Monckton Coke and Chemicals at Royston in South Yorkshire has been producing coke for over 130 years and is the only independent coke production plant in the UK. Ranked as one of Europe’s leading producers of high-quality metallurgical coke Monckton produces some 200,000 tonnes of coke per year. The production process involves ‘baking’ coal in high-temperature ovens in the absence of air for about 20 hours.
During the baking process many of the by-products that come from coke making at Monckton are recycled and sold. One significant bye product of the process is gas which is taken off, cleaned up and split 50/50 for the purposes of fuelling the coke ovens for heating the coal and the CHP (combined Heat & Power) plant containing two steam boilers from which steam is passed through a steam turbine and on to a generator. This plant can generate up to 11 megawatts of electricity, sufficient not only for all the electricity needed on-site but also a surplus which is sold to the national grid.
In order for the plant to function efficiently and optimise production, the steam turbine requires a constant steam feed from the boilers. Operating at at optimum capacity means that both boilers need a continuous supply of clean water and it is here that the process is reliant on the constant availability of three Fabbrica horizontal multistage boiler feed pumps. Should there be a boiler feed pump failure, then the plant has to operate with just two boiler feed pumps leaving no cover should one of these also fail. One pump is insufficient to feed two boilers, so in such an eventuality one boiler has to be shut down and it has to flare off the excess gas that cannot be used.
The plant has been using the three Fabbrica pumps in a two–operational and one standby arrangement for over 15 years. The three Fabrica pumps operate at a pressure of 56 bar and deliver 30 tonnes of water per hour, which meets the boilers’ continuous production capacity of 30 tonnes per hour. The water being pumped is of a very high quality produced by the company’s on-site RO desalination plant. The company’s main concern is ensuring the quality of steam as this can destroy the turbine should it fall below the established quality level.
In order to keep these expensive pumps in good condition and extend their working life, the company’s in-house engineers operate a pro-active maintenance regime. However, even allowing for regular maintenance, problems can occur and back in 2010 a couple of incidents involved the performance of one pump dropping off. When the pump was opened up the impeller was found to be severely corroded, prompting the in-house maintenance team to call in pump repair and maintenance specialists AxFlow Huddersfield.
Having removed the pump from site to its facilities in Huddersfield (Fig.1) AxFlow completely stripped down the pump to identify the problems and recommend a re-engineering strategy. A further consideration that had to be factored into the repair programme was time, given that the coke plant could not be without the availability of three full-functioning pumps for an extended period.
“We identified severe erosion of the pump casing, pump housing and diffuser,” reports Tom Cooper, AxFlow Huddersfield Service Centre Manager. “Our solution was to rebuild the eroded pump parts by shot-blasting, lining the casings with stainless steel mesh and applying Belzona high temperature coatings,” continues Cooper. “The final job was to reassemble the pumps with new mechanical seals, bearings and ‘O’ rings and pressure-test the pump prior to re-installing the pump using laser alignment.” The job was completed in just seven days.
“They did an absolutely marvellous job on it and turned it around very quickly,” reports Mick Collins, Engineering Manager at Monckton Coke and Chemicals. So impressed was the company that when another Fabbrica pump required attention, AxFlow were recalled to the plant.
The summer of 2013 saw the Huddersfield team back on site to carry out repairs to the second of the pumps, which was suffering from corrosion and damage to three of the impellers. “This time around the work was more demanding,” says Tom Cooper. “Three impellers were damaged at the keyway, (this being only part of the keyway that had cracked), the bearing sleeve was slightly worn, the recirculation hole was badly corroded, the casings were badly eroded (Fig.2) and there was a 9” hole in the casing. As a result of this hole, the wear ring was rattling around on the impeller neck. And if that wasn’t enough, the shaft was slightly bent (0.010”) at the coupling end,” reports Tom Cooper.
AxFlow’s proposal was to tig-weld repair the impellers and keyway, rebuild the recirculation hole with Belzona, machine new casings, straighten the shaft to within 0.002” and replace the mechanical seals, bearings, oil seals and all ‘O’ rings. The final stage was to test the pump hydrostatically and re-install it at the Monckton plant. Once again, time was of the essence and AxFlow turned the job around in six days (Fig.3).
“We have enjoyed a long relationship with Monckton Coke and Chemicals and understand their reliance on having a full complement of pumps for all applications available at all times,” comments Tom Cooper. “Here in Huddersfield, we have the engineering resources to address the issues that they faced with the Fabbrica pumps, so we were able to provide a fast turnaround.”
For further product details, contact:
Tony Peters
AxFlow Ltd
Orion Park
Northfield Avenue
London W13 9SJ
Tel: 020 8579 2111
Email: info@axflow.co.uk
www.axflow.co.uk
