A synopsis on the reasons for incorporating an air blaster system to ensure material flow, describing the various facets of the installation and the results that were subsequently achieved on the Mill Feed Coal Bunkers and Reclaimed Coal Storage Hoppers on this 1000 mega watt Power Station situated on the River Severn at Ironbridge in Shropshire.

INTRODUCTION
Mill Feed Bunker
lronbridge Power Station produces a maximum 1000 mega watts from two 500 mega watt units. Each unit has 6 coal storage bunkers, 5 duty and 1 standby. The bunkers hold approximately 450 tons of coal each and are constructed from steel with glass tile linings. They measure 14.6m x 7.3m at the top with a depth of approximately 14.3m.

Reclaim Hoppers
Mobile plant recovers coal from the stocking out area and feeds it onto the conveying system via the Reclaim Hoppers, which are located adjacent to the rail coal unloading facility. Each hopper holds approximately 70 tons and measures 3.67m x 6.lm at the top by 6.lm deep. They are constructed from reinforced concrete with glass tile linings.

THE PROBLEMS
Efficiency in any industry has to be measured against the cost effective basis of its operation and nowhere is this more important than in the power generation sector where the responsibility lies for satisfying the ever increasing demand for continuous economic energy.

The cost of producing electricity could be reduced by burning low cost slurry, but the use of such slurry creates its own handling problem. lronbridge Power Station had accepted the need to find a method of overcoming this in order to help in their own efforts to improve efficiency.

The Station was burning a mixture of pit coal and slurry which was sticking in the Mill Feed Bunkers and reducing live capacity, generally as shown in D on opposite page. They had experienced so much loss of coal and capacity that on occasions it was necessary to operate a night shift for the express purpose of removing the material blockages and the increasing refill frequency.

The Reclaim Hoppers were also suffering the problem shown in D on opposite page, due to the high moisture content of the reclaimed stock coal, such that when on continuous reclaim during periods of the winter months, blockages were occurring every three to four hours and at times continuously with the attendant 'knock-out' effect leading to loss of output.

The need to intensify the use of the very fuels that were creating the loss of output, exposed the inefficiency of the existing situation and led to the Station's engineers studying the latest technological developments in material flow systems.

Approved by the C.E.G.B. for the installation of its Air Blaster Systems, which were enabling many other fossil fired power stations to maintain controlled coal flow, Linemann Halflo was approached by lronbridge regarding the problems.

THE SOLUTION
Mill Feed Bunkers
During 1982 a pilot installation of 8 GAB Series 4 Air Blasters was installed to Unit 1 C Bunker. This proved extremely successful to both operational and coal plant personnel. In 1983 a further contract was placed to install 2 GAB Series 4 Air Blasters on each of the remaining eleven bunkers, for a bridge breaking facility, although initially controlled locally, this was extended to give remote operation from the respective unit control desks within the Control Room.

Although this system proved invaluable it was acknowledged that the initial pilot installation also offered the potential of a trimming/bunker management capability, and in 1986 Linemann was awarded the total turn key contract to fully equip the Mill Feed Bunkers with Air Blasters.

Scope
A total of 8 Air Blasters are now strategically positioned on each of the 12 bunkers. They are operated manually using the push button control panels that are situated at the top levels of each bunker and by two modes of automatic control through an Alien Bradley mini programmable logic control system.

Normal Mode - firing Air Blasters in sequence to give controlled coal flow.

Trimming Mode - firing Air Blasters in rapid sequence to empty bunkers for maintenance or unit shut down.

Two A.P.E. Bellis BM30 Commander Series Compressors, (duty and standby, rated at 8.28m 3/M in at 7k g/CM2) together with control equipment and a 21.23m 3 Air Receiver, are installed within the Compressor House. Although dedicated for the Air Blaster System, the necessary pipework has been installed to facilitate connection to the existing Station supply system. A 150mm bus main also links the Compressor House with the Air Blaster System itself.

Safety Platforms provide access to all of the Air Blasters for ease of inspection and maintenance.

Reclaim Hoppers
Included within the same contract was a parallel system on the Reclaim Hoppers. Five GAB Series 3 Air Blasters are positioned on each of the three hoppers. A local control panel provides manual press button control over each individual Air Blaster together with automatic sequential control, preselectable for any of the hoppers. The facility was also included to link the system to the main coal plant control room, enabling remote initiation of the automatic sequence. Safety access platforms were again installed to allow for inspection and maintenance of all Air Blasters.

Both Air Blaster installations were designed and installed to C.E.G.B. STD 841701 Issue 2.

EVALUATION
Mill-Feed Bunkers
After a very short period the effectiveness of the installation

has been proven by the following factors:-

A) Fully utilising the automatic sequential control 24 hours a day has created a far superior coal management regime and restored usable 'live' capacity.

B) Prior to recently taking Unit 1 out of service for its planned outage, the Air Blaster System was used via its automatic trim mode capability to trim and empty the six coal bunkers for that unit, a task which has always been accepted as taking 72 hours with conventional air hoses, a high labour and especially high compressed air/energy factor. This task was reduced with the use of the Air Blaster system to 10 hours during one night shift without any of the previous flow problems.

Reclaim Hoppers
Linemann's ability to interpret the situation and to forecast the effects of different material characteristics, was proven conclusively after the Reclaim Hoppers proved extremely successful and met with universal approval from all coal plant operating staff. Over the Christmas/New Year period 1986/7, the Station operated exclusively on coal reclaimed from stock, a period of 12 days in which the Air Blasters prevented a single blockage from occurring and made it unnecessary to use air lances to trim the Reclaim Hoppers.

CONCLUSIONS
The results presented in the previous section indicate the significant improvements achieved with the two Air Blaster Systems. Costing over £400,000 the installation was the largest contract for Air Blasters ever recorded in the United Kingdom, and one which will save lronbridge Power Station in excess of £750,000 every year on fuel costs.

Linemann Halflo's expertise has provided an extremely cost effective method of improving efficiency within an impressively short pay back period.

IMAGES

		Air Blasters & Safety Access platforms to coal Mill Feed Hoppers			Flow problems
		Air Blasters & Safety Access platforms to coal Reclaim Hoppers			Control centre for Air Blasters on Mill Feed Hoppers
		Air Compressors & Receiver			Air Blasters installed on Reclaim Hopper constructed of reinforced concrete