ENGINEERING: John Thompson's Unique Bag-Filter Solution
Recent Western Cape Business News
JOHN THOMPSON recently completed installation of a new coal fired steam boiler at Ladismith Cheese in the Southern Cape. What is unique about this plant is the fact that not only does it come with the latest control technology for efficient combustion of coal, but it also comes with a Bag-filter to reduce the particulate emissions to within European standards.
Bag-filters on smaller boilers of this size have thus far not been economically viable as the bags were subject to temperature constraints. By using glass bags with a PTFE membrane and ensuring the plant operates within the design parameters John Thompson were able develop a system which not only meet the requirements but also offers the durability demanded by industrial plant.
The steam installation comprises a John Thompson ‘Europac’ boiler producing 10000 kg/h of steam at 10bar with a particulate emission guaranteed at 50mg/m3 or less. The bag filter is in fact the final stage of gas cleaning with a mechanical cyclone grit arrestor maiking up the first stage. The gas burden at the cyclone arrestor outlet is approximately 300 mg/m3. The bulk of the ash is removed from inside the boiler via a submerged belt ash conveyor and smaller airborne grits are removed automatically in the reversal chamber where the air velocity drops before the final gas pass.
This boiler is fitted with the John Thompson micropac control system which, over and above the increased overall boiler efficiency, also offers the following advantages:
• Continuously optimized efficiency reducing fuel usage
• Coal Bed Management reduces smoke and particulate emissions
• Digital Air Distribution reducing Boiler Attendant Combustion Errors
• PLC - based optimum control strategy
• Inverters replace inherently inaccurate mechanical linkages
• Inverters reduce power consumption and noise levels under low load conditions
• Option for multi-loading boilers via local communication
• Superior response and turndown ratio
• Stoker protected by Electronic Torque Detection
• UPS ensures orderly shutdown during power outages.
Consider this; if the Micropac system and can improve a boiler efficiency by about 10% it means a coal saving of up to 2.5 tons per day or 75 tons per month which at R 500/ ton equates to R35 000 per month or roughly R 400 000 per annum. This however are only the direct fuel cost savings. By burning less fuel the emission levels are also reduced, as is electricity demand and fuel for transporting coal and ash to and from site.
With the resources available and the cost of fuel today one can accept the fact that coal is here to stay. With this in mind John Thompson has for the last number of years focussed its development programme on improved coal combustion and control which is now bearing fruit. With the addition of the new smaller size bag filter system to reduce particulate emissions the argument for coal as a fuel source for industrial boilers has just become stronger.
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