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A high-efficient centrifugal heat pump with industrial waste heat recovery for district heating
Accepted Manuscript A High-Efficient Centrifugal Heat Pump with Industrial Waste Heat Recovery for District Heating Bin Hu, Hua Liu, R.Z. Wang, Hongbo Li, Zhiping Zhang, Sheng Wang PII: DOI: Reference:
S1359-4311(16)32312-2 http://dx.doi.org/10.1016/j.applthermaleng.2017.07.030 ATE 10697
To appear in:
Applied Thermal Engineering
Received Date: Revised Date: Accepted Date:
12 October 2016 2 June 2017 4 July 2017
Please cite this article as: B. Hu, H. Liu, R.Z. Wang, H. Li, Z. Zhang, S. Wang, A High-Efficient Centrifugal Heat Pump with Industrial Waste Heat Recovery for District Heating, Applied Thermal Engineering (2017), doi: http:// dx.doi.org/10.1016/j.applthermaleng.2017.07.030
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A High-Efficient Centrifugal Heat Pump with Industrial Waste Heat Recovery for District Heating Bin Hu1, Hua Liu2, R.Z. Wang1,*, Hongbo Li2, Zhiping Zhang2, Sheng Wang2 1
Institute of Refrigeration and Cryogenics, Shanghai Jiao Tong University Shanghai 200240, China
2
SKL of Air-Conditioning Equipment and System Energy Conservation, GREE Electric Appliances, INC. Zhuhai 519070, China *
Corresponding author, Email: [email protected]; Tel: 86-21-34206548
Abstract: The urban construction area and heating energy consumption in northern China have been increasing greatly in recent years. At the same time, a large amount of low-grade industrial waste heat is released directly to the environment in most industrial plants. To meet the district heating demands and recover the industrial waste heat simultaneously, high-efficiency centrifugal heat pumps are applied for district heating and heat recovery. A permanent-magnetic synchronous frequency-convertible (PSF) centrifugal heat pump is developed which has a much higher COP in comparison with that of conventional heat pumps. In a district heating project with waste heat recovery from industry, testing results have shown that COP of a 500RT PSF centrifugal heat pump could reach 7.1, and the total system COP of the district heating system reaches 4.8. The operating cost for one heating season is just 40.3% of gas-fired boiler heating system. The emission of Carbon Dioxide is reduced by 60.6% and 56.3% when compared with coal-fired boiler and gas-fired boiler heating system, respectively. This shows that application of PSF centrifugal heat pumps to recover the low-grade industrial waste heat for district heating are quite attractive in the north of China cities. Keywords: Permanent-magnetic synchronous, Frequency-convertible, Centrifugal heat pump, District heating, Industrial waste heat
1 Introduction As for 2013, the urban construction area in northern China has accumulated 10.2 billion square meters. Power consumption of heating in northern china reached 166 million tons of standard coal, accounting for 24% of total building energy consumption [1]. With further development of urbanization, the urban construction area of the north of China is expected to reach 15 billion square meters of 2020. The building heating supply demand will further increase. As a result, the construction heating in northern China has a significant potential in building energy-saving field due to high energy consumption and correspondingly huge market. At the same time, along with rapid growth of energy demand for construction heating, traditional heating supply method of coal-fired boiler has brought serious pollution problems. For example, most area of the north of China suffers from heavy haze in winter. Studies [2] have shown that PM2.5 is the main pollution composition of severe haze weather and reduction of NOx emissions is a key to control PM2.5. However the main source of NOx is the burning of fossil fuels (including coal and natural gas). Based on the analysis of pollutant emission sources of haze pollution in Beijing, emissions of coal-fired heating contribute 18.7% of total pollutants [3]. The main reason for the
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haze in northeast China is the exhaust gas of coal-fried and gas-fired boiler from city resident and surrounding houses [4]. In 2013, “Action Plan of Air Pollution Prevention and Control” was issued by the State Council of China. According to the requirements, it is urgent to develop district heating and alternative clean energy and small industrial coal-fired boilers will be fully eliminated [5]. Therefore, sustainable and stable development lies in seeking more efficient and cleaner heating energy, fully replacing the traditional boiler heating method and achieving the goal of energy saving, emission reduction and environment protection. Among all the existing heating sources, coal-fired and gas-fired boilers account for a quite large proportion. The heating area of coal-fired boilers and gas-fired boilers are 4 billion and 0.5 billion square meters [6]. With regard to thermodynamics, combustion temperature of coal-fired and gas-fired boiler is higher than 1000 , then after exchanging heat with several processes, hot water supplied for building heating is about 100
or less. The energy
and exergy loss is larger than most of the heating method [7]. Large amounts of low grade heat could be utilized to meet the requirements of heating and living. Those low grade heat sources include: 1. Waste heat emitted from industrials. The energy efficiency of industrial production process is about 20%-60%, and the rest energy release to the surrounding with the temperature of 30-160 . It is estimated that there is about 9.8×1015 kJ annual industrial waste heat in northern China. 2. Reclaimed water from waste water treatment plants. Water treatment plant has discharged a lot of reclaimed water, whose temperature is around 20 . 3. Geothermal water. Ground water with temperature between 10 and 15
distribute in the most parts of a city. 4. Surface water such as lakes, rivers and sea
water, which has the temperature of 10 . Utilizing more efficiency technologies could provide considerable energy saving in urban heating and reduce the global CO2 emissions by upgrading low temperature heat to higher temperatures. Wu et al. [8] developed a capacityregulated heat pump system to recover waste heat in dyeing industry using a twin-screw compressor. The heat pump system reliably operated to heat the dyeing liquid temperature up to 95°C with an average system COP of 4.2 during the entire heating process. He et al. [9] built a high-temperature heat pump to replace the traditional oil-fired heater for crude oil heating. The field test results showed the overall system COP ranges from 3.5 to 4.4 with an average value of 3.8 and the energy consumed by the heat pump unit is just 57% of that consumed by the oil-fired boiler heater. Wang et al. [10] outlined the possible application of a large scale absorption air-conditioning system by using the low grade geothermal heat source. The economic analysis based on the real-time cooling load profile and the system operation scheme demonstrated the viability of geothermal absorption air-conditioning system. Fang et al. [11] conducted an absorption heat pump district heating project in northern china with 122MW waste heat recovered from a cement plant and a copper smelter. The case analysis showed the thermal energy efficiency of the cement plant increased from 62.9% to 74.3%, and that of copper plant increased from30.1% to 74.7% in heating seasons. R. Lazzarin and M. Noro [12] analyzed the economic performance of gas derived heat pump for district heating during three years of operation. Results demonstrated that current plant layout (heat pump coupled with internal combustion engine) had better energy efficiency than the cogeneration system in district heating. Carli et al. [13] presented the energetic and economic aspects of a district heating and cooling based on a closed-loop ground source heat pump, including the density of population in the district where the buildings are located. Economic
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analysis and payback times are investigated as a function of inhabitant density, adopted solutions, as well as different economic benefit scenarios. Conclusions indicated that primary energy consumption may be reduced by 50-80% compared with traditional systems. Haiwen et al. [14] conducted a field measurement on energy efficiency of a real seawater source heat pump system for district heating. Results showed that there was about an average of 24.2% energy efficiency enhancement potential of the heat pump units in the project. Water-source heat pump systems, considered as a viable alternative to conventional cooling and heating systems, had attractive performance characteristics when properly designed and installed. They offered many performance advantages over air-source heat pumps due to the outstanding heat transfer properties of water and much more favorable temperatures of river or lake water [15]. Nagota et al. [16] examined energy efficiency of a district heating and cooling system by a simulation model with parameters derived from the measurement data. Simulation results for water source heat pump plant revealed that the district heating and cooling system exhibits an energy-saving effect of 22% for heating when compared with individual air source heat pump system. Lund and Persson [17] investigated the potential heat sources of heat pumps for district heating in Denmark. The analysis showed that low-temperature industrial excess heat was potential heat sources at present and that sea water would play a substantial role as a heat source in future energy systems mostly. Although various source heat pump systems have been investigated, there is still lack of large capacity centrifugal heat pump system with industrial waste heat recovered for district heating. Not to mention the Permanent-magnetic Synchronous Frequency-convertible (PSF) centrifugal heat pumps. The system performance and heat recovery efficiency for industrial heat pump can be further improved. In this paper, a PSF centrifugal heat pump system for district heating project is investigated for the thermal performance, economic analysis and environmental protection effect. The operation cost and CO2 reduction of PSF centrifugal heat pump system is compared with that of coalfired and gas-fired boiler. PSF centrifugal heat pump with low grade heat recovery for district heating can greatly reduce local pollutant emissions and increase the thermal efficiency of primary energy, which is a reasonable alternative to coal-fired and gas-fired boiler heating method.
