Boiler reconditioner and manufacturer Dryden Combustion launched its new Mk7 coal-fired boiler in South Africa this month.

Two of these boilers will be installed in the Cape later this year.

“The new Dryden Mk7 coal-fired boiler is a welcome alternative to an industry that has had limited options to date,” says Dryden Combustion MD Gordon Slater.

He claims that, for more than 20 years, there has been only one main supplier of coal-fired boilers in South Africa and that the Dryden Mk7 will create competition in the market.

The boiler has outputs ranging from 1 000 kg/h to 21 000 kg/h and features operating pressures of up to 2 000 kPa.

“The Dryden Mk7 comprises a fully wetback range of coal-fired boilers. It is a modern, efficient unit, with a three-pass shell-boiler design, coal-fired with a fully water-cooled combustion chamber. The twin-flue boilers have separate walker-type combustion chambers, allowing single flue firing.

“A variety of models are available and manufactured under the supervision of an approved third-party inspection authority,” Slater says.

The Dryden Mk7 has a specially developed, high-efficiency low-power induced draught fan, with curved and radially tipped blades for minimum fly-ash build-up.

“The fan and impeller are statically and dynamically balanced for smooth operation in service.

“The boiler output is affected by the change in the calorific value of the fuel. The burning of fibrous fuels can also be accommodated,” says Dryden Combustion director Sue Kiley.

She explains that the Dryden Mk7 is fitted with a chaingrate stoker, with wide links for improved combustion performance.

“As it is one of the hardest worked components of any shell boiler, the stoker has a rugged design. Combustion air is provided by balanced draught equipment, which can be controlled by either a single-lever control unit or as an optional extra through a solid state-type electronic controller.

“These devices correctly adjust the induced draught dampers, forced draught damper and stoker motor speed for the most efficient combustion conditions.
“Efficiencies at full-rated capacity of up to 79% are attainable, with washed pea coal having a gross calorific value of 27 500 kJ/kg,” Kiley says.

She further explains that soot-blowing equipment is fitted as a standard feature to lengthen the intervals between tube cleaning and extend boiler activity in service.
“Direct coupled twin multistage boiler feed pumps are mounted on the boiler subframe, ensuring 100% standby for boiler feedwater.

“The control panel contains all the associa- ted electrical equipment and can be mounted on the boiler subframe, in accordance with the packaged boiler concept,” Kiley notes.

“We also offer the latest available technology for new boiler control systems, optimising combustion efficiency, saving energy and reducing air and noise pollution,” Slater adds.

Dryden Combustion was recently appointed as a partner and South African marketer and distributor of Bosch Thermotechnology.

“Bosch Thermotechnology manufactures more than 1 500 boilers a year. We have already received an order for a 20 000 kg/h, 30 bar gas-fired Bosch boiler, fitted with Hamworthy low-nitrogen-oxide, high- efficiency burners. The boiler will be delivered later this year,” Slater states.

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