Integrated Gasification Combined Cycle
- Description
- Benefits
- Process
- Flexibility
- References
Preservation of resources and minimization of pollution are goals that today decisively dictate the development of fossil-fired power plants. Our Siemens integrated gasification combined cycle (IGCC) power plants offer extremely low levels of environmental pollution and are capable of co-firing "dirty fuels" such as low-grade coals, refinery residues, wastes and biomass.
The IGCC plant can achieve major CO2 reduction by effectively capturing the feedstock's carbon inventory from the syngas, before it is combusted in the gas turbine. Captured CO2 can then be buried underground.
By incorporating carbon capture and storage (CCS), a vital technology often known as pre-combustion carbon capture, the IGCC plant successfully meets the energy demand in a low-carbon future. With syngas/hydrogen-capable gas turbines this power plant offers high efficiency levels.
Significant overall integration know-how on the processes that prepare the gasified fuel for combustion enables the design of optimized IGCC plants, the maximization not only of efficiency and low emissions parameters, but also the life-cycle electricity costs and reliability.
Our Siemens IGCC concept, incorporating a Siemens fuel gasifier and a Siemens combined cycle power plant, has the following salient features:
- Syngas/hydrogen-capable gas turbines for IGCC and IGCC CCS plant concepts without or with only partial air-side integration
- High combined cycle power plant efficiencies
- High feedstock conversion during gasification
- Effective integration and coupling of subsystems in terms of process engineering, plant operations and thermodynamic considerations
- IGCC feasibility studies, including gas island consultancy based on thermodynamic modeling, to achieve optimum overall plant performance
- Operation and maintenance for the complete IGCC plant
- Modular IGCC concepts to enable phased construction
- Efficient removal of particulates and other pollutants from the gas to meet all known requirements of environmental protection regulations. In particular, NOx emissions kept below permissible levels without the requirement of further flue-gas treatment equipment.
- Experience gained from earlier IGCC projects such as Buggenum, Puertollano and Plaquemine
Main IGCC Power Plant Subsystems
- Gasification plant including preparation of the feedstock
- Raw-gas cooling via water quench or heat recovery systems
- Optional water-gas shift reactor
- Gas purification system with sulfur removal/recovery and optional CO2 removal
- Air separation unit
- Combined cycle unit with gas turboset, heat recovery steam generator and steam turboset
The gasifier feedstock is converted to synthesis gas (syngas) with the addition of steam and oxygen. Entrained-flow gasifiers for coal are fundamentally well suited to integration in the combined cycle, as are entrained-flow systems for refinery residues. The selection of a specific gasifier type to achieve the best cost, efficiency and emissions levels depends on the type of fuel and the particular application, and must be investigated on a case–by-case basis.
The present Siemens Fuel Gasification (SFG) technology applies the entrained-flow principle, followed by a direct water quench to cool the produced hot raw gas. This technique often used in residue gasification is also suitable for a variety of fuels, in particular coal and petroleum coke. In a further development step, it is possible to capture the sensible heat of the hot raw gas in a syngas cooler to generate high-pressure steam for the steam turbine. Both processes cool the gas sufficiently so that it can be sent directly to the gas treatment system.
Syngas coolers are advantageous when targeting high efficiencies with IGCC plants without CO2 capture (e.g. Buggenum and Puertollano IGCC plants) For IGCC applications with CCS the direct water quench has advantages as the water/steam needed for the shift reaction is already in the raw syngas.
First the particulates, soot and heavy metals are eliminated from the initial raw gas purification downstream of the quench system or syngas cooler. Subsequently chemical pollutants such as H2S, COS, HCl, HF, NH3 and HCN are separated and removed. The separated H2S-rich gas stream is processed to recover saleable sulfur, for example in pure elemental form. Downstream of the gas purification system, the clean gas is mixed with nitrogen (for flow control, flame stabilization and NOx reduction) and/or diluted with water before it is supplied to the gas turbine combustion chamber. In this way, low-level heat can be used efficiently and gas turbine mass flow and output are increased.
In oxygen-blown gasification, the air separation unit (ASU) generates the enriched oxygen supply necessary for the gasification process. The inevitably co-produced nitrogen from the ASU is used primarily in the gas turbine cycle, and, in the case of coal or petroleum coke, smaller amounts are used to transport the solid fuels to the gasifier and for inerting purposes. In addition to air for combustion, the compressor of the gas turbine-generator may also supply all or part of the air for the ASU. Interdependencies between IGCC and ASU are described as air-integrated, nitrogen-integrated or non-integrated respectively.
The steam turbine is supplied with steam from the gas turbine heat recovery steam generator (HRSG). The heat from the raw gas may also be used to generate steam for the steam turbine when gasifiers with high gas outlet temperatures are implemented.
