John Thompson, the Power division of ACTOM (Pty) Ltd., has been designing and manufacturing industrial boilers and associated plant at its head office and factory near Cape Town for over 60 years. The company’s latest development is a coal-fired hot water generator that is suitable for low temperature process heating applications. Named AquaGen, it comes complete with an efficient combustion system and flue-gas clean-up equipment that complies with the latest requirements of the Air Quality Act.
In some industries that need low temperature process heating – due to the heat load and distributed nature of production – electricity is not normally used as an energy source. Instead, either LPG (Liquid Petroleum Gas) or coal is used. However, LPG, like electricity, is an extremely expensive energy source and is often in short or interrupted supply. Also, the cost of LPG is in the order of R235/GJ (Gigajoule) whereas the cost of coal delivered to site is below R55/GJ.
Historically, some industries use coal-fired heaters, which are low-pressure “wagon type” designs referred to as "tobacco boilers." These heaters with underfeed stokers are inherently inefficient, unreliable and are usually not equipped with any form of flue-gas cleaning. While low in capital cost, the total cost of ownership of such equipment has proven to be rather high.
Design of the AquaGen hot water generator
After conducting an investigation to reduce energy costs and replace existing direct-fired LPG heaters for heating applications in the food and agriculture industries, John Thompson designed an alternative indirect heating system using a hot water generator. The solution that their engineers came up with incorporates a low-pressure, low mass, hot water generator with optimal material thicknesses and low manufacturing hours. Due to the low water temperature required by the process the generator is not classified as a pressure vessel or a boiler. As the working pressure of the generator is limited to 50kPa, costs normally associated with designs based on pressure vessel and boiler regulations do not apply.
The fundamental design, derived from John Thompson's highly successful Europac coal-fired steam boiler, is the same horizontal, three-pass, wet-back design for high efficiency and optimal fuel consumption. The combustion system is based on the well-proven Thompson Triumph chaingrate stoker with a control system incorporating a micro-controller for the air:fuel ratio and AC inverters on all motors for electrical energy savings.
In addition to coal, a wide variety of biomass fuels can be burnt on the chaingrate stoker including: wood pucks, wood chips, wood pellets, grape pomace pellets, nut shells, torrified biomass and sunflower husks.
The environmentally friendly and automatic AquaGen hot water generator is suitable for any industry that requires low temperature process heating. Generators with six heat output ratings from 1MW to 6.5MW are available, with a thermal efficiency of up to 88%, dependent upon customer requirements and coal quality.
Several AquaGens have already been manufactured and installed and are now generating hot water in the food industry with significant cost savings over the heating systems they replaced.