Many utility power plants are approaching the end of their design life, with engineers conducting life extension studies for boilers and related auxiliary equipment. In order to accommodate a changing operating environment, redesigning components and equipment to replace those which have reached the end of their useful life is increasingly common practice, says engineering, manufacturing, construction and maintenance service provider Steinmüller Africa.
Steinmüller Africa process engineer Keyur Patel says heat exchangers, which form part of the auxiliary equipment that heats the feed water entering the boiler, are vital components that need to be maintained to ensure optimal functioning of the power station. “If the temperature of the feed water going into the boiler is lower than the design condition, the overall efficiency of the plant will decrease.” Therefore, it is desirable to maintain the performance of high-pressure (HP) heaters and replace them when required to not only improve cycle efficiency but also prevent abnormal operating conditions for the boiler and thermal shock in the boiler thick-walled components.
Patel notes that the company started the HP heater design development process in 2009. The ongoing development initiative entailed training a team of engineers from the process, mechanical and drafting departments so that they can produce a high-quality design in a short time. The team comprises six technical specialists – two engineers each from the process and mechanical departments, and two 3D draughtsmen from the drafting department. The focus of development for the technical team was on specifying outcome requirements for the HP heaters, listing and familiarising themselves with the design codes to be used, generating process flow diagrams, allocating responsibilities to team members and closing information divides between departments.
The development initiative also included a long term skills transfer program from an experienced German engineer, who was previously involved in the design of the majority of the HP heaters currently in operation at 10 local power stations. Patel comments that an important aspect was to ensure that the design complemented Steinmüller Africa’s internal manufacturing capabilities without excessive additional capital expenditure. Consequently, the company, which is involved in the manufacture and maintenance of utility-scale pulverised coal steam generators, now offers turnkey solutions for header-type, tube sheet-type, shell and tube heat exchangers.
“The header-type heat exchanger consists essentially of two thick-walled headers inside a pressure vessel shell, distributing feed water through numerous ‘snake tubes’ connecting the two headers to absorb heat from the bled steam on the shell side of the heater,” explains Steinmüller Africa boiler process group leader Warwick Ham. He notes that the headers are very similar to those used in HP water-tube boilers, components in which the company has extensive experience. Further, Steinmüller Africa is also experienced in modelling dynamic heat and mass transfer, component sizing, mechanical design and vessel manufacturing.Ham notes that, based on the company’s current capabilities and its level of power sector exposure, it is a natural fit for Steinmüller Africa to provide the design, manufacturing and supply of the complete range of HP heaters and also low-pressure heaters in future.
Steinmüller Africa recently supplied five HP heaters of the tube sheet-type to Arnot Power station in Mpumalanga. Further, the company is also looking forward to receiving new work from the renewable-energy sector, especially concentrated solar plants (CSP). The CSP plants use the HP heat exchangers extensively to transfer the heat between the molten salt and the steam plant.
By: Nadine James, Reporter with contributions from Warwick Ham, Process Group Leader and Keyur Patel, Process Engineer