2 PSF centrifugal heat pump The PSF centrifugal heat pump employs several key technologies to improve system efficiency. Such as the twostage compression with vapor injection cycle, compressor pneumatic of all operating condition, two-stage impeller directly driven by high-speed motor, high-speed PSF motor, four-quadrant controlled rectifier. Cycle efficiency, adiabatic efficiency, mechanical efficiency, motor efficiency and inverter efficiency have been improved obviously. The key technologies adopted by the PSF centrifugal heat pump are briefly introduced as follow: 1.
The two-stage compression with vapor injection cycle: In Comparison with single-stage compression heat pump cycle, two-stage compression with vapor injection can increase the system performance by 8%.
2.
Compressor pneumatic of all operating conditions: The traditional centrifugal compressor is designed and manufactured according to the standard operating condition. The PSF centrifugal compressor is designed according to 75% part-load condition, and then expanded to 50% part-load condition and the full-load operating
3
condition. There are also some special designs for centrifugal compressor, such as full length blade closed impeller, centrifugal fan diffuser with low consistency, 360° annular refrigerant injection port. For operation condition between 20% part-load and full-load condition, adiabatic efficiency of compressor is above 85%. 3.
Two-stage impeller directly driven by high-speed motor: The speed-increasing gear (as shown in Figure 1(a)) is removed and replaced by the same shaft drive (as shown in Figure 1(b)). Mechanical loss of centrifugal compressor decreases greatly. If traditional frequency-convertible centrifugal heat pump is compared, mechanical loss reduces 25% for PSF centrifugal heat pump. For example, the mechanical loss of 500RT PSF centrifugal compressor decreases 10kW on the full-load operating condition.
4.
High-speed PSF motor: This kind of motor has the obvious advantage of high speed and large power. The motor efficiency is over 96% and the highest value can reach 97.5% when it is operated for all operating conditions. Compared with traditional frequency-convertible centrifugal heat pump, the motor efficiency increases by more than 3%.
5.
Four-quadrant controlled rectifier: The power factor of frequency converter reaches 0.998, which lead to a current decrease of 10%. The efficiency of frequency converter is up to 97% under the same power consumption condition. The total harmonic distortion of frequency converter is less than 5% with full-loaded condition and there is no need to install auxiliary reactance and harmonic isolator.
(a) Traditional frequency-convertible compressor
(b) Permanent-magnetic synchronous frequency-convertible centrifugal compressor Fig. 1 Structure comparison of traditional frequency-convertible compressor and PSF centrifugal compressor Table 1 Comparison of traditional frequency-convertible and PSF centrifugal heat pump
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Temperature of inlet water in the condenser/
Temperature of outlet water in the condenser/
35.0 40.0
Traditional single-stage frequency-convertible
Permanent-magnetic Synchronous Frequencyconvertible Heating Input Heating capacity power COP /kW /kW
Heating capacity /kW
Input power /kW
Heating COP
45.0
1740.2
347.3
5.0
1759.5
292.8
6.0
50.0
1589.6
361.1
4.4
1612.3
298.5
5.4
Considering key technologies above, as for 500RT PSF heat pump units, when temperatures of the inlet and outlet water in the evaporator are 15 and 10 are 35 and 45
respectively and temperatures of the inlet and outlet water in the condenser
respectively, COP can reach 6.0. And when the temperatures of the inlet and outlet water in the
condenser side are 40 and 50
respectively, COP can reach 5.4. The PSF centrifugal heat pump has much better
performances in comparison with the traditional single-stage frequency-convertible centrifugal heat pump. Table 1 shows the comparison between two products with a capacity about 500RT.
3 Field test evaluation 3.1 PSF centrifugal heat pump design specifications The system is mainly comprised of a PSF centrifugal compressor, a shell and tube condenser, a plate heat exchanger, a main electronic expansion valve, a shell and tube evaporator, a sub expansion value and water pumps. Table 2 summarizes the components of the PSF centrifugal heat pump system along with the major specifications. Table 2 Design specifications of major components of PSF centrifugal heat pump
Components
Design specifications
compressor
Centrifugal compressor; Volume flow rate: 1630 m³·h-1; Nominal rotational speed: 11000 rpm.
Condenser
Shell and tube; shell-side(R134a) ; shell diameter: Φ700 mm; tube-side (water):copper; tube diameter: Φ19.05 mm; tube number: 400; tube length: 3.5 m.
Evaporator
Shell and tube; shell-side(R134a) ; shell diameter: Φ850 mm; tube-side (water):copper; tube diameter: Φ19.05 mm; tube number: 320; tube length: 3.5 m.
Plate heat exchanger
Plate type; heat exchange area: 448 m2; nominal heat capacity: 1600 kW.
Main expansion valve
Effective flow area: 8.5e-4 m2.
Sub Expansion valve
Effective flow area: 2.5e-4 m2.
