Sulphur Dioxide (SO2) emissions cause particular problems to any modern power generator, but can easily be reduced by the addition of sorbent materials into the combustion process.
Crushed Limestone is injected continuously, directly into the bed of the boiler along with the coal. Air is then forced into the combustor from the bottom inducing a pressure, which floats the limestone and coal within the combustion chamber allowing it to behave like a fluid. This provides certain combustion benefits, including reduced formation of Nitrogen Oxides (NOx). In addition, the limestone chemically absorbs Sulphur Dioxide (SO2) directly from the gases in the boiler, reducing (SO2) emissions. Gypsum is formed as a result of this desulphurisation process and is discharged with the bed ash and fly ash. Particulate matter suspended in the flue gas, as well as fine particulates of limestone, are then captured by a fabric filter or electrostatic precipitator (ESP).
Sand Injection Technology
Silica Sand is generally used as the base bed material for fluid bed combustion. It is usually only used on boiler initial start-up and once stable operating conditions are achieved the bed is replenished using the coarser bed ash which is recycled, or the sorbent, added for desulphurisation reasons. Most grades of sand can be easily handled in bulk form with dense-phase pneumatic conveying, in fact Foundry Sand, used for moulding, was the first material ever conveyed through the DensPhase system and there have been numerous successful installations in that industry since the mid 1970’s. If the sand is required to be continuously injected, then Clyde Bergemann DoncasterRotofeed® technology would be suitable.
Waste Derived Fuel Injection Technology
Clyde Bergemann Doncaster has successfully commissioned an important contract from Scottish Power Generation Limited for the provision of a Waste Derived Fuel (WDF) storage and transportation
WDF is a dry, biologically benign and virtually odourless granule made from sewage sludge and although of a lower calorific value than coal, it can represent a useful and valuable fuel. The benefits of processing this otherwise waste material into a renewable energy source cannot be overstated since the ban on dumping at sea and the cost and environmental concerns associated with landfill disposal.
In terms of a handling system for this material, two major factors had to be overcome. The system needed to be totally enclosed and it had to be capable of dosing (and monitoring) measured amounts of material into the process.
The answer was a new transportation system from Clyde Bergemann Doncaster, using the company's well-proven Rotofeed® Injection Technology. The WDF is transported from the customer's road tankers into six new storage silos and from here, two Clyde Bergemann DoncasterMulti-Outlet Rotofeeds® continuously inject metered amounts of Waste Derived Fuel (WDF) material along 400 metre long pipe into the coal feeders at the coal mills where it is mixed with the coal and pulverised prior to be co-fired into two 600MWe boilers.
Clyde Bergemann Doncaster originally developed the Rotofeed® System for injecting granular coal into blast furnaces. It's dual advantages of keeping the material totally enclosed whilst allowing very accurate feed rates makes it ideally suited to handling WDF.
