Efficiency Of Integrated Gasification Combined Cycle Research Articles

Energy and exergy co-optimization of IGCC with lower emissions based on fuzzy supervisory predictive control

This paper presents an energy and exergy co-optimization method of integrated gasification combined cycle (IGCC) based on Fuzzy Supervisory Predictive Control (FSPC). Firstly, a green IGCC process is proposed which contains three principle couplings: air separation unit (ASU), heat recovery steam generator (HRSG) and CO2 capture/storage unit (CCS). From law of thermodynamics, using substance thermophysical parameters, the energy efficiency and exergy efficiency of IGCC are successively defined. The IGCC power station has features such as closed coupling, large time lag and non-linearity, however, faster response speed and lower overshoot are always the unremitting pursuits. Therefore, the Fuzzy Supervisory Predictive Control (FSPC) method is proposed to implement robust control under complex disturbances by pre-considering unmeasurable disturbance and measurable disturbance. The fuzzy rules extracted from historical bigdata are employed in supervisory layer to make the precise control decisions. Finally, the energy and exergy co-optimization model is built and solved for higher efficiency and economic effectiveness. Taking the large-scale (300MW) IGCC for example, after using FSPC, the efficiency of water recovery is increased from 40.7% to 62.1% with the ratio of 52.6% because of waste water recovery (WWR) system. The net efficiency of proposed IGCC system is increased from 37.6% to 41.7% with the ratio of 10.9%. The exergy efficiency of IGCC system is increased from 36.5% to 39.2% with the ratio of 7.4%. The proposed method has great significance for the energy-saving and Near-zero emissions (NZEC) IGCC with high safety and robust control under supercritical (SC) or ultra-super critical (USC) state.

Conceptual design of membrane-based pre-combustion CO2 capture process: Role of permeance and selectivity on performance and costs

Pre-combustion CO2 capture is regarded as a promising option to mitigate the environmental pollution from coal combustion, due to its relatively low energy duty and prospects for the use of hydrogen in power generation and industrial sectors. Nowadays, research and development efforts are mainly focusing on advanced technologies to separate H2 and CO2 from a synthesis gas of a gasification-based power generation system. In this regard, membrane separation processes are attracting an increasing attention, due to their potential for a more cost-effective and environmental friendly CO2 capture compared to well-established solvent-based processes.A conceptual design and techno-economic analysis is presented of a pre-combustion CO2 capture process based on H2-selective polymeric membranes in an integrated gasification combined cycle (IGCC) power plant, including the water-gas-shift (WGS) system. The design approach is based on the selection of the most effective membrane separation process and economic optimization of operating conditions. The capture process is based on a three-stage membrane separation system, producing a hydrogen stream feeding the power generation unit and a liquid CO2 stream, ready for transport and geological storage. Considering a state-of-the-art polymeric membrane with a H2 to CO2 selectivity of 15 and H2 permeance of 300 GPU, the IGCC efficiency penalty states at around 5% pts when the separation process is operated with a pressure on membrane feed side of 70 bar, corresponding to an estimated cost of CO2 capture of 16.6 €/t CO2. A sensitivity analysis of operating pressure and membrane properties revealed that the cost of CO2 capture can be reduced to less than 15 €/t CO2 by moderately increasing the H2 to CO2 selectivity and adjusting the designed process accordingly. Additionally, a decrease in the feed-side pressure slightly disfavours the economic performance of CO2 capture for H2 permeances greater than 300 GPU. The membrane-based capture process compared most favourably in cost-effectiveness with the well-established solvent based Selexol process.

