Improving energy efficiency
On an average, the cement plants are spending 35 to 50 percent of total manufacturing cost of cement to meet their energy demands. In fact, the cost of energy is a very important factor in the price of cement.
Modern cement plant consumes around 65 to 75 kWh of electrical energy for production of one ton of cement. All most around 60 percent of electrical energy is consumed by kilns and mills in the plant. As we look at older plants by way of the age of these plants the energy consumption goes up to 80 to 100 kWh per tonne of cement.
Indian cement plants consume around 723 kcal/kg of thermal energy for producing 1 kg of clinker. The major use of heat energy is in kiln and pre-calciner of the kiln system. The heat energy converts the powder form of raw materials into clinkerk, which is an intermediate product. Conversion of lime stone to clinker is the most energy consuming stage in cement production. The developments in the kiln systems have always helped cement industry to reduce energy consumption. The energy consumption in the cement sector of India can be compared to any of the best operating plant in the world. Ambuja cement, Dalmia Bharat and UltraTech plants are the trendsetters for Indian cement sector. Our cement industry has been go getter in assimilating new technologies, which lead to improvements in energy consumption year after year.
Waste heat recovery system (WHRS)
This technology has been now adopted by almost all the cement plants. The technique used is very simple to understand but intricate to implement. The hot gases generated by preheater and by cooler are taped and used to produce power by installing a heat recovery boiler and turbine. If the plant has got very high moisture in raw materials and the energy is utilised for drying of slag or fly ash, then the energy generated by WHRS is always compromised. In the large plants energy of about 22-36 kWh/ tonne of clinker can be generated.
A two-pronged dilemma faces the Central Government. Should it exempt industrial units cogenerating power from renewable purchase obligation (RPO)? And, should it leave it to the States to interpret the meaning of renewable energy from its policies on cogeneration? Many industrial units in the cement, steel and other sectors, which use coal or natural gas as primary fuel, have been demanding exemption from RPO. The obligation makes it necessary for such units to meet part of their power needs from renewable sources. Many of these units, which have filed petitions with their respective state electricity regulatory commissions, want that energy produced through the WHR system should be considered valid for meeting the obligation. The WHRS recovers heat from high energy content of exhaust gases. In its policy for Captive & Co-generation Plants, 1996, the Ministry of Power defines cogeneration facility as a unit that simultaneously produces two or more forms of useful energy, such as electric power and steam. Industrial units use this energy to generate power or in various industrial processes, thus increasing its efficiency and saving costs. However, the Ministry of New and Renewable Energy (MNRE) accepts cogeneration only as part of biomass utilisation, specifically focused on bagasse-based cogeneration in sugar mills. It does not accept any other form of cogeneration as renewable energy. Clearly, the Centre needs a policy that can lift the cloud of confusion.Though more and more cement plants are opting for WHRS, if the above confusion is removed, the number will increase many folds.
False air intrusion
The other unattended area where we would like to draw the attention of our readers is false air. In the current issue we have included an article from one of the experts of the subject. False air is any unwanted air entering into the process system. The exact amount of false air is difficult to measure. However, an indicator of false air can be, increase of percent of oxygen between two points (usable for gas stream containing less than 21 percent of oxygen).
Due to unwanted air, the power consumption increases and system's temperature decreases. Therefore, to maintain the same temperature fuel consumption has to be increased. There are several points in the process from where the false air can enter. It is possible to measure false air by various scientific methods the entry points and quantum of false air.
There are innovative, cost effective and long lasting products available which do not deteriorate with pressure or temperature and can produce better results. There is always a hidden potential that exists in every plant which needs to tap to save energy.
Installation of medium voltage variable frequency drive
Induction motors are used in cement plant for driving fans like pre heater, cooler vent, mills etc. Lot of power is lost in these applications which can be saved by using slip power recovery system and installing variable frequency drives.
Installation of high efficiency separators
Separator by definition is the equipment that is used to separate fine particles from coarse material. Usually a stream of fine particles is collected as a product and the coarse material is send back for grinding again. The efficiency of a separator is judged by how much percentage of fine particles get associated with coarse material it should be less than 10 to 15 percent. An efficient separator avoids over grinding of fine particles and reduces the power consumption. An efficient grinding system should have less number of circulations of the mill feed that leads to reduction in the energy demand of the grinding system. This results in reduction of specific energy demand in the grinding circuit.
Perform, Achieve, Trade (PAT) Scheme
The Perform, Achieve, Trade (PAT) scheme was established by National Mission for Enhanced Energy Efficiency. It is regulatory instrument to reduce specific energy consumption in energy intensive industries, with an associated market based mechanism to enhance the cost effectiveness through certification of excess energy saving which can be traded.
The first cycle of the PAT Scheme (2012-2015) managed to reduce the energy consumption of more than 400 energy-intensive enterprises (known as Designated Consumers -DCs) by 5.3 percent, above the initial target of 4.1 percent. Overall, majority of the DCs implemented relatively low cost measures, such as changes to process control and installation of variable speed drives on electric motors, which were financed through the DCs own resources. In terms of sector specific interventions, for example, in the cement industry the most common measures covered installation of waste heat recovery systems and vertical rolling mills.
The trading of energy saving certificates (ESCerts) is central to the PAT programme and serves as an incentive to reach or surpass the mandatory targets. The Bureau of Energy Efficiency is the administrator and developed a platform to manage the ESCert trading process. The demand for ESCerts is expected to be relatively low, given that about 3.8 million ESCerts have been issued of which about 1.5 million need to be absorbed by the DCs who are falling short of targets.
Improving TSR numbers
The use of alternate materials as a replacement of fuel is at very early stage in our country. Several reasons can be put forward to justify that. But the passing and implementing of GST laws, slowly the things are improving. As the Thermal Substitution Rate (TSR) numbers will go on improving the energy consumption in the cement industry is set to change. Until then we keep our fingers crossed.
- VIKAS DAMLE