Appendix 3 IGCC with CO2 Capture Process Summary

Gasification technology

Gasification technology and Wandoan Power

Introduction

Gasification is a process that converts carbon-containing materials, such as coal, to a syngas which can be used as a fuel in a gas turbine to produce electricity or as feedstock to produce products such as chemicals, fertilisers, a natural gas substitute, hydrogen and transportation fuels.

The Wandoan Power Project (Wandoan Power) will use GE's commercially available gasification and power technologies configured as an integrated gasification combined cycle (IGCC) plant integrated with pre-combustion carbon capture technology. The main process blocks are illustrated in Figure 5.1 and described at a high level in the remainder of Section 5.1. Further detail is provided in Section 7 of this report.

GE's gasification technology is discussed generally in section 5.2.

Figure 1 - Wandoan IGCC with CO2 capture process

Coal is crushed and mixed with water then injected as a slurry with oxygen into a high temperature pressurised reactor, the gasifier. The conditions inside the gasifier break apart the chemical bonds of the coal slurry feedstock, forming a raw syngas which consists primarily of hydrogen and carbon monoxide together with smaller quantities of methane, carbon dioxide, hydrogen sulphide, and water vapour.

The gasifier also produces slag which is a black glass-like by-product composed primarily of sand, rock, and minerals from the feedstock. Slag has potential for beneficial use e.g. road base or sand blasting.

Air separation unit

An air separation unit (ASU) uses electrical power from the power station to extract from atmospheric air two elements: oxygen and nitrogen. Oxygen is input to the gasifier (instead of air) to improve the gasification reaction. Nitrogen is used as a diluent for the syngas sent to the gas turbine.

Syngas clean-up and CO2 capture

Raw syngas is cleansed by various processes to remove CO2 and impurities such as particulates and sulphur. Elemental (yellow) sulphur is captured with a sulphur recovery unit (SRU) to become an economic by-product.

The water-gas shift reaction is used to increase the level of CO2 available for capture. In the acid gas removal (AGR) stage a solvent is used to remove acid gas and CO2 from the syngas. The captured CO2 stream is dehydrated and compressed ready for transport by pipeline to a storage site.

A clean hydrogen-rich syngas stream is sent as fuel to the combustion turbine for power generation. The clean syngas is then used as the fuel for the gas turbine.

Power plant

The power plant combines a gas turbine and a steam turbine into a combined cycle unit.

Clean syngas from the gasification process area is combusted in the gas turbine to produce electricity. After carbon capture the syngas has a high level of hydrogen compared to normal syngas or natural gas. nitrogen (from the ASU) is used as a diluent to regulate the level of hydrogen in the clean syngas. The gas turbine is a standard GE 9F adapted to operate on a mix of high hydrogen syngas and nitrogen.

The excess heat from both the gas turbine and the gasification reaction is then captured using a heat recovery steam generator (HRSG). This steam is sent to a steam turbine to produce additional electricity.