Balance of plant (BoP) equipment refers to the auxiliary components in a power plant that support the operation of boilers, turbines and generator equipment. The major components of a BoP system installed in a power plant are coal handling plants (CHPs), ash handling plants (AHPs), water management systems, cooling towers, and electrical BoP (E-BoP) systems. These are integrated into a comprehensive power system package. A brief account of the key BoP system equipment…
Coal handling plant
Coal handling is an integral part of the complete material flow and quality management system. A CHP comprises a proper despatching system for coal transportation as well as a production and control system. The challenges that power plants face in coal handling pertain to management of various grades of coal and oversize run-of-the-mine coal, blending of imported coal with domestic coal and higher unloading capacity optimisation of the CHP layout and costs. Therefore, new CHP plants can be equipped with low capacity variable speed bucket-wheel reclaimers, online coal analysers, pipe conveyors, ship unloaders, wagon tipplers and wind barriers to resolve issues related to blending, coal transportation and coal handling.
Ash handling plant
Indian coal consists of a considerable amount of fly ash for which advanced AHPs need to be installed. AHPs remove ash from furnace ash hoppers, convey this ash by means of a conveyor and finally dispose of the stored ash. Ash handling can be done through mechanical transport, hydraulic transport and pneumatic transport. The mechanical transport system is generally employed for low capacity coal-based power plants wherein hot ash released from boiler furnaces is made to fall over the conveyor belt after cooling and is then transported to an ash bunker and is later dumped. Under the hydraulic transport system, ash is flowed along high velocity water through a channel and finally dumped. The pneumatic transport system can handle abrasive ash and fine dust materials and is preferable for plants that require ash disposal at a distant location. Under this system, larger ash particles are crushed into smaller particles through mobile crushing units and further carried to the conveyor belt through a high velocity stream for final disposal.
Water management system
The water treatment process can be divided into four stages – pretreatment of water, demineralisation, side stream filtration and deionisation. Several new technologies have been developed for water treatment such as ultra high rate solid contact clarifiers for pretreatment, automatic valveless gravity filters (AVGFs) for side stream water filtration, purifying systems for demineralisation, and electrodeionisation systems for electrodeionisation. An ultra high rate solid contact clarifier is a compact, low-cost clarifier for surface water and wastewater clarification. An AVGF is a gravity filter that operates on the loss-of-head principle without using valves, backwash pumps and flow controllers. The demineralisation water system aims to remove mineral salts from water by using the ion exchange process, thus reducing freshwater intake and cutting down overall costs. It consists of rubber-lined pressure vessels connected in series along internal fittings to alter the chemical properties of water to make it fit for use. An electrodeionisation system consists of ion exchange resins and ion-selective membranes to produce high quality distilled water to be used in power plants.
Cooling towers
Cooling towers are heat removal devices that are used to transfer waste heat from power plants into the atmosphere. The large industrial cooling towers used in power plants remove the heat absorbed in circulating cooling water systems, thus making the cooled water suitable for reuse. There are two categories of cooling towers – mechanical cooling towers and natural draft cooling towers. Mechanical cooling towers make use of a fan that forces air through the cooling tower where water falls through a packed heat transfer media. A natural draft cooling tower is a large hyperbolic tower that pulls in air through the stack effect.
Electrical balance of plant
The E-BoP system involves supplying medium voltage, low voltage and direct current power to all loads in the power plant under all service conditions including start-up, operations and shutdown of the plant. E-BoP solutions can support a large range of products from heavy duty turbines to wind and solar applications. E-BoP covers all aspects of a thermal power plant starting from power evacuation to switchyard control and the system is engineered to provide higher reliability and quick returns on investment.
Order intake in the BoP industry has remained sluggish over the past few years. However, as per the Ministry of Power, 22,875 MW of coal-based projects are expected to be commissioned in 2016-17. This additional capacity will provide a boost to BoP order flows, which have remained under pressure in recent years.