied, is accumulated in a controlled manner. CO2 , which is decomposed from CH4 , O2 , N2 , H2 , He and hydrocarbons goes down to S-08 separator by passing through E-08 heat exchanger. At the end of the process, it is necessary that the total hydrocarbon rate within the gas should be less than 20 ppm (Mücasiro˘glu, 2008). Before being sent to the storage tanks, liquid CO2 is sent to E-09 heat exchanger for final heat stabilisation. Here it is cooled down to a temperature level between −23 and −28 ◦ C and then it is sent to storage tanks. Sulphur, hydrocarbon, NOx and moisture analysis are carried out on the final product that will be sent to storage tanks. In the analyses, total hydrocarbon value should be less than 15 ppm while total sulphur, total moisture and NOx values should be less than 80, 15 and 0.8 ppm respectively (Mücasiro˘glu, 2008). Hydrocarbons collected from CO2 is taken out through S-08 separator. A small amount of CO2 is taken from the lower part of S-08 to the outside of E-08 heat exchanger in order to exchange heat. CO2 passing through E-08 is cooled down to −28 ◦ C. In this process, the purpose is to make use of liquid CO2 and to throw away hydrocarbons. CO2 gas which is decomposed from liquid CO2 in D-14 reboiler tower and other material in the gas phase (CH4 , O2 , N2 , etc.) are taken to E-08 heat exchanger and processed here once more. Here, liquid CO2 is decomposed from these unwanted substances, which are emitted to the atmosphere. The collected CO2 is sent to the storage tank as shown in Fig. 2. CO2 within the storage tanks are both in gas and liquid phases. When the liquid CO2 is continuously take away from the tank, the gas pressure increases. Since the cooling unit is adjusted at a level between 16 and 22 bar, once the pressure increases, it steps in by condensing the gas phase and secures the system. In the opposite case, if the use of gas is higher, the pressure decreases and there appears a risk of frost. In that case, the electrical heaters start working and increase the pressure to the desired level. Moreover, there is a security valve over the top of the each deposit tank. This valve ensures the security
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Table 3 Characteristic pressure and temperature values for devices used in the production of CO2 . Nokta
1
2
3
4
5
6
7
8
P (bar) T (◦ C) Nokta P (bar) T (◦ C)
0.1 39 9 19 40
0.35 80 10 19 30
0.30 40 11 18.5 30
0.26 35 12 18.5 10
4.2 90 13 17.5 10
4.2 42 14 17.5 −14
20 95 15 17.5 −25
19 95 16 17.5 −27
of the system by opening when interior pressure reaches to 26 bar and it is closed once the pressure is lowered. The system diagram is provided in Fig. 3. Temperature and Pressure shifts in every step at an site producing CO2 from geothermal energy, from the compression of the raw gas in the blower (1) to the storage tank (16) are shown collectively in Fig. 4 and Table 3. 3.2. Dry ice production Liquid carbon dioxide, which is stored in special tanks with ideal storage conditions for dry ice production with a temperature level between −23 and −28 ◦ C and pressure level between 16 and 19 bar, is fed into the dry ice machine as shown in Fig. 5. Liquid carbon dioxide is released downwards from the above of the machine block. The liquid carbon dioxide suddenly takes the form of snow with the effect of decreasing temperature and pressure under the existing atmospheric conditions. At this instance, a certain amount of CO2 takes the gas form and it is taken inside from the above of the machine block and sent back to the coolers to be condensed again. In order to create vibration, a vibrator is placed over the block. The substance in the form of snow which is taken down with the help of the vibrator is accumulated over the apparatus which provides compression and formation. Accumulated snow is compressed and shaped with the help of a hydraulic piston and a gate which is opened and closed with hydraulic pressure. The resultant dry ice is cut into desired dimensions with chrome saw and stored and transported in boxes made of special Styrofoam. Dry Ice machine is shown schematically in Fig. 5. 4. Cost calculation for production of CO2 from geothermal fluid 4.1. Cost of raw gas Annual capacity of CO2 production plant at Kızıldere Geothermal site is 30,000 ton (Mücasiro˘glu, 2008). For production of 1 kg CO2 is 1.176 kg raw gas is required (Karbogas Inc., 2007). Accordingly, for production of 1 t CO2, we need,
Table 4 The amounts of materials and supplies used in production of a ton liguid CO2 and their share in production cost (%). Item no
Consumable type
Amount
Unit price
Totally $/t CO2
% Rate
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Crude gas (m3 ) Electric consumption KMnO4 NaCO3 Sülfatreat Activated alümina Activated carbon Ammonia Oil Water Staff, insurance, service, mess Subtotal Cost in use Totally
735.294 400 kWh 3 kg 2.4 kg 2.4 kg 0.025 kg 0.10 kg 0.33 kg 0.266 lt 2.5 m3 – – Subtotal cost × %20
0.63 $/m3 0.1417 $/kg 1.5$/kg 0.4 $/kg 1.5 $/kg 2.75 $/kg 23.62 $/kg 1.26 $/kg 1.2 $/kg 1.102 $/m3 – –
4.63 56.68 4.50 0.96 3.60 0.069 2.362 0.42 0.32 2.755 63.00 139.23 27.84 167
2.77 33.94 2.69 0.57 2.16 0.04 1.41 0.25 0.19 1.65 37.72 16.61
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Fig. 3. Cooling and heating unit of CO2 storage tank.