Water pump
Motor capacity: 37.5 kW, volume flow rate: 150 m³·h-1
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3.2 Field test description The PSF centrifugal heat pumps are used in the north of China for district heating. There are a lot of industrial waste heat sources, e.g. chemical industry waste, oil refinery waste water and chemical fertilizer waste source. In order to evaluate the operating performance of the designed PSF centrifugal heat pumps, a field test is conducted in Lijingwan community, Shijiazhuang City, Hebei Province. According to the building project planning, total heating demand of waste recovery heat pump project is up to 790.5MW, which can satisfy the heating supply for civil buildings in more than 20 million square meters. Then the actual system performance, economic analysis and environment protection of PSF centrifugal heat pump is validated to recycle low grade heat source for heating.
Fig.2 Field test site of district heating projects using PSF centrifugal heat pumps. The building area of the tested project is 80000 square meters, and floor radiation heating is used in winter, which is expected to supply and return water temperature as 45 and 35 , respectively. The heat sink of floor heating is provided by two 500RT PSF centrifugal heat pump units, and both models are LSBLX1800SVP. The heat source is supplied by industrial waste heat with temperature of 25 . Field test site and water system of district heating system are shown in Fig. 2 and 3, respectively.
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Fig.3 Water system of district heating projects
3.3 Testing instruments According to the testing result of Air Conditioning Equipment Quality Supervision and Inspection Center, the actual performance of PSF centrifugal heat pump system is analyzed. The measurement instruments used in the testing process are shown in the Table 3. Table 3 Measurement device and accuracy
Number
Measurement device and model
Range
Accuracy
1
Ultrasonic flow meter (FLCS1012)
Φ25~Φ500
±1.5% of reading
2
Pt100 thermal resistance (ET300)
0~100
±0.2
3
Pressure gauge (CWY-2B)
0-1.6Mpa
±2‰ of reading
4
Clamp power meter (PROVA6600)
0~2000A 15~600V
±2% of reading
5
Power analyzer (HIOKI 3169-20/21)
0~2000A
±0.5% of reading ±0.11%F.S
-40 ~＋85 0~100%RH
±0.3 ±5%RH
-20 ~＋60 0~90%RH
±0.3 ±2%RH
6 7
Temperature and humidity measuring meter (RHLOG-T-H) Hygrothermograph (HM34)
7
4 Results and discussion Based on test facilities and measurement device, field evaluation was conducted to investigate the actual system performance, economic analysis and environment protection of PSF centrifugal heat pumps. The field test was conducted from November 5th of 2013 to March 15th of 2014 for the whole heating season. Testing results are discussed as follows.
4.1 System performance The typical field measurement was from 13:10 February 16th to 13:10 February 17th of 2014. The outdoor average temperature is 1.6 , the maximum is 6.2
and the minimum is -1.7
during test period. When the performance of
heat pumps units and system in Lijingwan District were testing, the indoor temperature of several typical rooms were also collected and recorded. The testing results of average indoor temperature are shown in Fig. 4. It can be seen that the average indoor temperatures of typical rooms in different heating area have met the design and standard requirements [18].
Fig.4 Testing results of indoor average temperature for different rooms The operating performance and energy efficiencies of the PSF centrifugal heat pump unit and the whole system are calculated based on the measurement data. Although the outdoor air temperature during the field measurement period was low, the PSF centrifugal heat pump unit and the whole system were still in operation. As both the heat pump units were in the same capacity and operated stably, one of the heat pump unit was selected as the representative unit and its operational data was collected. The average hot water supply and return temperatures were 45.1 and 16.1
and 35.6
respectively, and the average inlet and outlet temperatures in the evaporator side were 23.7
respectively, which are shown as Fig.5.
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The centrifugal heat pump system was separately tested first to get the actual energy performance of PSF centrifugal heat pump unit. For 500RT PSF centrifugal heat pump unit, the field tested average heating capacity and power consumption of 1# centrifugal heat pump unit is 1714.9 kW and 247 kW, respectively, which is shown in Fig. 6.
Fig.5 Tested temperature profiles of 1# heat pump unit
Fig.6 Tested heating capacity and power consumption profiles of 1# centrifugal heat pump unit
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In order to obtain the actual energy efficiency of the PSF centrifugal heat pump unit, flow rates of heating and cooling water on the condenser and evaporator side were measured by an ultrasonic flow meter, and the power consumption of the PSF centrifugal heat pump unit was acquired by the power analyzer. According to the national standard “water source heat pump unit” [19], coefficient of heating performance of a heat pump unit (i.e. COP) is defined as the ratio of the heating capacity to the power consumption of the heat pump unit. That is:
COP = Qh
Wc
(1)
In which, Qh is the heating capacity of the PSF centrifugal heat pump unit, kW; Wc is the input power of the PSF centrifugal heat pump unit, kW. So the actual COP profile of the 1# centrifugal heat pump unit during measurement period is shown in Fig. 7. The results showed that the COP values of the PSF centrifugal heat pump unit were relatively stable and fluctuated around 6.95 within the range of 6% (i.e. COP = 6.95 ± 0.25).
Fig.7 Tested COP profiles of 1# centrifugal heat pump unit The energy efficiency of the PSF centrifugal heat pump district heating system is the ratio of total heat supply to the overall input power of the system. It can be expressed as:
COPs =
Qh
(Wc + W p )
(2)
In which, COPs is the energy efficiency of the PSF centrifugal heat pump district heating system; Qh is the total heat supply of the system, kW; Ws the total input power of the PSF centrifugal heat pump units, kW; Wp is the total input power of all water pumps in the district heating system, kW. The pumps include water pumps in heat source side and water pumps in customer side of this project. During 24 hours from13:30 February 17th to 13:30 February 18th
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of 2014, the overall system performance were tested and measured. It is concluded from Table 4 that COP of the overall heat pump system is up to 4.8. Table 4 Test results of the actual performance of centrifugal heat pump system
Test items
Test results
Total heat capacity of system(kWh)
58552.6
Total power consumption of system(kWh)
12143.0
Power consumption of 1# heat pump(kWh)
4703.8
Power consumption of 2# heat pump(kWh)
4554.4
Power consumption of water pump in heat source side (kWh)
902.4
Power consumption of water pump in customer side(kWh)
1982.4
COPs of overall heat pump system
4.8
Note: Testing time is from13:30 February 17th to 13:30 February 18th of 2014 and both 1# and 2# centrifugal heat pump are working.