The combined cycle power plant is also well suited to operate on syngas from other non-Siemens gasification processes.
Fuel Flexibility
A great advantage of the Siemens fuel gasifier (SFG) is the wide range of fuels it can handle, including coal, biomass, waste, petroleum coke, refinery residues as well as a blend of these fuels.
In the combined cycle section of the IGCC plant, secondary fuels such as natural gas can be burned (e.g. during the maintenance of the primary fuel supply equipment).
Product Flexibility
The Siemens IGCC concept also offers the possibility of heat generation for process heat and district heat extraction (cogeneration). Alternatively, plants may be optimized for co-production of synthetic fuels such as synthetic natural gas (SNG), Fischer Tropsch products (synthetic gasoline) or hydrogen, or chemicals such as ammonia, urea, methanol, elemental sulfur and sulfuric acid, resulting in a considerable increase in the primary energy utilization factor.
Finally, CO2 can also be separated as a valuable by-product, used for enhanced oil recovery (EOR). For this, CO2 is pumped into largely depleted oil reserves, so that previously unobtainable oil can be extracted, thus extending the life of the source well.
Concept Flexibility
The Siemens syngas turbines enable broad IGCC concept flexibility. The level of integration of air, nitrogen, water and steam can be varied to meet project requirements.
An IGCC plant can be built in phases. For example, it might start with a natural gas combined cycle, with space available for development. Later, a coal gasification and syngas treatment plant can be added, also including CO2 removal equipment which is needed for solutions with carbon capture and storage (CCS). It may prove economically attractive to construct in stages, when fuel prices, CO2 infrastructure or project finance are influential factors. It may also make sense to engineer in readiness for further development, to minimize operational disruption and capital expenditure later on.
Huaneng (Tianjing, China)
Feedstock: Coal
Gasifier: TPRI
Secondary fuel: Fuel oil
Gas turbine (GT): 1 x SGT5-2000E
Air extraction from GT related to ASU/gasifier input: 0%
Air extraction from GT related to GT/compressor flow: 0%
Nitrogen integration: 0%
Net power output: 250 MW
Startup: 2010
EniPower (Sannazzaro, Italy)
Feedstock: Syngas
Gasifier: Shell
Net power output: 250 MW
Gas turbine (GT): 1 x SGT5-2000E
Startup: 2006
ARBRE (Eggborough, UK)
Feedstock: Biomass
Gasifier: CFB
Net power output: 8 MW
Gas turbine (GT): 1 x Typhoon
Startup: 2002
ELETTRA GLT (Servola, Italy)
Feedstock: Coal
Gasifier: Steel Mill
Secondary fuel: Natural gas
Gas turbine (GT): 1 x SGT5-2000E
Air extraction from GT related to ASU/gasifier input: 0%
Air extraction from GT related to GT/compressor flow: 0%
Nitrogen integration: 0%
Net power output: 180 MW
Startup: 2000
ISAB Energy (Priolo Gargallo, Italy)
Feedstock: Asphalt
Gasifier: Texaco
Secondary fuel: Fuel oil
Gas turbine (GT): 2 x SGT5-2000E
Air extraction from GT related to ASU/gasifier input: 0%
Air extraction from GT related to GT/compressor flow: 0%
Nitrogen integration: 0%
Net power output: 521 MW
Net efficiency (LHV): < 40.0%
Startup (natural gas firing): 1998
Startup (syngas): 1999
Elcogas (Puertollano, Spain)
Feedstock: Coal/petroleum coke
Gasifier: Prenflo
Secondary fuel: Natural gas
Gas turbine (GT): 1 x V94.3
Air extraction from GT related to ASU/gasifier input: 100%
Air extraction from GT related to GT/compressor flow: 18%
Nitrogen integration: 100%
Net power output: 300 MW
Net efficiency (LHV): 45.0%
Startup (natural gas firing): 1996
Startup (syngas): 1997/98
Nuon Power (Buggenum, Netherlands)
Feedstock: Coal/biomass
Gasifier: Shell
Secondary fuel: Natural gas
Gas turbine (GT): 1 x SGT5-2000E
Air extraction from GT related to ASU/gasifier input: 100%
Air extraction from GT related to GT/compressor flow: 16%
Nitrogen integration: 100%
Net power output: 253 MW
Net efficiency (LHV): 43.2%
Startup (natural gas firing): 1993
Startup (syngas): 1994/95
STEAG/Kellermann (Lünen, Germany)
Feedstock: Coal
Gasifier: Lurgi
Secondary fuel: Natural gas
Gas turbine (GT): 1 x V93
Air extraction from GT related to ASU/gasifier input: 100%
Air extraction from GT related to GT/compressor flow: 10%
Nitrogen integration: 100%
Net power output: 163 MW
Net efficiency (LHV): 35.1%
Startup: 1972