mgas = 1000 × 1.176 = 1176 kg raw gas. Density of 1 m3 raw gas: g = 1.6 kg/m3 (Mücasiro˘glu, 2008). Therefore, the required amount of gas is 735 m3 . As 1 m3 raw gas costs 0.63 cents (Karbogas Inc., 2007) the cost of raw gas needed for production of 1 t CO2 is: ma = 4.63 $/t CO2 . In addition to that, other costs of production; electricity consumption, chemicals and wages, insurance, meals and transportation expenses for personnel working in the plant, are shown in As it can be seen in Table 4, energy consumption of the generators used in production has the biggest share in cost of production (33.94%). The calculation are made on the assumption that CO2 is provided from the condenser of the thermal power plant. In case, he power plant does not work or the raw gas coming from power plant is not sufficient, there will be some increase in the cost of production since the production will be made from the gas that will be taken directly from the reservoir.
4.2. Other costs in the operation It is calculated as 20% of total cost. Hence, the production cost of 1 t CO2 is found to be 167 ($/t).
4.3. The expenses mentioned above do not include tax and transportation cost Tax is paid at a rate of 40% over the profit. Transportation cost is calculated by the total length of transportation expressed in km (round trip including the return) by 0.5 (Mücasiro˘glu, 2008). A formula including these two variables shows the sales price as following: P = [2004 + 8D]/
20 K
−8
$/t CO2
(1)
where;P: sales price ($/t CO2 ) D: total length of transportation (including return) (km)K: Coefficient that also include profitability ratio 5. Results and conclusions In thermal power plants, like Kızıldere, which operate by using geothermal fluids containing to a great extent (1.5–2.5% of total weight) non-condensable CO2 , if the non-condensable gases are not removed from the condenser, they results in an important problem that effect power production negatively. The performance of the steam turbine is dependent on the back pressure at the turbine outlet. Partial pressure of CO2 is calculated as 0.3 bar for Kızıldere power plant. At Kızıldere geothermal power
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Fig. 4. Pressure and temperature values at characteristic points for devices used in the production of CO2 .
Fig. 5. Schematic presentation of dry ice production machine.
plant, the power increase stemming from the expansion of CO2 in the turbine is around 5%, while loss in power production due to partial pressure is 13%. In addition to, 773 kW energy is used for compressor. As a result, the total loss in energy production because of CO2 is around 12%.
Instead of throwing the gas out into the atmosphere by using compressor, it is send to the CO2 production unit, located in the power plant area, where liquid CO2 and dry ice are produced as industrial products. According to the findings of the study:
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1) The production cost of 1 t CO2 by using raw gas obtained from the condenser of the thermal power plant at Kızıldere geothermal area is calculated as $ 167; 2) The cost of production of the same amount of CO2 with other alternative methods varies between $ 190–200; 3) The production of CO2 from geothermal fluid is 13–20% cheaper compared to other methods; 4) The personnel expenses has the biggest share in total cost of production (37.7%) and it is followed by electricity expense (34%) (Table 3); 5) The sales price for 1 t CO2 (P) is determined as following:
P = [2004 + 8D]/
20 K
−8
$/t CO2
(where K: coefficient including profitability ratio; D: total transportation including return) 6) The cost of CO2 corresponds to the 1% of total cost in beverage production and 0.5% of the total cost in gas metal arc welding.