4.2 Economic analysis Statistics about the total power consumption and operation cost in the whole heating season were collected and compared, which are shown in Table 5. During the whole heating season (2904hours), the actual measured power consumption was 571,200 and 287,760 kWh for 1# and 2# heat pump unit, respectively. The total power consumption of PSF centrifugal heat pump system was 1149984 kWh and the power consumption per square meter was 14.4 kWh/(m2·a) in the whole heating season. According to the electricity price for different time and application, the operation cost per square meter was 11.0 ¥/(m2·a). If the traditional single-stage frequencyconvertible centrifugal heat pump was used to supply heat in the same amount, its calculated operating cost was 12.7 ¥/(m2·a). Compared with traditional single-stage frequency-convertible centrifugal heat pump, PSF centrifugal heat pump can save the operating cost by 15.4%. Table 5 Total power consumption and operation cost in the whole heating season
PSF heat pump
Traditional heat pump
Power consumption of 1# heat pump unit(kWh)
571200
700931
Power consumption of 2# heat pump unit(kWh)
287760
353116
Power consumption of water pump(kWh)
291020
291020
1149984
1345068
14.4
16.8
11.0
12.7
Test items
Total power consumption(kWh) 2
Power consumption per square meter in heating season(kWh/m ) 2
Operation cost per square meter in heating season(¥/m )
Note: 1# centrifugal heat pump unit is domestic load, electricity cost is 0.53 ¥/kWh and the electricity cost of other equipment is 1.00 ¥/kWh.
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For more comparisons, the operation cost of gas-fired boiler was analyzed in table 6. The combustion efficiency of gas was supposed as 90% for the whole heating season. With a price of 2.9 ¥/m3 for gas and 1.0 ¥/kWh for water pump, the operating cost was calculated as 27.3 ¥/(m2·a). That is to say PSF centrifugal heat pump system could save relatively 59.7% of the operation cost based on gas-fired boiler heating project. Table 6 Operation cost of gas-fired boiler project
Items
gas-fired boiler
Building energy consumption(GJ/m2·a)
0.30[6]
Nature gas calorific value(MJ/m3)
38.93[6]
Combustion efficiency(%)
90
Heat loss of pipe(%)
10
Consumption of gas(m3/m2·a)
8.56
3
Gas price(¥/m )
2.9 2
Power consumption of water pump(kWh/m )
2.5
Price of electricity(¥/kWh)
1.0
2
Total operating cost(¥/m )
27.3
4.3 Environmental protection By converting the power consumption into the consumption of standard coal in this project, the comparison on primary energy consumption and pollutant emissions of each heating system are shown in Table 7. The standard coal consumption of PSF centrifugal heat hump with industrial waste heat recovery is lower 14.5%, 62.6% and 66.3% than traditional single-stage frequency-convertible centrifugal heat pump, coal-fired boiler and gas-fired boiler, respectively. At the same time, the emissions of Carbon Dioxide, Sulfur Dioxide and Nitrogen Oxide have the same percentage reduction. Ever for single-stage frequency-convertible centrifugal heat pump, the reduction of primary energy consumption and pollutant emissions are promising. For example, emission of Carbon Dioxide is reduced by 60.6% and 56.3% when compared with coal-fired boiler and gas-fired boiler heating system, respectively. As seen in Fig.8, centrifugal heat pumps with industrial waste heat recovery have a very significant environmental effect on coal-fired boiler and gas-fired boiler heating system. Table 7 Pollutant emissions analysis of PSF heat pump
PSF Heat Pump + industrial waste heat
Traditional heat pump + industrial waste heat
Gas-fired boiler
Coal-fired boiler
Power consumption of heat pump (10,000kWh)
85.9
105.4
-
-
Power consumption of water pump (10,000kWh)
29.1
29.1
29.1
29.1
Nature gas consumption(10,000m3)
-
-
68.5
-
Coal consumption(t)
-
-
-
1025a
12
Consumption of Standard coal(t)
374.9b
438.5
1003.0c
1114.3
Carbon Dioxide emission(t)
974.7
1140.1
2607.2
2897.1
Sulfur Dioxide emission(t)
9.0
10.5
24.1
26.7
Nitrogen Oxide emission(t)
2.6
3.1
7.0
7.8
Note: a. The calorific value of standard coal is 29.27MJ/kg. The combustion efficiency of coal-fired boiler is 80% and the heat loss of pipeline is 20%; b. The coal consumption rate in power generation is 326gce/kWh; c. The conversion factor of nature gas is 1.33kgce/m3; d. Carbon Dioxide, Sulfur Dioxide and Nitrogen Oxide emissions of per standard coal are 2.6t, 24kg and 7kg, relatively.
Fig.8 CO2 emissions analysis for different heating system
5 Conclusions In recent years, the urban heating area and energy consumption grow up rapidly in northern China. Traditional heating methods of coal-fired boiler and gas-fired boiler have lots of problems such as low energy efficiency, heavy pollution and so on. It is urgent to seek for more efficient and clean heating methods. Meanwhile, a large number of low grade industrial waste energy is released in northern China. Heat pump system with low grade industrial waste recovery and heating supply could play a very significant role in meeting the increasing demands for energy conversation and emission reduction. The PSF centrifugal heat pump adopts some key technologies such as two-stage compression with vapor injection cycle, compressor pneumatic of all operating conditions, two-stage impeller directly driven by high-speed motor, high-speed Permanent-magnetic Synchronous Frequency-convertible motor and four-quadrant controlled rectifier.
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The compressor efficiency and heating COP are greatly improved relative to traditional single-stage frequencyconvertible centrifugal heat pump. In the practical application of district heating project, the PSF centrifugal heat pump with low grade industrial waste heat recovery and heating supply has the following advantages: 1. the heating COP of 500 RT centrifugal heat pump unit is up to 7.1 and the total system COP of the centrifugal heat pump DH system reaches 4.8; 2. the operating cost per square meter for one heat season is just 11.0 ¥/(m2·a), which is 40.3% of gas-fired boiler heating system; 3.emissions of Carbon Dioxide, Sulfur Dioxide and Nitrogen Oxide are greatly reduced. For example, emission of Carbon Dioxide is reduced by 60.6% and 56.3% when compared with coal-fired boiler and gas-fired boiler heating system, respectively. As a new high-efficient, energy saving and clean heating method, PSF centrifugal heat pump with industrial waste heat recovery has a promising prospect in district heating application.
Acknowledgements This work was supported by National key research and development program-China “High efficiency compression heat pump with industrial waste heat recovery” (2016YFB0601201).
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[13] Carli M, Galgaro A, Pasqualetto M. Energetic and economic aspects of a heating and cooling district in a mild climate based on closed loop ground source heat pump. Applied Thermal Engineering. 2014, 71:895-904. [14] Haiwen S. Lin DM. Jing S. Field measurement and energy efficiency enhancement potential of a seawater source heat pump district heating system. Energy and Buildings. 2015, 105:352-357. [15] Kavanaugh SP. Design considerations for ground and water source heat pumps in southern climates. ASHRAE Trans. 1989, 95:1139-1149. [16] Nagota T, Shimoda Y, Mizuno M. Verification of the energy-saving effect of the district heating and cooling systemSimulation of an electric-driven heat pump system. Energy and Buildings. 2008, 40:732-741. [17] Lund R, Persson U. Mapping of potential heat sources for heat pumps for district heating in Denmark. Energy. 2016, 110:129-138. [18] Y.Q. Lu, Practical Handbook of Heating and Air-Conditioning Design, 2nd ed. China Building Construction Industry press, Beijing, 2007. [19] China Machinery Industry Federation (GB/T 19409-2004) Water Source Heat Pump Unit, General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China (AQSIQ).
