Using Technology to Reduce Energy Bills
Published on : Sunday 02-05-2021
Vipul Parikh presents a case study of adoption of new technology to reduce energy bills.
In any typical chemical manufacturing company (be it a Pharma, Agro-chemicals, Speciality chemicals and dye manufacturing units), almost 60% cost of power and fuel is consumed in utilities, i.e., cooling water, chilled water, brine plant, boiler, air compressor, nitrogen plant, etc.
As we all know energy is neither created nor destroyed and every unit of energy saved is energy generated. So to be competitive and to reduce the operating cost, energy saving is a must. It will also lead to reduction in greenhouse gases generation, which is responsible for global warming.
As I have vast experience, nearly three decades in various chemical industries, I got an opportunity to have exposure to different techniques and technologies to reduce energy bills.
Presented in the following paragraphs is a case of adoption of new technology to reduce energy bills.
Problem
The chilled water plant having a capacity of 150 TR is having conventional shell and tube type condenser. As the condenser was getting choked over a period, it resulted in poor heat transfer with low COP (coefficient of performance), which necessitated regular cleaning of tubes to maintain the efficiency of the machine.
Chilled water plant capacity: 150 TR.
Existing condenser configuration: Shell and tube type.
Proposed condenser: Mixed flow evaporative type.
Solution
To eliminate the problem and to maintain the efficiency, an evaporative condenser with SS304 tubes has been installed in place of a shell and tube type condenser.
Being a dedicated chilled water plant for new production blocks, power consumption per MT of product evaluated for two months before changing the condenser and two months after changing the condenser.
The specific power consumption of the chilled water compressor per MT of production was 104.6 kWh/MT before changing the condenser.
The same came down to 82.1 kWh/MT after installing an evaporative condenser.
Reduction in power consumption in units: 22.5 kWh/MT
Saving achieved due to the Evaporative Condenser: Rs 11.13 lakh/annum @ 500 MT/month production rate.
Investment is Rs 12.5 lakh: Simple payback in 1.1 year...!
The water quality should be potable water as a make-up in evaporative condensers. Evaporative condenser sump volume is hardly 1-2 kL so it is very easy to clean the sump in a few hours. Even we can over design the surface area required for evaporative condensers by 10% to get the lower condensing temperature just by adding only 50-60K to the capital cost.
Another advantage here is saving in cooling water pumping cost required for shell and tube type heat exchanger vs evaporative condenser. The net impact in additional power cost saving is 7.5 kW/hr.
Advantages of mixed flow evaporative condenser
An evaporative condenser replaces the intermediate heat exchanger, secondary pump piping and cooling tower into a single unit.
In a mixed flow evaporative condenser, heat transfer is divided into Coil & Fills.
Also, in this combined flow machine, 500-600 TDS water can be used.
The design is done in such a way that a major portion (75-80%) of evaporation takes place on the fills and only partial evaporation happens on the coil, thus reducing the scaling and fouling over the coil. For fills cleaning, access door and walkway grating is provided. Also, ladder, handrail and walkway grating at top has been provided for fan-motor and nozzle maintenance. Hence, online maintenance is easily possible, no need to shut down the unit.
As the scaling only happens on fills, the coil remains safe. The life of fills is 3-5 years (depending upon water quality) and can be easily replaced. Also, cost of fills is very minimal in comparison to the cost of SS304 coil.
The parallel flow between air and water on the coils also helps in uniform spray water coverage over the tubes. This further helps in efficient heat transfer and also reduces dry spots at the tube bottom which normally accelerate scaling and corrosion process.
This is one of the processes, there are many more technologies available to reduce your power bill.
Vipul Parikh is a Mechanical Engineer, having total experience of 28 years in chemical process industries. He started his career with Tata Chemicals and has since worked with other reputed companies like Atul Limited, Lupin Limited, Sun Pharma, Aurobindo Pharma and many more. Parikh is presently working with Transpek Industry Ltd, as a General Manager – Engineering services. During the journey, he has got exposure to many technologies and techniques to conserve energy. Comments welcome on email: [email protected]