Acknowledgements We would like to thank the Repuclic of Turkey Ministry of Energy and Natural Resources, Karbogas Company and Pamukkale University Institute of Science for supporting this work. References Barit Mining Turk Corporation Limited, 2008. Available from: http://www. baritmaden.com/karbondioxitco2. Bozan, B., 2000. Available from: http://home.anadolu.edu.tr/∼bozan/KIMTEK.htm. Cansever, I˙ ., Gülden, S., 2001. Geotermal Energy. SDÜ Environment Engineering Department. Ekren, O., 2006. Cleaning with dry ice Application, The World of Cooling, vol. 34, 35–42. Karbogas Inc, 2007. Dry Ice Production Process, 1–10. Mücasiro˘glu, F., 2008. Dry Ice Production from Geotermal Energy, Unpublished M.Sc Thesies. Pamukkale University, Institute of Sciences, Denizli, Turkey. Satman, A., Sarak, H., Onur, M., Korkmaz, E.D., 2005. Modeling of production/reinjection behavior of the Kizildere Geothermal Field by a 2-layer geothermal reservoir lumped parameter model. In: Proceedings of the World Geothermal Congress 2005, Antalya, Turkey, 24–29 April. Serpen, U., Türkmen, N., 2007. 23rd annual performance evaluation of kizildere geothermal power plant TESKON. In: Geotermal Energy Conference, I˙ stanbul, pp. 219–228.
Contents lists available at ScienceDirect
Geothermics journal homepage: www.elsevier.com/locate/geothermics
Research of production of CO2 from non-condensable gases in geothermal fluid and cost analysis Rasim Karabacak a , Fehim Mücasiro˘glu a , Mehmet Tan b,∗ , Sezgin Karabacak c a b c
Department of Mechanical Engineering, Faculty of Engineering, Pamukkale University, Denizli, Turkey Department of Electrical and Energy, Ula Ali Koc¸man Vocational High School, Mu˘gla Sıtkı Koc¸man University, Mu˘gla, Turkey Repuclic of Turkey Ministry of Energy and Natural Resources, Turkish Electricity Transmisson Company, I˙ zmir, Turkey
a r t i c l e
i n f o
Article history: Received 19 October 2016 Received in revised form 25 December 2016 Accepted 2 February 2017 Keywords: Production of carbon dioxide Geothermal fluid Dry ice Production cost Kızıldere geothermal area
a b s t r a c t In this research, we studied the techniques for production of CO2 by using non-condensable gas containing CO2 at a rate of 96%, obtained from the condenser of the thermal plant set up at Kızıldere Geothermal area. Moreover, CO2 ’s share in unit cost was analysed with regard to different production methods that are used for CO2 . On the other hand, the production of CO2 from geothermal fluid and by other methods have were analysed in terms of production cost, and it was found out that producing CO2 from geothermal fluid is 13–20% cheaper than other methods. © 2017 Elsevier Ltd. All rights reserved.
1. Introduction The oldest and the simplest method ever known for cooling is through use of ice and snow formed in the nature. However, today, cooling is possible regardless of time and place, thanks to technological developments in refrigerants and cooling cycles. Use of dry ice of CO2 has a special place among the cooling techniques. Dry ice of CO2 can be used easily for transportation not only of perishable foodstuff but also of human organs needed for transplantation as well as in many other areas such as cleaning of machines, plumbing, creating special affects etc. Because of its advantages, its importance has been increasing day by day while new areas for its use are constantly being investigated. Especially the research on use of dry ice of CO2 for industrial cleaning is gaining prominence. Cleaning with dry ice has major advantages over other methods of cleaning In this method, the dirt is removed from the surface by dry ice of CO2 particles which are accelerated by pressurized air and are crashed to the surface at a high speed of 300–900 m/s. Ice CO2 is sublimed after crashing the surface and it joins in the atmosphere in the gas form of CO2 (Ekren, 2006).
∗ Corresponding author. E-mail address: [email protected] (M. Tan). http://dx.doi.org/10.1016/j.geothermics.2017.02.004 0375-6505/© 2017 Elsevier Ltd. All rights reserved.