Highlights • • • •
A permanent-magnetic synchronous frequency-convertible centrifugal heat pump was developed. Two-stage impeller directly driven by high-speed motor was adopted in PSF centrifugal heat pump. The heating COP of 500 RT centrifugal heat pump units is up to 7.1. The total system COP of the centrifugal heat pump DH system reaches 4.8.
15
S1359-4311(16)32312-2 http://dx.doi.org/10.1016/j.applthermaleng.2017.07.030 ATE 10697
To appear in:
Applied Thermal Engineering
Received Date: Revised Date: Accepted Date:
12 October 2016 2 June 2017 4 July 2017
Please cite this article as: B. Hu, H. Liu, R.Z. Wang, H. Li, Z. Zhang, S. Wang, A High-Efficient Centrifugal Heat Pump with Industrial Waste Heat Recovery for District Heating, Applied Thermal Engineering (2017), doi: http:// dx.doi.org/10.1016/j.applthermaleng.2017.07.030
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A High-Efficient Centrifugal Heat Pump with Industrial Waste Heat Recovery for District Heating Bin Hu1, Hua Liu2, R.Z. Wang1,*, Hongbo Li2, Zhiping Zhang2, Sheng Wang2 1
Institute of Refrigeration and Cryogenics, Shanghai Jiao Tong University Shanghai 200240, China
2
SKL of Air-Conditioning Equipment and System Energy Conservation, GREE Electric Appliances, INC. Zhuhai 519070, China *
Corresponding author, Email: [email protected]; Tel: 86-21-34206548
Abstract: The urban construction area and heating energy consumption in northern China have been increasing greatly in recent years. At the same time, a large amount of low-grade industrial waste heat is released directly to the environment in most industrial plants. To meet the district heating demands and recover the industrial waste heat simultaneously, high-efficiency centrifugal heat pumps are applied for district heating and heat recovery. A permanent-magnetic synchronous frequency-convertible (PSF) centrifugal heat pump is developed which has a much higher COP in comparison with that of conventional heat pumps. In a district heating project with waste heat recovery from industry, testing results have shown that COP of a 500RT PSF centrifugal heat pump could reach 7.1, and the total system COP of the district heating system reaches 4.8. The operating cost for one heating season is just 40.3% of gas-fired boiler heating system. The emission of Carbon Dioxide is reduced by 60.6% and 56.3% when compared with coal-fired boiler and gas-fired boiler heating system, respectively. This shows that application of PSF centrifugal heat pumps to recover the low-grade industrial waste heat for district heating are quite attractive in the north of China cities. Keywords: Permanent-magnetic synchronous, Frequency-convertible, Centrifugal heat pump, District heating, Industrial waste heat
1 Introduction As for 2013, the urban construction area in northern China has accumulated 10.2 billion square meters. Power consumption of heating in northern china reached 166 million tons of standard coal, accounting for 24% of total building energy consumption [1]. With further development of urbanization, the urban construction area of the north of China is expected to reach 15 billion square meters of 2020. The building heating supply demand will further increase. As a result, the construction heating in northern China has a significant potential in building energy-saving field due to high energy consumption and correspondingly huge market. At the same time, along with rapid growth of energy demand for construction heating, traditional heating supply method of coal-fired boiler has brought serious pollution problems. For example, most area of the north of China suffers from heavy haze in winter. Studies [2] have shown that PM2.5 is the main pollution composition of severe haze weather and reduction of NOx emissions is a key to control PM2.5. However the main source of NOx is the burning of fossil fuels (including coal and natural gas). Based on the analysis of pollutant emission sources of haze pollution in Beijing, emissions of coal-fired heating contribute 18.7% of total pollutants [3]. The main reason for the
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haze in northeast China is the exhaust gas of coal-fried and gas-fired boiler from city resident and surrounding houses [4]. In 2013, “Action Plan of Air Pollution Prevention and Control” was issued by the State Council of China. According to the requirements, it is urgent to develop district heating and alternative clean energy and small industrial coal-fired boilers will be fully eliminated [5]. Therefore, sustainable and stable development lies in seeking more efficient and cleaner heating energy, fully replacing the traditional boiler heating method and achieving the goal of energy saving, emission reduction and environment protection. Among all the existing heating sources, coal-fired and gas-fired boilers account for a quite large proportion. The heating area of coal-fired boilers and gas-fired boilers are 4 billion and 0.5 billion square meters [6]. With regard to thermodynamics, combustion temperature of coal-fired and gas-fired boiler is higher than 1000 , then after exchanging heat with several processes, hot water supplied for building heating is about 100
or less. The energy
and exergy loss is larger than most of the heating method [7]. Large amounts of low grade heat could be utilized to meet the requirements of heating and living. Those low grade heat sources include: 1. Waste heat emitted from industrials. The energy efficiency of industrial production process is about 20%-60%, and the rest energy release to the surrounding with the temperature of 30-160 . It is estimated that there is about 9.8×1015 kJ annual industrial waste heat in northern China. 2. Reclaimed water from waste water treatment plants. Water treatment plant has discharged a lot of reclaimed water, whose temperature is around 20 . 3. Geothermal water. Ground water with temperature between 10 and 15
distribute in the most parts of a city. 4. Surface water such as lakes, rivers and sea
water, which has the temperature of 10 . Utilizing more efficiency technologies could provide considerable energy saving in urban heating and reduce the global CO2 emissions by upgrading low temperature heat to higher temperatures. Wu et al. [8] developed a capacityregulated heat pump system to recover waste heat in dyeing industry using a twin-screw compressor. The heat pump system reliably operated to heat the dyeing liquid temperature up to 95°C with an average system COP of 4.2 during the entire heating process. He et al. [9] built a high-temperature heat pump to replace the traditional oil-fired heater for crude oil heating. The field test results showed the overall system COP ranges from 3.5 to 4.4 with an average value of 3.8 and the energy consumed by the heat pump unit is just 57% of that consumed by the oil-fired boiler heater. Wang et al. [10] outlined the possible application of a large scale absorption air-conditioning system by using the low grade geothermal heat source. The economic analysis based on the real-time cooling load profile and the system operation scheme demonstrated the viability of geothermal absorption air-conditioning system. Fang et al. [11] conducted an absorption heat pump district heating project in northern china with 122MW waste heat recovered from a cement plant and a copper smelter. The case analysis showed the thermal energy efficiency of the cement plant increased from 62.9% to 74.3%, and that of copper plant increased from30.1% to 74.7% in heating seasons. R. Lazzarin and M. Noro [12] analyzed the economic performance of gas derived heat pump for district heating during three years of operation. Results demonstrated that current plant layout (heat pump coupled with internal combustion engine) had better energy efficiency than the cogeneration system in district heating. Carli et al. [13] presented the energetic and economic aspects of a district heating and cooling based on a closed-loop ground source heat pump, including the density of population in the district where the buildings are located. Economic
