Dargavel update from SEPA, 30 March 2011

From March 2010 until March 2011 there have been 37 activations of the bypass stack. In the main these activations were related to high temperature trips and boiler fouling issues. SEPA and the Operator have prioritised work in this area and put in place the following changes to improve the situation:

the high temperature trigger point (which activates the bypass system in order to protect the bag filtration system) has been re-set; 
control programming have been amended to allow additional cooling air to be called upon (if available); 
if additional cooling air is not available then the control programming has been amended to automatically reduce the load on the secondary combustion chambers (i.e. reduce the production rate of syngas in the primary gasification chambers) and thereby bring the SCC exit temperatures down closer to their target limits (currently 1100°C for hazardous waste); 
a new operating procedure has been implemented to initiate a controlled shut-down of the gasification chambers before the main process fans reach maximum duty and trip out (thereby activating the bypass system). New boilers are proposed to resolve boiler tube fouling issues – this should significantly reduce the pressure drops across the boilers and lead to improved system control (i.e. less bypass activations); and finally 
power surge protection has been reviewed and increased to critical plant and control systems (power surges have previously resulted in bypass stack activation). 


There have been no bypass stack activations in the last two months.

For information, the plant at Dumfries is due to close shortly to facilitate the installation and commissioning of re-designed boilers. The facility will therefore be off-line for ~4months and the Operator expects the new boilers to produce a step-change in performance / reliability. This will allow the generation of superheated steam which will feed the turbine and generate power.