This method is also applied in many areas in the industry such as electric motors, conveyors, ovens, printers, pipes, press machinery, textile machinery, generators, transformers, bakery and control panels. Dry ice CO2 is not harmful to health. It has many outstanding features as it can cool 6–8 times faster than mechanical compression coolers, it prevents loss of colour, it has longer stock life and it does not leave any trace or stain. It is widely preferred for frigorific transportation since dry ice does not consume the moisture in the environment, thus it does not chance the shape of the food while preserving its quality. In addition to that carbon dioxide is widely used in beverage production and gas metal arc welding. There are many other uses of CO2 and the more widely usage areas are provided in reference (Barit Mining, 2008) in more detail. However, any study related with production of CO2 from non-condensable gases in geothermal fluid was not found in the literature. So, the aim of the present study is to investigate the production of CO2 from geothermal fluid and cost analysis. 2. Material Carbon dioxide is produced from stack gases which are obtained from the burning of petroleum, natural gas or coal. When petroleum, gas or coke is burned under a pressure of 13.5 atu, the combustion product of gas at 345 ◦ C will produce 10–15% CO2 . Moreover, the recycling rate of CO2 for fermentation process was indicated in reference (Bozan, 2000), it was indicated that it is possi-
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Table 1 Kızıldere geothermal power plant technic properties (Serpen and Türkmen, 2007). Part identification
Properties
Turbine pressure inlet Turbine temperature inlet Turbine pressure outlet Turbine temperature outlet Turbine outlet steam humidity Generation useful power Generation net power Compressor power Compressor capacity (for 1000 m3 /h) Suppressor power Condensate inlet temperature Condensate outlet temperature
3.5 bar 147 ◦ C 0.09 bar 51 ◦ C % 85 17.38 MWe 15 MWe 2.38 MWe 293.5 MWe 0.472 MWe 28 ◦ C 39 ◦ C
ble to obtain 0.27 L of alcohol (%95) and 0.220 kg CO2 from a starchy food such as corn. Indeed, the most important reason for the increase of CO2 level in atmosphere is the production of energy from fossil fuels. Level of CO2 released because of geothermal energy is lower than the level of CO2 released as a result of production of energy from fossil fuels (Cansever and Gülden, 2001). Kızıldere geothermal area is defined as a geothermal reservoir at 300–800 m with a temperature level of 196–212 ◦ C, containing 4500 ppm solid matter, with geothermal fluid having 1.5% CO2 (Satman et al., 2005; Serpen and Türkmen, 2005). The amount of CO2 obtained in this site is at a very high level, 750 g/kWh, hence all of this amount is not released to the atmosphere and an important portion is used for the production of CO2 and dry ice. As mentioned above the main resources of CO2 , where it can be obtained at an industrially sufficient level are as following: • Stack gases produced from the burning of solid, liquid and gas fuels containing carbon (%10–18 CO2 ) (Bozan, 2000). • Gases obtained as by products (%99 CO2 ) in the industry during the fermentation processes in the form of cracking of carbohydrates with alcohol and carbon dioxide (Bozan, 2000). • Gases obtained as by products in limekiln operations (%10–40 CO2 ) (Bozan, 2000). • Gases released by the condenser of the power plant producing electricity in a geothermal area (CO2 at 96%) (Serpen and Türkmen, 2007). 3. Method The technical characteristics of the Kızıldere geothermal power plant, which is located in Denizli Province of Turkey, is provided in Table 1. Steam turbine existing at the electric power plants in Kızıldere geothermal area is a double-flow turbine. This turbine, which is a multi-stage one, is connected with over a single shaft in order to maintain stability against the loads. The amount of water used in the condenser is 2375 kg/s and it is sprayed towards the steam (Serpen and Türkmen, 2007). Since they prevent vacuum forming within the condenser, non-condensable gases which pass through turbine and which contain 96% CO2 are taken away from condenser with a double cooled-screw compressor of 2.38 MW, having twostages (low and high pressure) and transferred to CO2 production unit. Water cooling tower is wet type and 4 fans, each with 110 kW, are employed for cooling purpose. For an isentropic heat drop of 465 kJ/K in geothermal steam turbine in Kızıldere, specific steam consumption is between 10.7 and 11.03 kg/kWh. When reservoir temperature is 200 ◦ C and discharge temperature is 48 ◦ C, useful heat and discharge heat are calculated as 120 kJ/kg and 540 kJ/kg respectively. Heat discharge rate of the power plant is 4.65, which is high because the resource tempera-
Table 2 The measurement values non-condensable gases extracted from the condenser of Kızıldere Geothermal Power Plant. Analyte
Precision (%RSD)
External Standart (% Recovery)
Sample Spike (%Recovery)
Carbon Dioxide Hydrogen Sulfide Ammonia Nitrogen Methane Hydrogen
1.9 NA 1.4 0.5 0.3 2.1
96.0 100.1 101.0 100.5 101.2 96.6
104.7 NA 100.3 NA NA NA
Precision : Percent Relative Standart Deviation of replicate sample analyses. External Standart: Percent Recovery of an independent audit standard analysed against calibration standarts (measured/known x 100). Sample Spike: Percent Recovery of an known quantity of standart added to sample (measured/theoretical × 100). NA: Not Applicable.