Technological solutions for an advanced IGCC plant

The paper studies the basic methods offered by different sources for raising the efficiency of the air-blown integrated gasification combined cycle (IGCC). The technological solutions that can minimise the efficiency gap between IGCC and natural gas combined cycle (NGCC) were selected. The flow diagram for an air-blown IGCC is proposed which ensures cycle efficiency and exceeds that of O2-blown IGCC owing to a decreased need for fuel gas. The proposed scheme would enable the approximation of the cycle efficiency to NGCC. The role of integration linkages in raising the efficiency of IGCC was also assessed. Thermodynamic models for the basic elements of IGCC were developed. We calculated the efficiency of steam-air blast and cycle air heating during cold fuel syngas clean-up using IGCC with an M 701F4 gas turbine that runs on syngas processed from Kuznetsk bituminous coal as a model. We also established that steam-air blast heating increases the heat value of fuel gas by 10%, conversion efficiency by 84.2%, and gross/net efficiency of IGCC by 0.44/0.53%. Steam-air blast and cycle air heating decreased coal consumption for gasification by 44% and led to an additional increase in gross/net efficiency by 0.77/1.06%. The solutions proposed in the paper enable the creation of a flowchart for IGCC with F-class gas turbine and one gasifier with a capacity of 2000 t/d for coal and gross/net efficiency of 52.47/50.64%.

IGCC Precombustion CO2 Capture Using K2CO3 Solvent and Utilizing the Intercooling Heat Recovered From CO2 Compressors for CO2 Regeneration

CO2 capture (CC) using hot K2CO3 solvent in integrated gasification combined cycle (IGCC) plant is a promising technology for CO2 emission reduction. Based on pilot scale trials, an innovative IGCC system with CC using hot K2CO3 solvent is proposed, in which the intercooling heat between CO2 compressors is recovered for CO2 regeneration (IGCC + CC + HR). Thermodynamic performance and exergy and energy utilization diagram (EUD) analysis are presented. Results show that recovery of the intercooling heat between CO2 compressors reduces the steam extraction requirement from turbines for CO2 regeneration by around 18% and enhances the efficiency of IGCC with CO2 capture (IGCC + CC) plant by 0.3–0.7 percentage points. With 90% CC, the efficiency of the IGCC + CC + HR plant is around 35.4% which is higher than IGCC + CC plant using Selexol technology. Compared to IGCC, the energy penalty for CC in IGCC + CC + HR plant is mainly caused by the exergy losses in CO2 separation (45.2%), water gas shift (WGS) (28.5%), combined cycle (20.7%) and CO2 compression units (5.6%). EUD analysis shows that the IGCC + CC + HR plant realizes good match of the energy levels between the intercooling heat and the recovered steam for CO2 regeneration, thereby obviously reducing the exergy losses in CO2 compression and separation units and improving the plant efficiency. The results presented in this paper confirm the sources causing the energy penalty for CC in IGCC power plant and the new IGCC + CC + HR system helps to reduce the energy penalty for CC in IGCC power plant based on solvent technologies.

Process Analysis Study of Integrated Gasification Combined-Cycle with CO2 Capture

The present study adopted commercial chemical process simulator, Pro/II® V8.1.1, to analyse the system performance of Integrated Gasification Combined-Cycle (IGCC) with CO2 capture. There are four major blocks in a reference IGCC plant, i.e. air separation unit (ASU), gasification island, gas clean-up unit, and combined-cycle power block. Additional water gas shift reaction and CO2 absorption processes are integrated into the gas clean-up system for CO2 capture. The feedstock is Kaltim Prima Coal (KPC) from Indonesia, which is generally used in Taiwan, to evaluate the data with actual situation in Taiwan. The results show that the efficiency of IGCC is around 42.22% (HHV). When 90% CO2 capture is employed in the IGCC, the efficiency is decreased to around 36.74% (HHV). It means that the energy penalty of 90% CO2 capture is about 5.48 percentage points. Furthermore, data of 50% CO2 capture is evaluated to reach the CO2 emission condition close to that of Natural Gas Combined-Cycle (NGCC).

Exergy analysis of two cryogenic air separation processes

Two process designs of a cryogenic ASU (air separation unit) have been evaluated using exergy analysis. The ASU is part of an IGCC (integrated gasification combined cycle); it is supplying oxygen and nitrogen to the gasifier and nitrogen to the gas turbine. The two process designs separate the same feed into products with the same specifications. They differ in the number of distillation columns that are used; either two or three. Addition of the third column reduced the exergy destruction in the distillation section with 31%. Overall, the three-column design destroyed 12% less exergy than the two-column design. The rational exergy efficiency is defined as the desired exergy change divided by the total exergy change; it is 38% for the three-column design and 35% for the two-column design. Almost half of the exergy destruction is located in compressor after-coolers. Using this heat of compression elsewhere in the IGCC can be an important way to increase the IGCC efficiency. It is proposed to use it for the pre-heating of ASU products or for the production of steam, which can be used as part of the steam turbine cycle.

