Resource detail

Background: Tata Steel was established in 1907 and has grown to become Asia’s first and India’s largest integrated private sector steel company. The Power House-3 or PH3, constructed before 1950 is the oldest unit at Steel Work and it provides for a major chunk of power requirement of the facility (approx. 30-45 MW). It comprises of the following units:

♦ Four coal fired spreader stoker boilers (boiler numbers 5, 6, 7 and 8) with steam generating capacity of 67.5 TPH (tonnes per hour) each at 485⁰C temperature and 63 bar (g) pressure.

♦ Two condensing steam turbine generators of 30 MW capacities each.

♦ Coal handling, ash handling and other auxiliary facilities.

Challenges: Burning of fossil fuel for power generation led to pollution, was a costly and unsustainable practice in the long run and led to a lot of wastage of useful energy that used to dissipate in the atmosphere.

♦ The fossil fuel used, Middling coal, caused emission of 4,50,000 tonnes of CO2 per annum apart from release of other pollutants like dust (48kg/h), SOx (oxides of sulphur; 242kg/h) and fly ash and bottom ash (2,13,000 tonnes per annum).

♦ The steel plant generated various waste products like BFG (blast furnace gas), COG (coke oven gas) and BOFG (basic oxygen furnace gas) from its operating units. While a part of these gasses was used in the steel plant, most was being splayed into the atmosphere after cleansing due to which the useful heat content of these gasses was being lost.

Thus the challenges that lay before Tata Steel were multifold.A proper heat balance was to be achieved while converting the stoker type coal fired boilers into gas fired boilers. The transition to new technology was not to be, in any way, detrimental to the output of the power plant.Secondly, while this conversion process was going on, the company had to meet the power requirements of the Steel Works as well as carry out effective management of the steam. Lastly, the waste gasses had to be transported to PH-3 that was located more than 2km away from the gas generating source, at required pressure.

Initiative: To prevent the wastage of useful heat of these by-gases, it was proposed that the thermal energy from these gases be utilized to generate power for the plant by first generating steam from that heat and subsequently producing electricity. To achieve this goal, all existing coal fired boilers of the PH-3 had to be converted to 100% waste gas fired boilers.

Thus major modifications were carried out in the boilers of the PH-3 in order to make the plant more efficient and waste as little energy and resources as possible. Technologically advanced tri-fuel scroll burners were installed in the boilers, capable of firing leans gases like BFG and BOFG, richer gas like COG as a support fuel and LDO (light diesel oil) as a secondary fuel. Also, the surface area of the boiler was enhanced so as to provide a larger area for transfer of heat from the waste gases by means of convection. Unwanted infrastructure like panels related to stroker drives, feeders, coal handling, ash handling systems and ESPs were dismantled and a distributed control system was introduced with engineering station, human machine interfaces, servers, upgraded instrumentation, control platform and a suitable combustion control system.

The no. of tubes was increased to increase the surface area, front walls and super heaters were modified, boiler tank tube in the flue was replaced and additional air pre heaters were provided. The conversion was done systematically in stages with application of critical chain project management tools for efficiently implementing the project.

A control philosophy was developed for supplying gas at higher pressure so that it is available at the right pressure at the boilers and lastly more than 2 km long overhead DN2400 gas pipeline was laid for transporting gases.

Outcome/Benefits: The aim was thus achieved by conversion of all existing coal fired boilers of PH-3 to 100% waste gas fired boilers. The carbon footprint was reduced dramatically and emission of all pollutants reduced significantly.

While consumption of coal, bottom ash and fly ash has reduced to an absolute 0 from 4,56,700; 1,31,500 and 81,800 tonnes per annum; the reduction in consumption of CO2, Dust and oxides of sulphur has also been drastic from 4,50,000 to 54,236TPA; 48 to 17kg/h and 242 to 97kg/h respectively. The boiler efficiency has also increased over the years from 79% in 2003 to 88% in 2008.

Commercially tested: Yes