ture is low. On the other hand, in fossil power plants, heat discharge rate is around 1.1 (Serpen and Türkmen, 2007). In power plants, like Kızıldere, which work with geothermal fluids with high gas content, the existence of gas within the condenser is an important problem that affects the power production negatively. The performance of the turbine is dependent upon the back-pressure conserved inside the turbine. Back-pressure is equal to the sum of partial pressures of steam and non-condensable gases usually CO2 . These raw gases extracted from the condenser of Kızıldere Geothermal Power Plant is given in Table 2. Partial steam pressure is the saturation pressure that corresponds to the exit temperature. CO2 partial pressure, however, is dependent on its mass. For Kızıldere Power Plant, CO2 partial pressure is calculated as 0.3 bar (Serpen and Türkmen, 2007). Since the existing energy of CO2 is lower than the energy of the water steam, the specific production of the turbine decreases as the ratio of the carbon dioxide increases. However the total production of the turbine increases due to increase in the quantity of CO2 . The increase due to expansion of CO2 in the turbine of Kızıldere Geothermal power plant is around 5%. On the other hand, there is a 13% reduction in power production due to CO2 . In addition to that, as 773 kW energy is used for compressor, the total loss of energy in power production stemming from CO2 is around 12%. 96% CO2 contained in the raw gas extracted from the condenser of the thermal power station is sent to the CO2 production plant, where it is first transformed into liquid CO2 . It is then, if desired so, converted into dry ice and marketed as an industrial product. Surface Equipment at Kızıldere Geothermal Power Plant are shown in Fig. 1. Kızıldere is a classic single-flash unit geothermal power plant with a capacity of 17.8 MWe. Its net production power is 15 Mwe. The carbon dioxide level in the raw gas obtained from the condenser is 96%. It is also possible to produce CO2 directly from the fluid taken from the wells in case the power plant is not working. But because of the production costs, raw gas is taken from the condenser as long as the plant is working. If the production is made from the fluid directly taken from the wells, the fluid steam is passed through condenser; water steam is condensed and the gas is directed inside from below the showering unit. In this way, dust and other particles inside the CO2 is taken away by water (Karbogas Inc., 2007). 3.1. Liquide carbon-dioxide production The layout of the CO2 production unit at Kızıldere geothermal site is provided in Fig. 2. The raw gas taken from the condenser of the thermal power plant is forwarded towards the CO2 production facility with the help of a blower motor at a speed of 5 ton/h and at a pressure of 0.1 bar. The raw gas, whose entry quality control is made with Orsat
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Fig. 1. Surface Equipment at Kızıldere Geothermal Power Plant (Serpen and Türkmen, 2007).
apparatus, is subjected to a process of pre-condensation so that the compressors can work with an appropriate level of efficiency. As a result of pre-condensation process carried out at the Blower, the gas pressure is increased to a level between 0.2 and 0.6 bar. The gas whose pressure has been increased to the desired level as a result of pre-condensation is sent to horizontal water-cooled E-00 heat exchanger for the pre-cooling process. Here the temperature of the raw gas is decreased from 80 ◦ C to 40 ◦ C. The temperature of the gas cooled as a result of this process could be 10 ◦ C lower or higher depending on the season of the year, whether it is summer or winter (Karbogas Inc., 2007). Once the temperature of the gas is reduced in E-00 heat exchanger, the water steam inside the gas is condensed and taken from S-00 separator by the valve with the help of the operator. The gas which exits S-00 separator at a temperature of 40 ◦ C is further cooled down to 35 ◦ C in E-01 heat exchanger. The temperature of the gas exiting E-01 heat exchanger could vary, depending on the weather conditions. In winter, it could be 25 ◦ C (Karbogas Inc., 2007). Once the temperature of the gas is further decreased after E-01 heat exchanger, water steam is automatically taken out through S-01 separator. After this pre-treatment, the gas, at entry conditions of 35 ◦ C and 0.2–0.35 bar, is compressed up to the levels of pressure of 3.8 bar and temperature of 70–95 ◦ C in C-01 piston type low pressure compressor. The temperature of the exiting gas is further decreased to 32–35 ◦ C in E-02 ammonia-cooled heat exchanger. The water steam which is condensed here is taken out through S-02 separator. The gas exiting S-02 separator enters into C-02 screw-type high pressure compressor, where the heat and the pressure are increased to the levels of 75–100 ◦ C and 19–22 bar respectively. The variation of the temperature and the pressure levels of the gas exiting the high pressure compressor is due to seasonal changes. The gas exiting the high pressure compressor may contain some oil. Therefore, in order to remove this oil, the gas is directed towards DS-06 separator and the oil contained here is again directed to suction of C-02 compressor. While the oil is directed toward com-
