Managing Dynamic Steam Plant Operation on a Multi-User Site

 In an ideal world, a single steam user has consistent load demand and operates continuously.  However, reality is rarely this simple – and managing a dynamic steam plant operation featuring multiple users requires strong technical skills, good communication and close attention to optimise results, explains AES Commercial Director, Dennis Williams.

Variations, including time and duration of use, steam draw profiles (either constant or batch, intermittent, staged), different steam pressure requirements, direct or indirect steam use and condensate return differences impact on operations – especially when it comes to training steam plant operators, different boiler technologies and fuels, and managing consistent steam pressure supply – all while factoring in the potential use of accumulators and steam pressure control valves.

Optimising efficiency of steam generation (boiler load balancing, fuel trims, emission management due to load changes), together with carefully managing changes to steam and condensate return reticulation systems (including startup / shutdown of lines / production from one or multiple steam users), specific water treatment requirements due to variations in direct / indirect steam use and the impact of reduced condensate return from steam users are also important additional factors.

Measuring and monitoring

“AES’s Remote Monitoring System (RMS) gathers steam generation plant data and records critical operational monitoring parameters including steam pressure (per boiler and header pressure), steam flow (total), steam loads per boiler, flue gas CO₂ per boiler, stack temperature per boiler, overall feedwater temperature and quality, and other operational impactors. This data is essential to monitor boiler efficiency and steam quality,” Williams points out.

“Other critical measurements at reticulation and usage points include steam pressure, steam pressure control systems (let-down stations etc.), the condensate recovery system, particularly in terms of quality of condensate such as pH, total dissolved solids (TDS) and hardness or potential contamination through product leakage into the steam or condensate space),” he says.

The focus is not only on minimizing steam use to achieve energy requirements, but also on maximizing the percentage and quality of condensate return to save water and recover heat.

Process understanding and operational map

Understanding the process comes first when setting out to achieve efficient, optimal steam generation and thermal energy supply across a multi-use site, Williams notes: “This is critical in order to determine the energy flows required in terms of timing, tonnages, pressures, variability profiles and condensate return generated. These factors form an overall operational ‘map’ of the variation in demand and load on the steam plant.

”AES then determines the best operational strategy including when to start which assets, specific boilers’ load profiles at specific times, and the management of risk in the event of equipment challenges or breakdowns. Site-specific operating procedures (SSOPs) are optimised based on the configuration of the plant and user requirements. “

Throughout, says Williams, communication is key – particularly when it comes to setting realistic client expectations: “With AES’s hyper-focus on steam generation, there are fewer opportunities to point fingers. The boiler house has historically been blamed for many process disruptions. The data required to understand the root causes of issues was not always accessible. Fortunately, AES’s service level agreements (SLA) provide clear, measurable deliverables.”

Multi-use with multiple boilers

Williams acknowledges that it is far more complex to operate a multi-use site with multiple (duty) boilers, than with a single boiler: “Myriad factors under the control of the steam plant operator (AES) and the steam user (the client) must be coordinated. A single user site – while having the same operational requirements and levers – is inherently simpler. The demand input is less intensive – with lower impact around any potential operational issues on the generation plant.”

Additionally, pivotal Process Safety Management (PSM) within a multi-user environment requires consistent practices across multiple boilers: “We must ensure safe operation for multiple boiler plant (pressure vessels), multiple combustion devices operating, more hot surfaces, more maintenance (at heights and/or in enclosed spaces) and variations thereof if using different boiler designs, fuels or combustion systems. Therefore, a strong management system regarding permissions, task planning, risk review and procedure set-up is essential.”

On multi-user sites, there is also greater variability when it comes to pipework, valves, systems and operating procedures: “Start-up and shut-down of steam and condensate lines to particular units which are being brought into an out-of-service must be safely managed.

This includes heating of lines, condensate removal to prevent steam line water hammer as well as system lock-out to prevent steam burns and pressure release risks when restarting systems. Processes with different steam pressure requirements must be operated and maintained. Over-pressurisation of steam use systems downstream can have significant safety impacts,” Williams explains.

“Multi-user sites are challenging, demonstrating that crystal-clear communications and tried-and-tested technical skills and experience are imperative to ensure the successful integration of steam generation, reticulation and use,” he concludes.