Global volatility and high prices of power have significant impact on total power cost of cement plants. In India, most cement plants are operating at very stiff operating margins and are focusing on reducing their operating costs. However, raw material cost cannot be controlled completely.
They can however, improve their operating margins by using cheaper fuels like coal, lignite & pet coke (refinery waste), using fuel flexible fluidised boiler-based power plants. They can further improve the margins and also meet their PAT targets using waste heat recovery option from hot gases emanating from AQC´s and Pre heaters to produce power with zero fuel cost.
Pet coke / coal / lignite as an alternative fuel
Natural gas/oil prices have been particularly sensitive to short-term supply and demand shifts in recent years because of the highly inelastic nature of this market, resulting in increase in the operating cost of the power intensive indutries. Pet coke-a byproduct of delayed coking technology that improves refinery yield has a high calorific value-is an ideal option to reduce the power cost of such energy efficient industries thereby by reducing its operating costs.
Pet coke´s higher sulphur, heavy metal and less volatile matter content in comparison with general fuels, reduction corrosion by hydrogen sulfate and high-temperature oxidation corrosion, which tends to occur on the heat transfer surface, is a challenge however and is known of causing difficulties in stable combustion and operation.
This is where a suitable combustion technology choice and a well designed heat transfer area with good working experience comes in.
Fluidised bed combustion technology is ideal for pet coke due to its long burning process to ensure complete combustion of the low volatile pet coke and its ability to capture a high level of pet coke´s sulphur (typically 5 to 7 per cent) content during the combustion process. The vigorous mixing of the fuel, limestone and ash particles during the low temperature fluidised process allows the fluidised bed combustion-based boilers to cleanly and efficiently burn almost any combustible material while minimising the formation of NOx and optimising the capture of SOx as the fuel burns. The combustion temperature is well below the melting point of the ash, allowing this technology to minimize the corrosion and fouling issues experienced in conventional boilers. For pet coke with high levels of metals (vanadium, nickel, sodium, potassium), CFB technology has demonstrated years of reliable and low maintenance operation.
With high temperature and pressure cycles and large sizes of the boilers successfully designed and in operation, complete utility power requirements of the cement plant can be taken are of with an optimally designed power plant. If there is cooling need, by incorporating vapour absorption chillers, the overall thermal efficiency can be further improved. Today with options of absorption chillers that are direct fired or work on steam, hot water, exhaust gases and a single machine delivering up to 3,500 TR,u sing the last bit of usable enthalpy available, the overall cycle efficiencies can be extremely high.
To incorporate any such engineered solutions, it is important to see the experience of the organisation offering the solution, its expertise in power plant engineering capability apart from its capability to mobilise resources for large projects.
Thermax Limited is a global solution provider in energy & environment engineering with competence in power, heating, combustion, cooling and waste management systems.
Thermax is a leader in captive EPC power generation market in India having in-house manufacturing of key project equipments viz. boilers, electrostatic precipitators and emission control systems, air cooled condensers and water and wastewater solutions. ESP, ACC & water solutions. Backed by experienced professionals, the the power division of the company has contracted more than 100 power and cogeneration projects on a turnkey basis.