pressor the pressure difference in return should be less than 1 bar. The gas which exits C-02 high pressure compressor is sent to E-02 ammonia-cooled heat exchanger in order to make it cooler. Here the gas is cooled from 100 to 120 ◦ C down to a temperature level between 25 and 45 ◦ C and condensed. From here the gas moves to the showering tower for cleaning at a temperature between 25 and 45 ◦ C depending on seasonal changes. The gas enters into the tower from bottom and pass through the sprinkling water and gets out of the tower at the top. During this process, dust and some other particles, some substances such as alcohol and ether and some H2 S are kept by water and taken out of the gas. The water is given to the system by a pump with a flow rate of 1 m3 /h. The water that could be condensed in the power plant is taken away through S-03 separator by a valve. The gas leaving showering tower at a temperature between 28 and 35 ◦ C enters into D-17 sulfatreat tower to remove the sulphur compounds. The sulfatreat substance inside the tower catches H2 S concentration inside the gas to a great extent. The level of H2 S value inside the gas exiting the tower is measured by a sulphur analyser and it is ensured that H2 S value does not exceed 25 ppm (Mücasiro˘glu, 2008). The gas is passed through D-18 and D-19 towers which are serially connected and contain solvent solutions of potassium permanganate (KMnO4 ) and sodium carbonate ((Na2 CO3 ) and H2 S and SO2 inside the gas are contained. It is targeted that the sulphur level in the gas is lower than 100 ppb. After gas passes through D-18 and D-19 towers, liquid chemical solution (KMnO4 ) is held in S-04 separator and thrown out from the valves. The gas exiting D-18 tower is cooled in E-05 heat exchanger. During this process, the temperature of the gas is reduced and a great amount of water steam is condensed. The gas which enters into E-05 heat exchanger at a temperature of 30 ◦ C, leaves it at a level of temperature between 7 and 12 ◦ C. Ammonia which enters into E-05 heat exchanger at a pressure of 12 bar leaves it at a pressure of 4–4.5 bar. Water steam condensed
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Fig. 2. Flowchart for CO2 production.
as a result of the reduction in temperature of the gas is thrown out automatically from the system through S-05 separator. The gas exiting S-05 separator goes to activated alumina unit D-06A and D06B. Activated alumina is a chemical obtained by controlled heating of aluminium hydroxide and removal of water therein. Activated alumina is commonly used for adsorption and catalysis processes. Therefore, the last remaining moisture in the system is contained through adsorption process in D–06A and D–06B towers. At the exit of the tower, the state of the gas is measured with moisture analyser and it is ensured that moisture rate is lower than 20 ppm. Activated alumina particles and dust which are worn away by each other during the passage are contained with the passage of the
gas through F-01 Filter. The pressure difference in the filter should not be less than 0.5 bar. Here the purpose is to obtain gas which do not contain dust and moisture. After passing through activated alumina towers and the filter, gas comes to D-04A and D–04 B towers containing activated carbon with the purpose of removing the last remaining of oil, benzene and odours. After this process, it must be ensured that hydrocarbon level in the gas is less than 20 ppm. Activated carbon particles and dust, which is worn away during the passage of the gas, are also contained in F-20 filter. The pressure difference in the filter should not be more than 0.5 bar. This can be determined by measures made over previous and subsequent pressure values by a nanometre. Gas exiting this area is directed towards E-06 heat exchanger in order to reduce the temperature and per-
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form the boiling. Liquid CO2 which is at a temperature between −8 and −18 ◦ C at the bottom of the E-60 heat exchanger (reboiler) is heated with gas and boiled and is purified from hydro carbon impurities (contamination). The gas at the exit of E-60 heat exchanger has a pressure level of 17.5 bar. Then the gas is directed to E-07 heat exchanger for heat reduction and liquidation. In E-07 heat exchanger, the CO2 gas is cooled down to −20 to −30 ◦ C and liquefied to a great extent by using liquid ammoniac with a temperature of −31 ◦ C. After leaving E-07 heat exchanger, CO2 enters into D-14 scrapper/distillation tower of the reboiler. CO2 is divided into droplets in D-14 tower and descends to the bottom of the reboiler. Here the CO2 , which gets down D-14 tower by being liquefied, is accumulated in a controlled manner. CO2 , which is decomposed from CH4 , O2 , N2 , H2 , He and hydrocarbons goes down to S-08 separator by passing through