Transport Gasifier Based IGCC System Integration Analysis

IGCC technology is recognized as one of the most promising clean coal technologies while transport gasifier can gasify the coal of high ash and high ash fusion point efficiently. This paper will investigate the integration aspects of transprot gasifier based IGCC system which intends to get some useful suggestions for the optimization of the IGCC power plant. The contents include five parts as follows:1. Key components models of IGCC systemAs the basis of system analysis, the components models of IGCC are built including transport gasifier, low calorific gas turbine and its NO_x emission, high and low pressure air separation units etc. The models are verified and show reasonable results thus can be used for the analysis of IGCC system.2. Integration of gas turbine and air separation unitVarious integration options between the gas turbine and air separation unit are analyzed including gas turbine air extraction, ASU nitrogen reinjection and the combination of the two options. The gas turbine characteristics, NOx constrain and the pressure of the ASU are considered in the system analysis. The affects of gas turbine air extraction and ASU nitrogen reinjection to IGCC performance is analyzed and some suggestions about the integration of gas turbine and ASU are obtained.3. The effects of unit processes on the performance of IGCC systemThe quench process and the process with syngas coolers are compared and how steam parameter and outlet syngas temperature affect the system thermal efficiency are analyzed. Results show that with a syngas cooler producing high pressure steam, IGCC system can achieve much higher efficiency than the quench process. While the efficiency is almost the same whether saturated high pressure steam or superheated steam is produced. Besides that, for a system with NO_X reduction by steam injection, the equipment of an economizer at the downflow of the syngas cooler seems not necessary.Low temperature heat utilization of the syngas is discussed and five cases are compared. Results show that by fuel saturation and condensate preheating, the low temperature heat of the syngas can be used efficiently and improve the system efficiency by 1.21 percent. How the fuel saturation benefits the IGCC system is studied and compared to steam injection method when using water as the dilution to reduce NO_x emission of the gas turbine. The fuel saturation show more favorable performance than steam injection. The comparison of oxygen blown transport gasifier and air blown gasifier show that IGCC based on an air blown gasifier has higher efficiency, more power output and lower NO_x emission. Finally different particulate removal methods are compared, and the results show that system with a dry filter has higher efficiency of 1.81 percent than that with a wet scrubber particulate removal.4. Gas turbine performance when firing low calorific coal gasA method to calculate the turbine cooling flow is given and the performance of PG9351FA gas turbine when firing typical low calorific coal gases is calculated. Various methods to increase the surge margin and to decrease the power output are compared including compressor pressure ratio increase, compressor flow reduction, turbine critical area increase, turbine inlet temperature decrease and the compressor air extraction. Results show that to close the IGV can reduce the power output of gas turbine but have little effect on the increase of surge margin. When firing syngas produced by oxygen blown transport gasifier with no dilution, the gas turbine power and surge margin can meet the requirement. While firing syngas produced by an air blown transport gasifier, the compressor air extraction is suggested for the operation of gas turbine.5. Retrofit natural gas combined cycle power plant with IGCCThree IGCC processes based on transport gasifier to retrofit existing natural gas combined cycle power plant is designed and analyzed. Results show that the gas turbine combined cycle can operated independently and need not to be modified significantly, and the system can achieve the overall efficiency of over 40%.