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analysis and payback times are investigated as a function of inhabitant density, adopted solutions, as well as different economic benefit scenarios. Conclusions indicated that primary energy consumption may be reduced by 50-80% compared with traditional systems. Haiwen et al. [14] conducted a field measurement on energy efficiency of a real seawater source heat pump system for district heating. Results showed that there was about an average of 24.2% energy efficiency enhancement potential of the heat pump units in the project. Water-source heat pump systems, considered as a viable alternative to conventional cooling and heating systems, had attractive performance characteristics when properly designed and installed. They offered many performance advantages over air-source heat pumps due to the outstanding heat transfer properties of water and much more favorable temperatures of river or lake water [15]. Nagota et al. [16] examined energy efficiency of a district heating and cooling system by a simulation model with parameters derived from the measurement data. Simulation results for water source heat pump plant revealed that the district heating and cooling system exhibits an energy-saving effect of 22% for heating when compared with individual air source heat pump system. Lund and Persson [17] investigated the potential heat sources of heat pumps for district heating in Denmark. The analysis showed that low-temperature industrial excess heat was potential heat sources at present and that sea water would play a substantial role as a heat source in future energy systems mostly. Although various source heat pump systems have been investigated, there is still lack of large capacity centrifugal heat pump system with industrial waste heat recovered for district heating. Not to mention the Permanent-magnetic Synchronous Frequency-convertible (PSF) centrifugal heat pumps. The system performance and heat recovery efficiency for industrial heat pump can be further improved. In this paper, a PSF centrifugal heat pump system for district heating project is investigated for the thermal performance, economic analysis and environmental protection effect. The operation cost and CO2 reduction of PSF centrifugal heat pump system is compared with that of coalfired and gas-fired boiler. PSF centrifugal heat pump with low grade heat recovery for district heating can greatly reduce local pollutant emissions and increase the thermal efficiency of primary energy, which is a reasonable alternative to coal-fired and gas-fired boiler heating method.
2 PSF centrifugal heat pump The PSF centrifugal heat pump employs several key technologies to improve system efficiency. Such as the twostage compression with vapor injection cycle, compressor pneumatic of all operating condition, two-stage impeller directly driven by high-speed motor, high-speed PSF motor, four-quadrant controlled rectifier. Cycle efficiency, adiabatic efficiency, mechanical efficiency, motor efficiency and inverter efficiency have been improved obviously. The key technologies adopted by the PSF centrifugal heat pump are briefly introduced as follow: 1.
The two-stage compression with vapor injection cycle: In Comparison with single-stage compression heat pump cycle, two-stage compression with vapor injection can increase the system performance by 8%.
2.
Compressor pneumatic of all operating conditions: The traditional centrifugal compressor is designed and manufactured according to the standard operating condition. The PSF centrifugal compressor is designed according to 75% part-load condition, and then expanded to 50% part-load condition and the full-load operating
3
condition. There are also some special designs for centrifugal compressor, such as full length blade closed impeller, centrifugal fan diffuser with low consistency, 360° annular refrigerant injection port. For operation condition between 20% part-load and full-load condition, adiabatic efficiency of compressor is above 85%. 3.
Two-stage impeller directly driven by high-speed motor: The speed-increasing gear (as shown in Figure 1(a)) is removed and replaced by the same shaft drive (as shown in Figure 1(b)). Mechanical loss of centrifugal compressor decreases greatly. If traditional frequency-convertible centrifugal heat pump is compared, mechanical loss reduces 25% for PSF centrifugal heat pump. For example, the mechanical loss of 500RT PSF centrifugal compressor decreases 10kW on the full-load operating condition.
4.
High-speed PSF motor: This kind of motor has the obvious advantage of high speed and large power. The motor efficiency is over 96% and the highest value can reach 97.5% when it is operated for all operating conditions. Compared with traditional frequency-convertible centrifugal heat pump, the motor efficiency increases by more than 3%.
5.
Four-quadrant controlled rectifier: The power factor of frequency converter reaches 0.998, which lead to a current decrease of 10%. The efficiency of frequency converter is up to 97% under the same power consumption condition. The total harmonic distortion of frequency converter is less than 5% with full-loaded condition and there is no need to install auxiliary reactance and harmonic isolator.
(a) Traditional frequency-convertible compressor
(b) Permanent-magnetic synchronous frequency-convertible centrifugal compressor Fig. 1 Structure comparison of traditional frequency-convertible compressor and PSF centrifugal compressor Table 1 Comparison of traditional frequency-convertible and PSF centrifugal heat pump
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Temperature of inlet water in the condenser/
Temperature of outlet water in the condenser/
35.0 40.0
Traditional single-stage frequency-convertible
Permanent-magnetic Synchronous Frequencyconvertible Heating Input Heating capacity power COP /kW /kW
Heating capacity /kW
Input power /kW
Heating COP
45.0
1740.2
347.3
5.0
1759.5
292.8
6.0
50.0
1589.6
361.1
4.4
1612.3
298.5
5.4
Considering key technologies above, as for 500RT PSF heat pump units, when temperatures of the inlet and outlet water in the evaporator are 15 and 10 are 35 and 45
respectively and temperatures of the inlet and outlet water in the condenser
respectively, COP can reach 6.0. And when the temperatures of the inlet and outlet water in the
condenser side are 40 and 50
respectively, COP can reach 5.4. The PSF centrifugal heat pump has much better
performances in comparison with the traditional single-stage frequency-convertible centrifugal heat pump. Table 1 shows the comparison between two products with a capacity about 500RT.
3 Field test evaluation 3.1 PSF centrifugal heat pump design specifications The system is mainly comprised of a PSF centrifugal compressor, a shell and tube condenser, a plate heat exchanger, a main electronic expansion valve, a shell and tube evaporator, a sub expansion value and water pumps. Table 2 summarizes the components of the PSF centrifugal heat pump system along with the major specifications. Table 2 Design specifications of major components of PSF centrifugal heat pump
Components
Design specifications
compressor
Centrifugal compressor; Volume flow rate: 1630 m³·h-1; Nominal rotational speed: 11000 rpm.
Condenser
Shell and tube; shell-side(R134a) ; shell diameter: Φ700 mm; tube-side (water):copper; tube diameter: Φ19.05 mm; tube number: 400; tube length: 3.5 m.