E-08 heat exchanger. At the end of the process, it is necessary that the total hydrocarbon rate within the gas should be less than 20 ppm (Mücasiro˘glu, 2008). Before being sent to the storage tanks, liquid CO2 is sent to E-09 heat exchanger for final heat stabilisation. Here it is cooled down to a temperature level between −23 and −28 ◦ C and then it is sent to storage tanks. Sulphur, hydrocarbon, NOx and moisture analysis are carried out on the final product that will be sent to storage tanks. In the analyses, total hydrocarbon value should be less than 15 ppm while total sulphur, total moisture and NOx values should be less than 80, 15 and 0.8 ppm respectively (Mücasiro˘glu, 2008). Hydrocarbons collected from CO2 is taken out through S-08 separator. A small amount of CO2 is taken from the lower part of S-08 to the outside of E-08 heat exchanger in order to exchange heat. CO2 passing through E-08 is cooled down to −28 ◦ C. In this process, the purpose is to make use of liquid CO2 and to throw away hydrocarbons. CO2 gas which is decomposed from liquid CO2 in D-14 reboiler tower and other material in the gas phase (CH4 , O2 , N2 , etc.) are taken to E-08 heat exchanger and processed here once more. Here, liquid CO2 is decomposed from these unwanted substances, which are emitted to the atmosphere. The collected CO2 is sent to the storage tank as shown in Fig. 2. CO2 within the storage tanks are both in gas and liquid phases. When the liquid CO2 is continuously take away from the tank, the gas pressure increases. Since the cooling unit is adjusted at a level between 16 and 22 bar, once the pressure increases, it steps in by condensing the gas phase and secures the system. In the opposite case, if the use of gas is higher, the pressure decreases and there appears a risk of frost. In that case, the electrical heaters start working and increase the pressure to the desired level. Moreover, there is a security valve over the top of the each deposit tank. This valve ensures the security
5
Table 3 Characteristic pressure and temperature values for devices used in the production of CO2 . Nokta
1
2
3
4
5
6
7
8
P (bar) T (◦ C) Nokta P (bar) T (◦ C)
0.1 39 9 19 40
0.35 80 10 19 30
0.30 40 11 18.5 30
0.26 35 12 18.5 10
4.2 90 13 17.5 10
4.2 42 14 17.5 −14
20 95 15 17.5 −25
19 95 16 17.5 −27
of the system by opening when interior pressure reaches to 26 bar and it is closed once the pressure is lowered. The system diagram is provided in Fig. 3. Temperature and Pressure shifts in every step at an site producing CO2 from geothermal energy, from the compression of the raw gas in the blower (1) to the storage tank (16) are shown collectively in Fig. 4 and Table 3. 3.2. Dry ice production Liquid carbon dioxide, which is stored in special tanks with ideal storage conditions for dry ice production with a temperature level between −23 and −28 ◦ C and pressure level between 16 and 19 bar, is fed into the dry ice machine as shown in Fig. 5. Liquid carbon dioxide is released downwards from the above of the machine block. The liquid carbon dioxide suddenly takes the form of snow with the effect of decreasing temperature and pressure under the existing atmospheric conditions. At this instance, a certain amount of CO2 takes the gas form and it is taken inside from the above of the machine block and sent back to the coolers to be condensed again. In order to create vibration, a vibrator is placed over the block. The substance in the form of snow which is taken down with the help of the vibrator is accumulated over the apparatus which provides compression and formation. Accumulated snow is compressed and shaped with the help of a hydraulic piston and a gate which is opened and closed with hydraulic pressure. The resultant dry ice is cut into desired dimensions with chrome saw and stored and transported in boxes made of special Styrofoam. Dry Ice machine is shown schematically in Fig. 5. 4. Cost calculation for production of CO2 from geothermal fluid 4.1. Cost of raw gas Annual capacity of CO2 production plant at Kızıldere Geothermal site is 30,000 ton (Mücasiro˘glu, 2008). For production of 1 kg CO2 is 1.176 kg raw gas is required (Karbogas Inc., 2007). Accordingly, for production of 1 t CO2, we need,
Table 4 The amounts of materials and supplies used in production of a ton liguid CO2 and their share in production cost (%). Item no
Consumable type
Amount
Unit price
Totally $/t CO2
% Rate
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Crude gas (m3 ) Electric consumption KMnO4 NaCO3 Sülfatreat Activated alümina Activated carbon Ammonia Oil Water Staff, insurance, service, mess Subtotal Cost in use Totally
735.294 400 kWh 3 kg 2.4 kg 2.4 kg 0.025 kg 0.10 kg 0.33 kg 0.266 lt 2.5 m3 – – Subtotal cost × %20
0.63 $/m3 0.1417 $/kg 1.5$/kg 0.4 $/kg 1.5 $/kg 2.75 $/kg 23.62 $/kg 1.26 $/kg 1.2 $/kg 1.102 $/m3 – –
4.63 56.68 4.50 0.96 3.60 0.069 2.362 0.42 0.32 2.755 63.00 139.23 27.84 167
2.77 33.94 2.69 0.57 2.16 0.04 1.41 0.25 0.19 1.65 37.72 16.61
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Fig. 3. Cooling and heating unit of CO2 storage tank.
