Project THPL – Urea Prill Skid for DeNOx. Sodium Bicarbonate Dosing for DeSOx. Primary, Secondary and Tertiary Combustion Air System.

Waste Wood CHP plant

In 2011 the project involved providing a flue gas treatment plant for a biomass incinerator on the outskirts of Bedford. Intended to handle 30,000 tonnes of waste wood per year.

At that time Filter Designs installed the bag filter plus ducting, a 50m³ silo for Sodium Bi-carbonate, 2 x 160kW ID fans capable and 2 sound attenuators and culminating in an 18m tall stack with a platform and CEMS points, a bag tipping hopper for powdered Activated Carbon, another 50m³ silo for filter dust discharge feeding out via an inclined screw conveyors and culminating in a slewing ring mounted tubular screw dispensing into a tanker via telescopic bellows.

Sadly, before completion the project was mothballed as the main contractors went into receivership.

FDL worked behind the scenes, along with others for several years to help investors bring the project back to life with new operators until finally in 2014, the project was resurrected.

On this occasion Filter Designs added a Urea skid which allows the customer to buy in 0.5m³ bulk bags of dry urea Prill and mix with water on site before injecting via lances in the combustor.

By buying Urea in Prill form, the end user avoids paying the high costs involved in transporting large quantities of a high percentage water based solution. The skid has its own control panel with a HMI for changing parameters and set points, password protected of course!

The dosing rate is varied by inverter driven pumps and directly linked to the NOx signal from the CEMS system.

FDL also provided and installed a compressed air system which consisted of a pair of 22kw belt driven compressors to give duty and standby security.

The compressors run through an air receiver, fridge dryer and for the CEMS and some actuators on the plant requiring instrument quality air a further desiccant drier is incorporated.

The compressed air pipework we installed is a combination of aluminium ‘infinity’ 32 and 25mm diameter with localised flexible PTFE pipework suited to the higher temperatures we have experienced on similar plants.

The majority of the new work on site involved designing, manufacturing and installing 3 runs of ducting to carry re-circulation gases back to the combustor via a fail closed damper and fan as well as primary and secondary air ducting and fans.

All 3 systems incorporated a large up and over section to allow forklift access to other areas of the site and a number of hand operated butterfly valves and slide gate dampers.

Due to changes made elsewhere in the plant we have subsequently retrofitted fail open springs to the filter inlet damper Kinetrol actuators.

The economiser to filter ducting was modified also due to a change of economiser requiring us to alter the connecting ducting, re-using as much of the existing as possible.

The plant was commissioned in August/September of 2015 and is due to go into full operation before the end of 2015.

Designer: Simon Callis

Project Manager: Simon Callis/Stewart Callis