Evaporator
Shell and tube; shell-side(R134a) ; shell diameter: Φ850 mm; tube-side (water):copper; tube diameter: Φ19.05 mm; tube number: 320; tube length: 3.5 m.
Plate heat exchanger
Plate type; heat exchange area: 448 m2; nominal heat capacity: 1600 kW.
Main expansion valve
Effective flow area: 8.5e-4 m2.
Sub Expansion valve
Effective flow area: 2.5e-4 m2.
Water pump
Motor capacity: 37.5 kW, volume flow rate: 150 m³·h-1
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3.2 Field test description The PSF centrifugal heat pumps are used in the north of China for district heating. There are a lot of industrial waste heat sources, e.g. chemical industry waste, oil refinery waste water and chemical fertilizer waste source. In order to evaluate the operating performance of the designed PSF centrifugal heat pumps, a field test is conducted in Lijingwan community, Shijiazhuang City, Hebei Province. According to the building project planning, total heating demand of waste recovery heat pump project is up to 790.5MW, which can satisfy the heating supply for civil buildings in more than 20 million square meters. Then the actual system performance, economic analysis and environment protection of PSF centrifugal heat pump is validated to recycle low grade heat source for heating.
Fig.2 Field test site of district heating projects using PSF centrifugal heat pumps. The building area of the tested project is 80000 square meters, and floor radiation heating is used in winter, which is expected to supply and return water temperature as 45 and 35 , respectively. The heat sink of floor heating is provided by two 500RT PSF centrifugal heat pump units, and both models are LSBLX1800SVP. The heat source is supplied by industrial waste heat with temperature of 25 . Field test site and water system of district heating system are shown in Fig. 2 and 3, respectively.
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Fig.3 Water system of district heating projects
3.3 Testing instruments According to the testing result of Air Conditioning Equipment Quality Supervision and Inspection Center, the actual performance of PSF centrifugal heat pump system is analyzed. The measurement instruments used in the testing process are shown in the Table 3. Table 3 Measurement device and accuracy
Number
Measurement device and model
Range
Accuracy
1
Ultrasonic flow meter (FLCS1012)
Φ25~Φ500
±1.5% of reading
2
Pt100 thermal resistance (ET300)
0~100
±0.2
3
Pressure gauge (CWY-2B)
0-1.6Mpa
±2‰ of reading
4
Clamp power meter (PROVA6600)
0~2000A 15~600V
±2% of reading
5
Power analyzer (HIOKI 3169-20/21)
0~2000A
±0.5% of reading ±0.11%F.S
-40 ~＋85 0~100%RH
±0.3 ±5%RH
-20 ~＋60 0~90%RH
±0.3 ±2%RH
6 7
Temperature and humidity measuring meter (RHLOG-T-H) Hygrothermograph (HM34)
7
4 Results and discussion Based on test facilities and measurement device, field evaluation was conducted to investigate the actual system performance, economic analysis and environment protection of PSF centrifugal heat pumps. The field test was conducted from November 5th of 2013 to March 15th of 2014 for the whole heating season. Testing results are discussed as follows.
4.1 System performance The typical field measurement was from 13:10 February 16th to 13:10 February 17th of 2014. The outdoor average temperature is 1.6 , the maximum is 6.2
and the minimum is -1.7
during test period. When the performance of
heat pumps units and system in Lijingwan District were testing, the indoor temperature of several typical rooms were also collected and recorded. The testing results of average indoor temperature are shown in Fig. 4. It can be seen that the average indoor temperatures of typical rooms in different heating area have met the design and standard requirements [18].
Fig.4 Testing results of indoor average temperature for different rooms The operating performance and energy efficiencies of the PSF centrifugal heat pump unit and the whole system are calculated based on the measurement data. Although the outdoor air temperature during the field measurement period was low, the PSF centrifugal heat pump unit and the whole system were still in operation. As both the heat pump units were in the same capacity and operated stably, one of the heat pump unit was selected as the representative unit and its operational data was collected. The average hot water supply and return temperatures were 45.1 and 16.1
and 35.6
respectively, and the average inlet and outlet temperatures in the evaporator side were 23.7
respectively, which are shown as Fig.5.
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The centrifugal heat pump system was separately tested first to get the actual energy performance of PSF centrifugal heat pump unit. For 500RT PSF centrifugal heat pump unit, the field tested average heating capacity and power consumption of 1# centrifugal heat pump unit is 1714.9 kW and 247 kW, respectively, which is shown in Fig. 6.
Fig.5 Tested temperature profiles of 1# heat pump unit
Fig.6 Tested heating capacity and power consumption profiles of 1# centrifugal heat pump unit
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In order to obtain the actual energy efficiency of the PSF centrifugal heat pump unit, flow rates of heating and cooling water on the condenser and evaporator side were measured by an ultrasonic flow meter, and the power consumption of the PSF centrifugal heat pump unit was acquired by the power analyzer. According to the national standard “water source heat pump unit” [19], coefficient of heating performance of a heat pump unit (i.e. COP) is defined as the ratio of the heating capacity to the power consumption of the heat pump unit. That is:
COP = Qh
Wc
(1)
In which, Qh is the heating capacity of the PSF centrifugal heat pump unit, kW; Wc is the input power of the PSF centrifugal heat pump unit, kW. So the actual COP profile of the 1# centrifugal heat pump unit during measurement period is shown in Fig. 7. The results showed that the COP values of the PSF centrifugal heat pump unit were relatively stable and fluctuated around 6.95 within the range of 6% (i.e. COP = 6.95 ± 0.25).
Fig.7 Tested COP profiles of 1# centrifugal heat pump unit The energy efficiency of the PSF centrifugal heat pump district heating system is the ratio of total heat supply to the overall input power of the system. It can be expressed as:
COPs =
Qh
(Wc + W p )
(2)
In which, COPs is the energy efficiency of the PSF centrifugal heat pump district heating system; Qh is the total heat supply of the system, kW; Ws the total input power of the PSF centrifugal heat pump units, kW; Wp is the total input power of all water pumps in the district heating system, kW. The pumps include water pumps in heat source side and water pumps in customer side of this project. During 24 hours from13:30 February 17th to 13:30 February 18th
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of 2014, the overall system performance were tested and measured. It is concluded from Table 4 that COP of the overall heat pump system is up to 4.8. Table 4 Test results of the actual performance of centrifugal heat pump system
Test items
Test results
Total heat capacity of system(kWh)
58552.6
Total power consumption of system(kWh)
12143.0
Power consumption of 1# heat pump(kWh)
4703.8
Power consumption of 2# heat pump(kWh)
4554.4
Power consumption of water pump in heat source side (kWh)
902.4
Power consumption of water pump in customer side(kWh)
1982.4
COPs of overall heat pump system
4.8
Note: Testing time is from13:30 February 17th to 13:30 February 18th of 2014 and both 1# and 2# centrifugal heat pump are working.