Gas Turbine Combustion and Ammonia Removal Technology of Gasified Fuels

From the viewpoints of securing a stable supply of energy and protecting our global environment in the future, the integrated gasification combined cycle (IGCC) power generation of various gasifying methods has been introduced in the world. Gasified fuels are chiefly characterized by the gasifying agents and the synthetic gas cleanup methods and can be divided into four types. The calorific value of the gasified fuel varies according to the gasifying agents and feedstocks of various resources, and ammonia originating from nitrogenous compounds in the feedstocks depends on the synthetic gas clean-up methods. In particular, air-blown gasified fuels provide low calorific fuel of 4 MJ/m3 and it is necessary to stabilize combustion. In contrast, the flame temperature of oxygen-blown gasified fuel of medium calorie between approximately 9–13 MJ/m3 is much higher, so control of thermal-NOx emissions is necessary. Moreover, to improve the thermal efficiency of IGCC, hot/dry type synthetic gas clean-up is needed. However, ammonia in the fuel is not removed and is supplied into the gas turbine where fuel-NOx is formed in the combustor. For these reasons, suitable combustion technology for each gasified fuel is important. This paper outlines combustion technologies and combustor designs of the high temperature gas turbine for various IGCCs. Additionally, this paper confirms that further decreases in fuel-NOx emissions can be achieved by removing ammonia from gasified fuels through the application of selective, non-catalytic denitration. From these basic considerations, the performance of specifically designed combustors for each IGCC proved the proposed methods to be sufficiently effective. The combustors were able to achieve strong results, decreasing thermal-NOx emissions to 10 ppm (corrected at 16% oxygen) or less, and fuel-NOx emissions by 60% or more, under conditions where ammonia concentration per fuel heating value in unit volume was 2.4 × 102 ppm/(MJ/m3) or higher. Consequently, principle techniques for combustor design for each IGCC were established by the present analytical and experimental research. Also, this paper contains some findings of the author’s previously published own works and engages in wide-ranging discussion into the future development of gasification technologies.

Integrated gasification combined cycle (IGCC) process simulation and optimization

The integrated gasification combined cycle (IGCC) is an electrical power generation system which offers efficient generation from coal with lower effect on the environment than conventional coal power plants. However, further improvement of its efficiency and thereby lowering emissions are important tasks to achieve a more sustainable energy production. In this paper, a process simulation tool is proposed for simulation of IGCC. This tool is used to improve IGCC's efficiency and the environmental performance through an analysis of the operating conditions, together with process integration studies. Pinch analysis principles and process integration insights are then employed to make topological changes to the flowsheet to improve the energy efficiency and minimize the operation costs. Process data of the Texaco gasifier and the associated plants (coal preparation, air separation unit, gas cleaning, sulfur recovery, gas turbine, steam turbine and the heat recovery steam generator) are considered as a base case, and simulated using Aspen Plus ®. The results of parameter analysis and heat integration studies indicate that thermal efficiency of 45% can be reached, while a significant decrease in CO 2 and SO x emissions is observed. The CO 2 and SO x emission levels reached are 698 kg/MWh and 0.15 kg/MWh, respectively. Application of pinch analysis determines energy targets, and also identifies potential modifications for further improvement to overall energy efficiency. Benefits of energy integration and steam production possibilities can further be quantified. Overall benefits can be translated to minimum operation costs and atmospheric emissions.

증기연계 공정을 가지는 석탄가스화 복합발전플랜트의 성능해석

Waste heat recovery process designs and performance analyses are conducted on the IGCC(Integrated Gasification Combined Cycle) power plants integrated with two different coal gasification and gas cleanup processes by Shell and GE/Texaco. Through the analysis results, the present study provides the steam integration concept between the HRSG and the chemical processes of IGCC power plant, and investigates the effect of steam integration on the power generation of IGCC power plant. The present simulation results show less steam power output and higher overall IGCC efficiency of the Shell-based power plant than the GE/Texaco.