Natural Gas Applications and Integrated Gasification Combined Cycle
Applications and Processing of Natural Gas
Natural gas can be used directly as a fuel or as synthesis gas for the petrochemical industry. The transformations and products available are the same as those obtained from synthesis gas derived from crude oil refining. Natural gas is the cleanest natural fuel from a pollution standpoint, as it produces the least amount of CO2 per unit of energy of all fossil fuels. However, it is more difficult to store and transport than solid and liquid fuels.
Because it mixes better with air, natural gas requires less air to achieve complete combustion. This saves energy and allows for better regulation and heat transfer. It also allows for control of flame shape and, therefore, better control of process temperature and specific power. As natural gas is less dense than air, leaks tend to disperse into the atmosphere and are not likely to accumulate in low-lying areas, reducing the risk of flammability in hazardous locations. In industrial settings, natural gas is received ready for immediate use, eliminating the need for pumping or heating facilities or the use of additives. Thermally insulated pipelines are also unnecessary.
Advantages of Natural Gas as Fuel
The main advantages of natural gas as a fuel, compared to other fossil fuels, are:
- Combustion products have a low content of sulfur compounds, which lowers the temperature of those emissions, improving performance, and eliminating corrosion in the smoke damper.
- Combustion products have no harmful effects on the products being heated, making it possible to use natural gas directly on food products, ceramic glazes, etc. It also prolongs the life of refractories.
- The absence of ash keeps exchange surfaces clean, improving performance and reducing maintenance.
Moreover, the efficiency of a gas boiler is around 71%, which is very high compared to that obtained by using natural gas to produce electricity (40%). Using this electricity to produce heat further lowers efficiency. It is more appropriate to use natural gas for heating in the domestic sphere and to produce heat and power (CHP) in industry.
Integrated Gasification Combined Cycle (IGCC)
IGCC plants consist of two major facilities:
- The gasification plant, which produces synthetic gas.
- The combined cycle plant, which produces electricity using a gas turbine and a steam turbine.
The product resulting from the gasification of other fuels—mostly coal or petroleum coke—is used as fuel for a gas turbine. This process takes place at the station and then utilizes residual heat by feeding a boiler to power a steam turbine. The final power produced is, therefore, the sum of that generated in the steam cycle and the gas turbine.
Benefits of IGCC
The benefits of IGCC technology include improved conversion efficiency (about 45% compared to the typical 38%), which not only reduces the cost of electricity produced but also the amount of carbon dioxide emitted per kWh of power produced.
IGCC Process
In an integrated gasification combined cycle plant, coal is transported and unloaded by trucks at the plant’s coal yard. From the yard, a conveyor belt sends the coal to the fuel preparation plant, where it is sprayed and dried. This plant also cleans and cools the air to obtain oxygen, which is used for coal gasification, and nitrogen, which increases the gasifier’s performance.
The gasifier receives the pulverized fuel from the preparation plant. By injecting oxygen and water vapor at the bottom, a synthetic gas is produced at a very high temperature. The heat from this gas contributes to the water cycle and generates steam, which expands the steam turbine. Once the synthetic gas cools, the existing solid ash can be separated.
Before being burned, the gas obtained in the gasifier passes through the desulfurization unit, where sulfur is removed. Once clean, the gas is sent to the gas turbine. The gas turbine consists of a gas compressor that takes in outside air and adapts it to the conditions necessary for optimal combustion, a combustion chamber where the gas is burned, and the gas turbine itself, in which the combustion gases expand and drive an electric generator. The electric power generated is sent to high-voltage processors in the park to adjust its voltage and current conditions for high-voltage transmission.
The recovery boiler utilizes the residual heat from the combustion gases from the gas turbine before they are released into the atmosphere, producing steam at different pressures. This steam is then sent to the steam turbine. As previously mentioned, the gasifier boiler also produces steam, taking advantage of the high temperature at which synthesis gas is generated to vaporize the preheated water in the recovery boiler.
As in the case of the gas turbine, the steam turbine drives a generator that produces electricity, which is then sent to the high-voltage network for transmission. The steam exiting the turbine is condensed by exchanging heat with cooling water. This water is sent to the cooling tower to release the absorbed heat. The plant’s liquid waste is treated in an effluent treatment plant.