Dr. Mathew Aneke Dr. Meihong Wang. 10 th European Conference on Coal Research and Its Application

Transcription

1 Study of Integration of Cryogenic Air Energy Storage and Coal Oxy-fuel Combustion through Modelling and Simulation Dr. Mathew Aneke Dr. Meihong Wang 10 th European Conference on Coal Research and Its Application

2 Presentation Outline Background Process Modelling and Simulation Results and Analysis Conclusions Future Work References 2

3 Background Energy Storage This can be defined as the process of storing energy in any form for later use Why is it necessary? Energy storage allows for the balance of energy supply and demand (Radcliffe, 2013) Improves Energy Efficiency (DOE, 2013) Reduce Energy Wastage Reduce carbon dioxide emission and the associated global warming 3

4 Background How do we store energy? There are different kinds of energy storage strategies. They include (Radcliffe, 2013): Mechanical Storage Pumped Storage Compressed Air Flywheel 4

5 Background Electrochemical Storage Batteries Chemical Storage Hydrogen Electromagnetic Storage Superconductors Thermal Storage Heat Cold Energy Storage (CES) 5

6 Background Amongst the aforementioned energy storage technologies, CES has a lot of potentials due to the following: 6 It is based on already matured process and unit operations Liquefaction of air reduces the volume which makes it easier to store It provides a long term technology for the storage of electricity and can be implemented in commercial scale Its efficiency is relatively high with room for improvement It has potential to be integrated into other clean energy processes like the carbon capture, renewable energy (solar and wind energy)

7 Background Cryogenic Air Energy Storage Potentials Where do we apply CES? Renewable Energy (Solar and Wind) Solar and Wind energy sources occurs intermittently, and because the energy demand varies during peak and off peak periods, there is need to store the excess energy to meet the peak energy demand Carbon Capture & Storage CES has great potential to be integrated in Oxy-fuel combustion Coal Fired Power Plants for Carbon Capture and Storage 7

8 Background: CES Application in Oxy-fuel Combustion Coal Fired Power Plant Oxy-fuel Combustion Coal fired Power Plant An oxy-fuel combustion coal fired power plant is a power plant where coal is combusted in an environment rich in oxygen instead of air. 8

9 Background: CES Application in Oxy-fuel Combustion Coal Fired Power Plant Combustion of coal with only oxygen gives rise to a flue gas rich in CO 2 which can easily be captured and stored The oxygen is obtained through the fractional distillation of air in an Air Separation Unit (ASU) The Nitrogen released from the ASU can be liquefied and used as a cryogenic liquid for cryogenic energy storage (CES). This gives rise to an Integrated Cryogenic Energy Storage and Oxy-Fuel Combustion Coal Fired Power plant 9

10 Process Modelling & Simulation An Integrated CES and Coal Oxy-fuel combustion system comprises 3 different processes linked together. They include: Air Separation Unit (ASU) Liquefaction Process Cryogenic Energy Storage Process These 3 process are modelled and integrated to form the entire CES and Coal Oxy-fuel combustion system as follows: 10

11 Process Modelling & Simulation: Air Separation Unit & Liquefaction System The Models for the Air Separation Unit and liquefaction system were adopted from the work of Casana (2009) and Dubar et al., (1998). The PFD for the model is shown in Figure 2: Brief Process Description In the process, ambient air is first compressed to 4 bar and cooled to o C. The cooled air enters the ASU where the oxygen is removed and used for oxy-fuel combustion process. The Nitrogen rich stream is further cooled to about -188 o C to get liquid Nitrogen which is stored in the tank. 11

12 Air Separation Unit & Liquefaction Process ASU Liquefaction Process 12 Figure 2: Aspen Model of ASU and Liquefaction Process

13 Process Modelling & Simulation: Oxy-fuel Combustion and CO 2 Capture Process The Models for the Oxy-fuel combustion and CO 2 capture were adapted from the work of Casana (2009). The PFD for the model is shown in Figure 3: Brief Process Description In the process, the oxygen from the ASU is combusted with coal to generate a flue gas which is used to produce steam at a pressure of 75 bar and temperature of 773 o C. The steam is used to drive the steam turbine to generate electricity. The steam leaves the turbine at 0.07 bar and 42 o C. The flue gas is recycled back into the boiler to improve the energy efficiency 13