mgas = 1000 × 1.176 = 1176 kg raw gas. Density of 1 m3 raw gas: g = 1.6 kg/m3 (Mücasiro˘glu, 2008). Therefore, the required amount of gas is 735 m3 . As 1 m3 raw gas costs 0.63 cents (Karbogas Inc., 2007) the cost of raw gas needed for production of 1 t CO2 is: ma = 4.63 $/t CO2 . In addition to that, other costs of production; electricity consumption, chemicals and wages, insurance, meals and transportation expenses for personnel working in the plant, are shown in As it can be seen in Table 4, energy consumption of the generators used in production has the biggest share in cost of production (33.94%). The calculation are made on the assumption that CO2 is provided from the condenser of the thermal power plant. In case, he power plant does not work or the raw gas coming from power plant is not sufficient, there will be some increase in the cost of production since the production will be made from the gas that will be taken directly from the reservoir.
4.2. Other costs in the operation It is calculated as 20% of total cost. Hence, the production cost of 1 t CO2 is found to be 167 ($/t).
4.3. The expenses mentioned above do not include tax and transportation cost Tax is paid at a rate of 40% over the profit. Transportation cost is calculated by the total length of transportation expressed in km (round trip including the return) by 0.5 (Mücasiro˘glu, 2008). A formula including these two variables shows the sales price as following: P = [2004 + 8D]/
20 K
−8
$/t CO2
(1)
where;P: sales price ($/t CO2 ) D: total length of transportation (including return) (km)K: Coefficient that also include profitability ratio 5. Results and conclusions In thermal power plants, like Kızıldere, which operate by using geothermal fluids containing to a great extent (1.5–2.5% of total weight) non-condensable CO2 , if the non-condensable gases are not removed from the condenser, they results in an important problem that effect power production negatively. The performance of the steam turbine is dependent on the back pressure at the turbine outlet. Partial pressure of CO2 is calculated as 0.3 bar for Kızıldere power plant. At Kızıldere geothermal power
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Fig. 4. Pressure and temperature values at characteristic points for devices used in the production of CO2 .
Fig. 5. Schematic presentation of dry ice production machine.
plant, the power increase stemming from the expansion of CO2 in the turbine is around 5%, while loss in power production due to partial pressure is 13%. In addition to, 773 kW energy is used for compressor. As a result, the total loss in energy production because of CO2 is around 12%.
Instead of throwing the gas out into the atmosphere by using compressor, it is send to the CO2 production unit, located in the power plant area, where liquid CO2 and dry ice are produced as industrial products. According to the findings of the study:
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1) The production cost of 1 t CO2 by using raw gas obtained from the condenser of the thermal power plant at Kızıldere geothermal area is calculated as $ 167; 2) The cost of production of the same amount of CO2 with other alternative methods varies between $ 190–200; 3) The production of CO2 from geothermal fluid is 13–20% cheaper compared to other methods; 4) The personnel expenses has the biggest share in total cost of production (37.7%) and it is followed by electricity expense (34%) (Table 3); 5) The sales price for 1 t CO2 (P) is determined as following:
P = [2004 + 8D]/
20 K
−8
$/t CO2
(where K: coefficient including profitability ratio; D: total transportation including return) 6) The cost of CO2 corresponds to the 1% of total cost in beverage production and 0.5% of the total cost in gas metal arc welding.
Acknowledgements We would like to thank the Repuclic of Turkey Ministry of Energy and Natural Resources, Karbogas Company and Pamukkale University Institute of Science for supporting this work. References Barit Mining Turk Corporation Limited, 2008. Available from: http://www. baritmaden.com/karbondioxitco2. Bozan, B., 2000. Available from: http://home.anadolu.edu.tr/∼bozan/KIMTEK.htm. Cansever, I˙ ., Gülden, S., 2001. Geotermal Energy. SDÜ Environment Engineering Department. Ekren, O., 2006. Cleaning with dry ice Application, The World of Cooling, vol. 34, 35–42. Karbogas Inc, 2007. Dry Ice Production Process, 1–10. Mücasiro˘glu, F., 2008. Dry Ice Production from Geotermal Energy, Unpublished M.Sc Thesies. Pamukkale University, Institute of Sciences, Denizli, Turkey. Satman, A., Sarak, H., Onur, M., Korkmaz, E.D., 2005. Modeling of production/reinjection behavior of the Kizildere Geothermal Field by a 2-layer geothermal reservoir lumped parameter model. In: Proceedings of the World Geothermal Congress 2005, Antalya, Turkey, 24–29 April. Serpen, U., Türkmen, N., 2007. 23rd annual performance evaluation of kizildere geothermal power plant TESKON. In: Geotermal Energy Conference, I˙ stanbul, pp. 219–228.