4.2 Economic analysis Statistics about the total power consumption and operation cost in the whole heating season were collected and compared, which are shown in Table 5. During the whole heating season (2904hours), the actual measured power consumption was 571,200 and 287,760 kWh for 1# and 2# heat pump unit, respectively. The total power consumption of PSF centrifugal heat pump system was 1149984 kWh and the power consumption per square meter was 14.4 kWh/(m2·a) in the whole heating season. According to the electricity price for different time and application, the operation cost per square meter was 11.0 ¥/(m2·a). If the traditional single-stage frequencyconvertible centrifugal heat pump was used to supply heat in the same amount, its calculated operating cost was 12.7 ¥/(m2·a). Compared with traditional single-stage frequency-convertible centrifugal heat pump, PSF centrifugal heat pump can save the operating cost by 15.4%. Table 5 Total power consumption and operation cost in the whole heating season
PSF heat pump
Traditional heat pump
Power consumption of 1# heat pump unit(kWh)
571200
700931
Power consumption of 2# heat pump unit(kWh)
287760
353116
Power consumption of water pump(kWh)
291020
291020
1149984
1345068
14.4
16.8
11.0
12.7
Test items
Total power consumption(kWh) 2
Power consumption per square meter in heating season(kWh/m ) 2
Operation cost per square meter in heating season(¥/m )
Note: 1# centrifugal heat pump unit is domestic load, electricity cost is 0.53 ¥/kWh and the electricity cost of other equipment is 1.00 ¥/kWh.
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For more comparisons, the operation cost of gas-fired boiler was analyzed in table 6. The combustion efficiency of gas was supposed as 90% for the whole heating season. With a price of 2.9 ¥/m3 for gas and 1.0 ¥/kWh for water pump, the operating cost was calculated as 27.3 ¥/(m2·a). That is to say PSF centrifugal heat pump system could save relatively 59.7% of the operation cost based on gas-fired boiler heating project. Table 6 Operation cost of gas-fired boiler project
Items
gas-fired boiler
Building energy consumption(GJ/m2·a)
0.30[6]
Nature gas calorific value(MJ/m3)
38.93[6]
Combustion efficiency(%)
90
Heat loss of pipe(%)
10
Consumption of gas(m3/m2·a)
8.56
3
Gas price(¥/m )
2.9 2
Power consumption of water pump(kWh/m )
2.5
Price of electricity(¥/kWh)
1.0
2
Total operating cost(¥/m )
27.3
4.3 Environmental protection By converting the power consumption into the consumption of standard coal in this project, the comparison on primary energy consumption and pollutant emissions of each heating system are shown in Table 7. The standard coal consumption of PSF centrifugal heat hump with industrial waste heat recovery is lower 14.5%, 62.6% and 66.3% than traditional single-stage frequency-convertible centrifugal heat pump, coal-fired boiler and gas-fired boiler, respectively. At the same time, the emissions of Carbon Dioxide, Sulfur Dioxide and Nitrogen Oxide have the same percentage reduction. Ever for single-stage frequency-convertible centrifugal heat pump, the reduction of primary energy consumption and pollutant emissions are promising. For example, emission of Carbon Dioxide is reduced by 60.6% and 56.3% when compared with coal-fired boiler and gas-fired boiler heating system, respectively. As seen in Fig.8, centrifugal heat pumps with industrial waste heat recovery have a very significant environmental effect on coal-fired boiler and gas-fired boiler heating system. Table 7 Pollutant emissions analysis of PSF heat pump
PSF Heat Pump + industrial waste heat
Traditional heat pump + industrial waste heat
Gas-fired boiler
Coal-fired boiler
Power consumption of heat pump (10,000kWh)
85.9
105.4
-
-
Power consumption of water pump (10,000kWh)
29.1
29.1
29.1
29.1
Nature gas consumption(10,000m3)
-
-
68.5
-
Coal consumption(t)
-
-
-
1025a
12
Consumption of Standard coal(t)
374.9b
438.5
1003.0c
1114.3
Carbon Dioxide emission(t)
974.7
1140.1
2607.2
2897.1
Sulfur Dioxide emission(t)
9.0
10.5
24.1
26.7
Nitrogen Oxide emission(t)
2.6
3.1
7.0
7.8
Note: a. The calorific value of standard coal is 29.27MJ/kg. The combustion efficiency of coal-fired boiler is 80% and the heat loss of pipeline is 20%; b. The coal consumption rate in power generation is 326gce/kWh; c. The conversion factor of nature gas is 1.33kgce/m3; d. Carbon Dioxide, Sulfur Dioxide and Nitrogen Oxide emissions of per standard coal are 2.6t, 24kg and 7kg, relatively.
Fig.8 CO2 emissions analysis for different heating system
5 Conclusions In recent years, the urban heating area and energy consumption grow up rapidly in northern China. Traditional heating methods of coal-fired boiler and gas-fired boiler have lots of problems such as low energy efficiency, heavy pollution and so on. It is urgent to seek for more efficient and clean heating methods. Meanwhile, a large number of low grade industrial waste energy is released in northern China. Heat pump system with low grade industrial waste recovery and heating supply could play a very significant role in meeting the increasing demands for energy conversation and emission reduction. The PSF centrifugal heat pump adopts some key technologies such as two-stage compression with vapor injection cycle, compressor pneumatic of all operating conditions, two-stage impeller directly driven by high-speed motor, high-speed Permanent-magnetic Synchronous Frequency-convertible motor and four-quadrant controlled rectifier.
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The compressor efficiency and heating COP are greatly improved relative to traditional single-stage frequencyconvertible centrifugal heat pump. In the practical application of district heating project, the PSF centrifugal heat pump with low grade industrial waste heat recovery and heating supply has the following advantages: 1. the heating COP of 500 RT centrifugal heat pump unit is up to 7.1 and the total system COP of the centrifugal heat pump DH system reaches 4.8; 2. the operating cost per square meter for one heat season is just 11.0 ¥/(m2·a), which is 40.3% of gas-fired boiler heating system; 3.emissions of Carbon Dioxide, Sulfur Dioxide and Nitrogen Oxide are greatly reduced. For example, emission of Carbon Dioxide is reduced by 60.6% and 56.3% when compared with coal-fired boiler and gas-fired boiler heating system, respectively. As a new high-efficient, energy saving and clean heating method, PSF centrifugal heat pump with industrial waste heat recovery has a promising prospect in district heating application.
Acknowledgements This work was supported by National key research and development program-China “High efficiency compression heat pump with industrial waste heat recovery” (2016YFB0601201).
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Highlights • • • •
A permanent-magnetic synchronous frequency-convertible centrifugal heat pump was developed. Two-stage impeller directly driven by high-speed motor was adopted in PSF centrifugal heat pump. The heating COP of 500 RT centrifugal heat pump units is up to 7.1. The total system COP of the centrifugal heat pump DH system reaches 4.8.
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