Combined plants power generation

Today, Low-Btu Gas (LBG) is expected to be preferred in small demand applications for single users located outside of downtown metropolitan areas. Specific industries in which LBG is expected to be most competitive include primary metals, iron ore beneficia-tion, metal finishing, lime brick refractory, and food industries. Another potential market for Low-Btu Gas is in combined cycle power generation. Cleaned Low-Btu Gas may be particularly advantageous when a plant has many separate combustors which, because of the anticipated new environmental standards, would require either multiple scrubbers or a flue gas collection system. Cleaned Low-Btu Gas is also one of the few options available to a user planning a plant expansion in a non-attainment area. 

In contrast, gasification systems are far more efficient, reaching 60 percent, versus only 20-40 percent for some direct-fired plants.31 These types of systems heat the biomass in an environment where the solid biomass breaks down into a flammable gas, such as methane.This gas can then be used in more efficient combined-cycle power-generation systems... 

Coal gasification may likely find future application in methanol production for utilization in combined cycle power generation facilities. In this case, the methanol (stored on-site as a liquid) will be utilized as a peak shaving fuel and will be produced from excess ifier capacity as power demand is reduced. Several different schemes have been proposed for combining methanol production with coal ification in a power plant scenario. This particular arrangement may be most favorable for a liquid-phase process (see reference to the Air Product process in Sec. 3.2.7) that can utilize a substoichiometric feed with a reasonable once-throu conversion while passing on unconverted gas to the combined cycle gas turbine as a fuel... 

Methanol, a clean burning fuel relative to conventional industrial fuels other than natural gas, can be used advantageously in stationary turbines and boilers because of its low flame luminosity and combustion temperature. Low NO emissions and virtually no sulfur or particulate emissions have been observed (83). Methanol is also considered for dual fuel (methanol plus oil or natural gas) combustion power boilers (84) as well as to fuel gas turbines in combined methanol / electric power production plants using coal gasification (85) (see Power generation). 

In apphcation to electric utihty power generation, MHD is combined with steam (qv) power generation, as shown in Figure 2. The MHD generator is used as a topping unit to the steam bottoming plant. From a thermodynamic point of view, the system is a combined cycle. The MHD generator operates in a Brayton cycle, similar to a gas turbine the steam plant operates in a conventional Rankine cycle (11). 

The next generation of gas turbine-based, combined-cycle power plants, under constmction in many parts of the world, is to feature net plant efficiencies in the 60% range based on LHV of fuel input. These faciUties, scheduled for start-up in the latter 1990s, are anchored by large gas turbines capable of simple-cycle efficiencies >40% LHV in some cases. To develop these machines, manufacturers have scaled up and improved upon designs that have already proved to be highly rehable. 

As of the mid-1990s, many older conventional steam plants have been converted to combined cycle. The old boiler is removed and replaced by a combustion turbine and heat recovery steam generator. Although the cycle efficiency is not as high as completely new plants, substantial capital cost is avoided by the modification and reuse of existing steam turbine and auxiHary equipment. In many combined cycle power plants, steam is injected into the combustors of the combustion turbine to lower peak flame temperatures and consequendy lower NO. ... 

For most chemical plants, process steam is used at pressures of 1.825 MN/m" (250 psig), saturated or lower. When combined heat and power generation is economically justified, the steam may be generated at about 5.96 MN/m" (850 psig) appropriately superheated and used to drive back-pressure steam turbines passing out process steam at the required pressure level. 

Both the Power Industry and the petrochemical industries use the aircraft-type turbine. The Power Industry uses these units in a combined cycle mode for power generation especially in remote areas where the power requirements are less than 100 MW. The petrochemical industry uses these types of turbines on offshore platforms especially for gas re-injection, and as power plants for these offshore platforms, mostly due to their compactness and the ability to be easily replaced and then sent out to be repaired. The aeroderivative gas turbine also is used widely by gas transmission companies and petrochemical plants, especially for many variable speed mechanical drives. These turbines are also used as main drives for Destroyers and Cruise Ships. The benefits of the aeroderivative gas turbines are ... 

Boyce, M.P., Performance Monitoring of Large Combined Cycle Power Plants, Proceedings of the ASME 1999 International Joint Power Generation Conference, San Francisco, California. Vol. 2, pp. 183-190, July 1999. 

Boyce, M.P., Performance Characteristics of a Steam Turbine in a Combined Cycle Power Plant, Proceedings of the 6th EPRI Steam Turbine Generator/ Workshop, August 1999. 

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