14 Oxy-fuel Combustion and CO 2 Capture Process Figure 3: Aspen Model of Oxy-fuel combustion and CO 2 Capture 14

15 Process Modelling & Simulation: Cryogenic Energy Storage (CES) Process The Model for the CES process was adapted from the work of Chen et al., (2009b). The PFD for the model is shown in Figure 4: Brief Process Description In the process, the liquid Nitrogen (at -188 o C) contained in the tank in the liquefaction process is pumped to 200 bar (-187 o C) through a heat exchanger system in order increase the temperature to 127 o C using waste heat thus turning the liquid Nitrogen into vapour. The Nitrogen vapour is expanded in the turbine to generate electricity. 15

16 Cryogenic Energy Storage Process Figure 4: Aspen Plus Model Cryogenic Energy Storage Process 16

17 rocess Modelling & imulation: Efficiency efinitions Round trip efficiencies Integrated (Overall) Process Total Generator Power Discharge auxilliary ASU Power μ RT = Fuel Input + Charging Power Standalone Oxy fuel Power Plant Oxy fuel Power Discharge auxilliary ASU Power μ OF = Fuel Input Standalone Liquid Nitrogen Power Plant Alone Liquid Nitrogen Power Discharge auxilliary ASU Power μ LA = Charging Power 17 NB: Total Generator Power = Oxy fuel Power + Liquid Nitrogen Power

18 Process Modelling & Simulation: Modelling Parameters & Results Coal The composition of the coal is as shown in Table 1 Table 1: Coal Composition Moisture (wt%) Ultimate (wt%) dry Proximate (wt%) dry Carbon Ash Hydrogen 5.20 Volatile matter Nitrogen 2.00 Fixed carbon Sulphur 0.33 Oxygen

19 Simulation Results Physical Meaning/Units Value Coal (Feedstock) LHV (MWth) O2 produced kg/s Oxy fuel Gross power output (MWe) 737 CO2 compression & auxiliary power consumption (MWe) ASU Power(MWe) 87 Liquid Nitrogen Power Output (MWe) 215 Liquid Nitrogen Discharge Pump power (MWe) 21 Gaseous Nitrogen compression power (MWe) 244 Cryogenic Refrigeration Power (MWe) 19 Round trip efficiency (%)

20 Analyses & Discussions From this modelling work, it can be seen that the integration of CES and Oxy-fuel combustion is a technically viable process with an inherent synergistic advantage The ASU generates oxygen and nitrogen The oxygen is used in the oxy-fuel combustion power plant The nitrogen is further liquefied using electricity during off peak time for cold energy storage 20 The liquid cold nitrogen is further expanded during peak period for power generation.

21 Conclusions Integration of CES and oxy-coal power plant with CO 2 capture has great potential in reducing the carbon footprint of coal fired power plants, improving the overall roundtrip efficiency of the carbon capture process, reducing the energy required in cleaning the flue gas 21 as well as provide a better way for storing electricity during off peak period

22 Future Work Although the various efficiencies reported in this work is within the range of efficiencies reported in the literature, however, future work is needed in this paper to optimize the heat integration of the entire process in order to improve the efficiencies further. 22

23 References A.M. Casana, 2009, Study of Oxy-fuel power plant with CO 2 capture, MSc Dissertation, Cranfield University, UK. C. Dubar, T. Forcey, V. Humphreys, H. Schmidt, 1998, A competitive offshore LNG scheme utilising a gravity base structure and improved nitrogen cycles, In: Proceedings of the LNG 12, Institute of Gas Technology, Perth, WA, Australia, May 4 7. DOE US Department of Energy, (2013), Grid Energy Storage 23 EPA US Environment Protection Agency, (2011) Methodology for Thermal Efficiency and Energy Input Calculations and Analysis of Biomass Cogeneration Unit Characteristics, EPA Docket number: EPA-HQ-OAR April 2007.

24 References H. Chen, Y. Ding, T. Peters, F. Berger, 2009b, Energy Storage and Generation, US Patent 2009/ A1 J. Radcliffe, 2013, Energy Storage Technologies, Ingenia, Issue 54, March,

25 25 THANK YOU