Fresh Air Dampers and heat exchangers are taking care of pollution control at high temperature environment.
The cement industry and the environmental regulators have been going through a very uneasy relationship over the last 2 decades. As only to be expected, the industry has a diverse mix of vintage, old, modern and ultra modern plants, and understandably with starkly different capabilities on environmental front.
Tough environmental norms were first promulgated in 1980, the Ministry of Environment, Forest & Climate Change (MoEF&CC) has notified the new pollution norms for the Indian cement industry in May 2016, with the primary aim of minimising pollution, in line with the country's intent/commitments made at CoP21 at Paris last year. The deadline for which was set at March 31, 2017.
The new norms have made particulate matter (PM) emissions stringent by bringing them from 50-150 milligrams per cubic meter (mg/Nm3) to 30 mg/Nm3. This limit depends upon the age and location of the plant.
The new norms relaxed the emission limit of sulphur dioxide and nitrogen oxide, one of the two key polluting gases released from industries. The limit of sulphur dioxide emitted from a cement plant was increased from 100 mg/Nm3 to 100-1,000mg/Nm3. This limit depends on sulphur content in limestone, a raw material for making cement. The limit for nitrogen oxide was relaxed from 600 to 800 mg/Nm3 to 600-1,000 mg/Nm3.
Most of the pollutants are primarily generated from the burning of municipal waste, hazardous waste as well as the waste from cement plants. Though electro static precipitators (ESPs) were being used a couple of decades back, now new technologies have become popular among manufacturers.
Cement manufacturing is a high temperature process and excess heat is often used for the drying of raw materials. 'Fabric filter is a preferred technology to meet extremely low emissions and it also handles the future need for multi-pollution control solutions including Respiratory Suspended Particulate matter (RSPM)-PM2.5,' says Anilkumar Mukundan, Head - Customer Service Projects, FLSmidth, a leading manufacturer of pollution control equipment for the cement industry.
Conventional fabric filter handles flue gas temperature up to 200 Degree Celsius, while glass bags with e-PTFE membrane can handle up to 260 Degree Celsius.
When temperature exceeds 200 Degree Celsius, we offer glass bags with e-PTFE membrane, which can handle up to 260 Degree Celsius. The ambient dilution air is added using FAD (Fresh Air Damper) and heat exchangers are used for higher temperature environments in a cement plant.
- B.S. Srinivasalu Reddy