Commercial director of Associated Energy Services (AES), Dennis Williams says that strong partnerships with thermal energy users optimise opportunities to benefit from condensate return (CR), waste heat recovery, and the prevention of system contamination. Steam quality is the responsibility of AES on the sites it manages, and this includes protecting the boiler assets and the quality of steam supply to ensure optimised plant and boiler operations.
The client must manage the collection and return of condensate because this is integral to the use of steam, and should be controlled by production personnel as it impacts on plant operation. The client’s steam usage system determines both the quality and amount of condensate available. If steam is used via direct injection, no condensate can be recovered. If steam is an indirect heat source (in coils or heating jackets), then condensate can be extracted.
Williams explains that key factors such as conductivity, hardness and temperature all determine quality. Total dissolved solids (TDS) and hardness stem from the contamination of steam or condensate circuits in the client’s facility, such as leaking heat exchangers or coils. This results in product ingress into the circuit. It can also come from heating and cooling plenums, where there is no rinse cycle after the cooling cycle. Condensate is then contaminated with cooling water that is high in TDS and hardness. The higher return rates of hot, high-quality condensate assist in optimising steam generation as follows:
• All sensible heat returned saves on fuel inputs.
• The higher percentage of CR requires less make-up water to account for the CR losses, and the use of less fuel to heat the make-up water from ambient temperature to boiler steam temperature.
• A higher percentage of CR also means lower TDS compared to make-up water, and therefore less blow-down to maintain boiler TDS, less fuel input energy, less water costs and less water treatment.
However, if TDS is out of specification, the condensate cannot be used and must be dumped, as it will foul the boiler heat exchange surfaces, cause higher fuel usage and potentially damage the boiler pressure part.
Partnering with clients to optimise condensate return
AES works closely with clients to optimise CR systems. “One of our clients in the food sector had no fundamental technical understanding of the heat exchange systems within its facility, and could not determine the percentage condensate return that could be achieved,” says Williams. “Solo and third-party assisted tours of the plant provided technical guidance and isolated sections to determine condensate return flows, revealing potential condensate contamination. Several process units were identified to be addressed by the client.”
Economics of condensate return
At another industrial manufacturing site, AES identified process issues in heating and cooling cycles resulting in high TDS and hardness in the CR returned, making it unusable at the boiler house. “We proposed a control system designed to allow for a post-cooling cycle flush. This will ensure that high TDS and hardness is flushed before steam is introduced, thereby ensuring clean CR. The expected savings are approximately R6000 per month for every 1% improvement in the CR to the hotwell. With a potential upper limit of 80%, significant savings can be achieve,” explains Williams.
He recommends analysing where and how energy is used and identifying the best-matched applications. Where energy benefits are low, lower grade energy uses such as cleaning water should be substituted. By using the recovered low temperature CR, less water is needed to heat the cleaning water.
‘Return’ solutions
He observes that while some challenges are transitory, others can be severe and costly, such as introducing contaminated or high TDS CR into the boiler steam system. If left unattended, this causes boiler fouling and plant failure. Contamination can lead to boiler control issues such as fluctuating water levels and boiler trips, and even carry-over of water slugs into the steam range with the potential for water hammer and line damage.
The solution is proper design, layout and planning of condensate recovery systems. Designs differ between plants, for example, a high-speed paper machine versus a heating coil on a cooker vessel. Regular maintenance of heat exchange equipment and testing of both CR and product for signs of leaks between the steam and product spaces is also critical. AES prioritises preventing system deterioration and managing feedwater chemistry.
“Clear and timeous communication between AES and our clients is critical in managing expectations and in achieving the best results. It is a partnership,” Williams concludes.
For more information contact AES,
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