Project ML2 – Fabric Filter Upgrade

We were asked to visit site to investigate upgrading the reverse jet pulse cleaning system for the existing fabric filter which serves the furnace. We informed the site that whilst we think that this will help with the high dP and pulse cleaning of the bags we feel that this isn’t the permanent solution to fix the issue. We issued a quote replace the current fabric filter with a new fully ‘’offline cleaning filter’’ the permanent solution to remove the need to shut down for 15 minutes per day.

The fabric filter top sections had been modified back in 2023 where the bag length had been reduced from 6.5m to 4.26m and the pulse tanks have been changed to 8’’ tanks with 1.5’’ double diaphragm valves.

As the tanks were struggling to pulse clean the bags causing high dP the operators had turned up the compressed air from 4 bar (FD standard) to 7 bar.

The issue with this is:

1. Bags will degrade quicker due to excessive compressed air pressure
2. Causes an adverse effect as the dust is known to be fine and potential for re-entrainment (this is where the dust is pulsed off the bags then immediately sucked back onto the bags)

Prior to installing our new reverse jet pulsing system and to counter the second issue above as a precaution site were backing off the furnace to allow the filter to pulse clean down with less gas flow. This was taking approximately 15mins every 24 hours and was accounting for £1.5 million in lost revenue per year.

The current set up before our changes were:

8’’ tanks which have an air volume of approx. 43.30 litres (compressed). With each pulse shot consuming 169,90 litres (uncompressed).

We felt that the pulse tanks and pulse valves were undersized for this application and as an example we used the filter we installed on the same site back in 2023 Partial Offline cleaning Filter which had 8’’ tanks with 1.5’’ double diaphragm valves and each pulse valve only needs to clean a surface area of 14.67m² rather than the 24.75m² on this filter.

We therefore decided to increase the tanks from 8’’ to 10’’ and making the valves 2’’ will give and increased tank volume of 69,90 litres (compressed) and pulse shot of 275,60 litres (uncompressed).

Originally the modified top section had 2 8’’ pulse tanks per filter section (3) which meant 6 tanks in total.

As we increased the pulse tanks from 8’’ to 10’’ and the valves from 1.5’’ to 2’’ we could only fit 1 16-way tank in place rather than the (2) 8-way tanks.

The original cages were split due to the length and had an internal venturi which was causing a build up on the top 150mm of the bags causing high dP. We took a spare filter cage top and designed a cage to match but with our external venturi fitted to allow better cleaning. The new pulse tanks were to be fitted in the same place as the original tanks to allow us to re-connect to the existing compressed air pipe work and electrics (solenoids). This meant designing new support plates for the tanks and jet tubes along with pipe spools with unions. The old tanks were mounted on plates which needed cutting out to facilitate our new mounting plates with connecting spools.

The new 2’’ jet tubes were fitted with nozzles which improve pulse cleaning of the bags.

The installation was planned to take 10 days for 3 men. Due to circumstances out of our control we had to complete the installation in 6 days! This meant our installation team had to put longer hours to get the install completed before the site wanted to start back up, not to mention the 30+ degree heat up on top of the filter!

We set up a plan to complete all the hot works and complete a section at a time so that the client’s night shift team could install the bags and cages prior to us starting the next section which would alleviate the pressure on us.

As the new tanks were extremely large and very heavy, we need to use skates to get these into the building and use the overhead maintenance crane to lift this up onto the filter.

We had pre-arranged a scaffold to be placed above where the tanks were to be fitted to allow us to lift using chain blocks to safely into postion.

Photos of the completed installation: