Development and Cost Estimation of Green Gas Reduction Process for Power Plant

The systematic and quantitative approach on the environmental pollution is a significant challenge in highly regulated industries, such as power plants, where a large amount of waste gas including greenhouse gas must be discharged. We simulated various CO2 reduction processes and estimated the total cost of those. In this study, an environmental pollution impact is analyzed by the process operating conditions. First, this paper contains the simulation of the CO2 reduction process for three absorbents(MEA (monoethanolamine), M-H amine solution, T-D amine solution) in the same operating condition. The simulation results include CO2 recovery rate and CO2 mole fraction in CO2-rich gas of each absorbent. The T-D solution is inferior to others definitely. While the MEA solution and the M-H solution shows almost perfect CO2 recovery rate, CO2 recovery rate of the T-D solution is only 90%. However, all the operation conditions such as the inner temperature of the reboiler, the pressure of the stripper bottom, the temperature of the feed, the temperature of the absorbent and recycling rate of the absorbent are fitted for the MEA solution. The improved results of other absorbents can be expected as operation conditions are altered. For example, when the reboiler duty is changed 623MJ/h into 600MJ/h, about 2% in CO2 recovery rate of the M-H solution is increased and the energy consumption is decreased simultaneously. Second, cost estimation of the reduction process are performed for three absorbents considering investment cost, operating cost and raw material cost. As a result, the M-H solution is suitable with respect to operating cost and investment cost. The MEA solution seems to be better in accordance with raw material cost. In conclusion, the CO2 recovery rate of the M-H solution is similar to CO2 recovery rate of MEA solution, but total cost for M-H solution is lower than that for MEA solution. Based on this study, it is possible that an environment friendly design and an environment friendly operation can be achieved simultaneously in some parts. KEYWORD CO2 recovery process, Simulation, Cost estimation INTRODUCTION Since the beginning of industrial revolution, the ratio of fossil fuel used has been increased every year. The major energy sources come from coal, natural gas, and petroleum, all of which make air pollution problem. Fossil fuel combustion produces a large amount of CO2. CO2 is also one of causes of the global greenhouse effect. Owing to the emission of combustion gases, excess CO2 accumulates around the atmosphere. The amount of CO2 in the atmosphere increases globally about six billion tones per year. The combustion of fuel for power production is in most cases the largest contributor of greenhouse gas emissions from a process industry (H. Axelsson, 1999). Energy consumption and requirement increase quickly at present, but there is little clean type of energy available to use as a power source. Therefore, it is most important to recover CO2 from the flue gases to avoid excessive CO2 emission. The typical CO2 reduction process does not remove contaminants perfectly but it just transfers those from one medium to another. And the technology leads to the cost required according to the change of social criteria and the strengthening of an emission regulation. Therefore, the introduction of the novel estimation system considering the optimal CO2 emission and cost consumption is required. SIMULATION for CASE STUDY Figure 1 shows PFD of CO2 reduction process to remove CO2 of the waste gas for power plant. The waste gas goes into absorber and it meets absorbent with counter flow in absorber. The CO2-lean gas is discharged into air and CO2-rich solution is pumping into lean/rich-cross heat exchanger. In cross heat exchanger, the CO2-rich solution is heating and the CO2-lean solution is cooling. And then to regenerate solvent (absorbent), CO2-rich solution is heating in the reboiler again and it enters regenerator. In generator, CO2 and vapor go up to the condenser and absorbent is liquefied. Figure 1. PFD of CO2 reduction process Table 1 shows the composition of the waste gas in a coal thermoelectric power plant; the net capacity of target plant is about 250MW. Table 1. Composition of the waste gas in a 250MW power plant Flow rate (mN/s) 683.0 Pressure (kPa) 101.0 N2 72.5 Composition (mol-%) CO2 6.9 H2O 15.2 O2 5.4 Assumptions for this simulation are as follow; 1. CO2 in feed gas is removed over 90%. 2. The temperature difference of heat exchanger is over than 10 . 3. When a stream flows in the condenser, the pressure drop is ignored. 4. The pressure drop is 5.0 kPa in the absorber and that of the regenerator is 30.0 kPa. 4. The flow rate of CO2 in feed is 2.10 kgMol/hr. 5. The effect of other components in feed is ignored. 6. The reaction used in this study is as follow.