Project LA – Cast shop flue gas treatment

The two Cast Shop holding furnaces needed to have a flue gas treatment plant to abate the emissions from emitting to the atmosphere.

As the furnaces are only operational one at a time, we needed to design two duct runs one for each furnace with automated valves to the filter.

The client then specified that we needed another extraction point from the Alphur de-gasser stack which would also need to be filtered.

Within this project Filter Designs was responsible for the design, fabrication, installation, and commissioning of the filter system. At the beginning of the project there was quite a lot of back and forth regarding the requirements needed to ensure the filter system would work.

After working in partnership with our client along with site visits FDL gathered all information needed to figure out the correct specification for the filter system needed. Most of the filter was pre-assembled at the fabrication site to save time on site, also so the lift from the delivery lorry to the assembled support structure would be a straight and easy lift.

As site is in Scotland, we were able to use a local fabrication company who were familiar with the site, to fabricate the ducting and staircase and carry out the installation to allow us to save the client some money. 

Filter Details:

• cleanPULSE Reverse Jet Filter 

• Filter arrangement 10 rows of 10 bags    

• Ø127mm diameter x 3000mm 

• Filtration gas volume 4,877Am3/hr 

The filter itself is a reverse jet cleanPULSE filter designed specifically for the requirements in house using our 3D Inventor capabilities. The filter has 100 vertically hanging bags and a pulse cleaning tank to ‘pulse down’ the bags based on differential pressure.

The filter was also insulated and clad. We also installed 4x 240V 1000W trace heating pads on the hoppers of the filters to limit the possibility of condensation when not in use.

Project Summary

The equipment broadly comprises ducting, a drop out/spark arrest box, high temperature butterfly valves (spring return), modulating air bleed valve a bag filter, bulk bag bicarb skid, outlet ducting complete with isokinetic sampling points and a dust monitor, two fans (duty standby) with manual damper and chimney with motors, instruments, and switches through a control panel.

The furnace outlet temperature is around 850° and the filter inlet temperature has been designed for 200°c. We used a heat calculator to determine the heat loss over the ducting to ensure 200°c at the filter. We also installed a failsafe air bleed just after the spark box which will open to modulate the filter inlet temperature to 200°c.

The ducting run from each furnace has a pressure transmitter which is modulated by the fans (duty / standby) to maintain a setpoint pressure in the furnace outlet. Each duct run is controlled via the control panel which has a furnace selector key switch to allow the user to choose which furnace is extracted from.

cleanSPARK arrester box

The spark detection box has baffles and a perforated sheet to stop any debris, which may still be alight from the furnace getting to the filter and risking a potential bag fire.  The spark arrest box has a hopper with an access door, a manual slide valve and a collection bin.

cleanDOSE Sorbent Skid

Whenever the abatement of acid gases is required, we first seek out the gas composition data from our client. Based on this, we can now advise with reasonable accuracy what the likely reagent consumption is going to be. This assists with CAPEX and OPEX planning. Information on SOx, NOx and HCl levels will allow us to determine the use of Lime or Sodium Bicarbonate. This will also direct our specification of equipment.

Controls

The control system on any emissions control plant is an important aspect of the project. When the Environment Agency calls for shut down of a non-emissions compliant plant after 4 hours outside of the emissions limits, the control system needs to be robust and reliable.

At Filter Designs we take this seriously and have several control panel builders who specialise in bespoke systems. To communicate our requirements, Filter Designs compile a series of documents including functional design specification, process and instrument drawings, electrical lists, layout drawings, P&ID’s and more. We also integrate where possible any air management, so that various regulators and solenoids are protected in a control’s enclosure.

Factory acceptance testing can be completed in a variety of ways, but the acid test is simulation of the various inputs and outputs and confirming the control systems response to these.

Having commissioned several systems in the UK and abroad in temperatures ranging from -20°C to +40°C, we appreciate that all the workshop-based testing which can be done, should be done to ensure the most efficient use time on site.

Typically, this begins with point-to-point testing of the electrical cabling, then running up motors and instruments with functionality testing, followed by sequencing the control code to check the order of start-up, shut-down and critical orders.

In all projects which accept remote access, we actively promote the use of it. This allows us to advise on the efficiencies of plant running and we can respond and advise on any alarms which can occur on a waste to energy plant of this size and complexity.

Report by Darren Jones - Filter Designs Ltd - March 2021