Integrated Gasification Combined Cycle (IGCC) Technologies

Ting Wang, Gary J. Stiegel

• Publisher: Woodhead Publishing
• Year: 2016
• ISBN:
  9780081001851
• Topic: Technology & Engineering
• Subtopic: Renewable Power Resources
• Index: Technology & Engineering

Integrated Gasification Combined Cycle (IGCC) Technologies discusses this innovative power generation technology that combines modern coal gasification technology with both gas turbine and steam turbine power generation, an important emerging technology which has the potential to significantly improve the efficiencies and emissions of coal power plants.

The advantages of this technology over conventional pulverized coal power plants include fuel flexibility, greater efficiencies, and very low pollutant emissions. The book reviews the current status and future developments of key technologies involved in IGCC plants and how they can be integrated to maximize efficiency and reduce the cost of electricity generation in a carbon-constrained world.

The first part of this book introduces the principles of IGCC systems and the fuel types for use in IGCC systems. The second part covers syngas production within IGCC systems. The third part looks at syngas cleaning, the separation of CO2 and hydrogen enrichment, with final sections describing the gas turbine combined cycle and presenting several case studies of existing IGCC plants.

• Provides an in-depth, multi-contributor overview of integrated gasification combined cycle technologies
• Reviews the current status and future developments of key technologies involved in IGCC plants
• Provides several case studies of existing IGCC plants around the world

1

An overview of IGCC systems

Ting Wang, University of New Orleans, New Orleans, LA, United States

Abstract

The Integrated Gasification Combined Cycle (IGCC) is a complex system, which couples technologies of gasification, gas cleanup, and a gas turbine (GT)/steam turbine combined cycle unit together for the generation of electricity in a more efficient, environmentally benign manner than conventional pulverized coal combustion plants. The gasification unit can convert any carbon-based fuel to synthetic or synthesis gas (a mixture of mainly carbon monoxide and hydrogen, commonly referred to as syngas). Sulfur, trace contaminants like mercury, and even carbon dioxide (if a carbon capture option is selected) are removed prior to fuel combustion in the GT. Because these plants operate at high pressures, the removal of these contaminants is much more efficient, and the capital cost is reduced because of the lower volumetric flow rate of only the fuel gas before combustion, as compared to post-combustion cleanup systems where the combusted gases have a much larger flow rate because they are at an ambient pressure and have more gases than just the fuel gas. The carbon monoxide in the syngas can be shifted in the presence of steam to produce hydrogen and carbon dioxide, which can be separated and removed. The clean syngas or hydrogen-rich gas is fed to the combined cycle unit to generate electricity. This combination of technologies allows for greater fuel flexibility, higher thermal efficiency, and lower emissions compared with today’s coal-fired combustion-based power generation technologies. This chapter provides an overall introduction to the key technologies involved in IGCC plants. Considering that none of these new technologies are sustainable, unless they can be shown to be economically competitive, a summary of various economic analyses is presented. Furthermore, cogasification of biomass and coal is introduced as a means to reduce the effective CO₂ emissions because the CO₂ emitted by biomass is actually carbon-neutral. Finally, the utilization of polygeneration is introduced as a means to create more value-added end products via gasification technology.

Keywords

Integrated; gasification; combined; cycle; IGCC; gasification; gas; cleanup; syngas; carbon; capture; CCS; combined; cycle; power; plant; techno-economic analysis

1.1 Introduction of IGCC

IGCC is an acronym for Integrated Gasification Combined Cycle. The major purpose of IGCC is to use hydrocarbon fuels in solid or liquid phases to produce electrical power in a cleaner and more efficient way via gasification, compared to directly combusting the fuels. The hydrocarbon fuels typically include coal, biomass, refinery bottom residues (such as petroleum coke, asphalt, visbreaker tar, etc.), and municipal wastes. The approach to achieve a “cleaner” production of power is to convert solid/liquid fuels to gas first, so that they can be cleaned before they are burned by removing mainly particulates, sulfur, mercury, and other trace elements. The cleaned gas, called synthetic or synthesis gas (syngas), which primarily consists of carbon monoxide (CO) and hydrogen (H₂), can then be sent to a conventional combined cycle to produce electricity. A simplified IGCC process diagram comprising three major “islands”—gasification, gas cleanup, and power—is shown in Fig. 1.1. The ultimate goal for IGCC is to achieve a lower cost of electricity (COE) than conventional pulverized coal (PC) power plants and/or to be competitive with natural gas-fired combined-cycle systems with comparable emissions.

Figure 1.1 Simplified block diagram of an IGCC system.

While “clean” power generation is the primary driving motivation for entering the business of IGCC, “increasing plant efficiency” to a level higher than that of PC plants is the second driving motivation. To achieve higher efficiency, “integration” between sub-systems becomes necessary. Integration consists of all aspects of the operation, including mechanical, thermal, and dynamic process control. For example, mechanical integration can be achieved between the compressor of the gas turbine (GT) and the air separation unit (ASU), aiming to save some compression power.

Thermal integration can be implemented by strategically interconnecting the various grades of steam generated during the syngas cooling, gas cleanup, and/or water-gas shift processes with the heat recovery steam generator (HRSG) and the steam turbine system. Full air integration does enhance the overall plant efficiency positively by about three to four percentage points, but it also increases the complexity of construction, operation, and maintenance, which may result in increased potential for construction phase delay and/or cost overrun, increased maintenance, lost availability, and degraded reliability. Thus, the concept of nonintegrated IGCC has been advocated by some developers to trade reduced efficiency for higher availability and reliability, even though the term “nonintegrated IGCC” could be confusing.

When the potential of global warming became a concern, the emission of carbon dioxide (CO₂)—a greenhouse gas (GHG)—from power plants was subjected to stringent scrutinization and regulations. Usually, there are three ways to reduce CO₂ emissions: by increasing the overall system efficiency, capturing a portion of the CO₂ and sequestering it, called CCS (Carbon Capture and Sequestration), or utilizing the captured CO₂ multiple times. The syngas generated via the gasification process can be more readily separated into highly concentrated H₂ and CO₂ through the water-gas shift (WGS) process (to be explained later) before the combustion stage (i.e...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• 1. An overview of IGCC systems
• Part I: Fuel types for use in IGCC systems
• Part II: Syngas production and cooling
• Part III: Syngas cleaning, separation of CO2 and hydrogen enrichment
• Part IV: The combined cycle power island and IGCC system simulations
• Part V: Case studies of existing IGCC plants
• Index