Energy-efficient cupola and pollution control system for foundry units

Energy-efficient cupola and pollution control system for foundry units

The new age cupola

Dirty grey and smoky black. For people staying in Howrah, this was the most befitting, if not the most enlivening, description of the sky. Closer inspection could have revealed that some of these fumes emanated from clusters of small-scale foundry units, specially because Howrah houses India's largest foundry cluster. With environmentalists ringing the alarm bell and the law-enforcement agencies getting stringent by the day, the writing on the wall became clearer.

Thinking out of the box

Behind the smokescreen was a scenario that required a sustainable and practical solution which would not risk the closure of about 3500 foundry units across India that produced grey iron castings. Dwindling profit margins had anyway been threatening these traditional foundries for some time. Studies conducted by TERI revealed that the cupolas (the predominant melting furnaces) being used were substantially responsible for the dismal energy and environmental performance of the foundries. TERI, with the support of the SDC (Swiss Agency for Development Cooperation), and in collaboration with ABB India, Sorane SA, Switzerland, and Castings Development Centre, UK, demonstrated an energy-efficient design of the cupola and a pollution control system for Indian foundries. This was the answer to the needs of the foundry owners and environmentalists alike.

The challenge

Despite being the most important secondary metallurgical processing industry in the small-scale sector, these foundries are highly labour-intensive with low-levels of mechanization. Primarily family-owned and managed, they directly employ half a million people and produce about 3 million tonnes of castings annually. TERI has undertaken an initiative that aims at turning around the conventional cupola furnaces of this industry so as to make them environment friendly, energy-efficient, and profitmaking. Incorrect selection of the blower, improper distribution of air, lack of control on feed materials, and poor operating and maintenance practices were identified as some of the reasons behind the poor energy performance of conventional cupolas.

To make matters worse, SPM (suspended particulate matter) emissions from these cupolas were higher than the permissible environmental standards, because of the lack of effective gas-cleaning devices.

Breaking new ground

Figure 1 Demonstration plant in Howrah

TERI developed an improved cupola prototype that took into account all the failings of the previous design of the cupola, the DBC or the divided blast cupola. It is different from its infamous predecessor in that it supplies air blast at two levels. These, in tandem with other optimized design modifications in the DBC and a venturi scrubberbased pollution control system, are responsible for its energy efficiency and minimal polluting nature.

Not only did the workers breathe a sigh of relief but the owners of the most efficient foundries also saved up to 25% in coke; the least energy-efficient plants saved coke up to an impressive 65% . Usually, the savings from coke pay for a new DBC within a year. Additional benefits include lower oxidation losses of silicon and manganese and a reduction in rejection levels. The pollution-control system brings down the quantum of SPM released into air —from a range of 1300–3900 mg/Nm³ (milligram per normal cubic metre) to about 50 mg/Nm³ . The SO2 emissions are brought down from the prescribed 300 mg/Nm³ to 40 mg/Nm³.

Percentage of coke saving in cupola by adoption of divided blast cupola
A comparison of emission levels

Applications/benefits

The capital investment for the DBC, inclusive of all civil work, platforms, and a bucket charging system is about one million rupees. The pollution control device, along with the chimney and associated structures, cost about a million and a half rupees.

Although the initial cost of a DBC is higher than that of a conventional cupola design, on account of better material and component specifications, its one-year payback period (on the basis of coke savings alone) makes the DBC a must for all foundry owners who want to stay in business for long. Freedom from all pollution woes, now and for the future, is a definite motivation to invest in a better pollution-control system technology.

Beneficiaries

It turned out to be a win-win situation for all involved – foundry owners, workers, and their families. The Indian Foundry Association nominated Bharat Engineering Works, Howrah, for setting up a demonstration plant. The coke savings in this foundry unit that manufactures ingot moulds was 35%. Additionally, there was an increase in metal tapping temperature and reduction in silicon and manganese losses.

To date, TERI has provided technical assistance to almost a dozen small-scale foundry units for replicating the DBC. Some of these units are located in major foundry clusters in Coimbatore, Howrah, Nagpur, Rajkot, and Vijayawada. These foundries produce a wide variety of castings like hand-pumps, centrifugal pumps, electric motor bodies; automobile components like flywheels; and sanitary items like C I pipes and manhole covers. TERI has also helped a foundry unit located in West Bengal in successfully averting closure by providing the design for a pollution-control system.