Reaching Heat Recovery Potential
Manufacturers looking to achieve maximum efficiencies from their steam system should consider the recovery of flash steam, and also look to detect and eliminate losses that are within their control
How to Reach Your Heat Recovery Potential
Key points:
• Before considering the recovery of flash steam, food and beverage manufacturers should take steps to detect any controllable steam loss.
• Ensure your steam and condensate loop is optimised by undertaking regular steam trap surveys conducted by experts.
• Certain food and beverage processes will inevitably result in flash steam plumes; these are unavoidable but create opportunities for energy recovery.
• When choosing a suitable heat sink for flash steam, location and synergy with the flash recovery process are important considerations for getting the best return on investment.
As discussed in previous blogs, there are two different types of steam plumes. One is caused by controllable losses, such as leaks from steam traps or safety valves, the other type is due to unavoidable losses, such as processes where the pressure change in the condensate leads to the presence of flash steam. In the latter case, this flash steam plume is recoverable.
Common causes of controllable losses
Controllable losses are commonly caused by steam traps. A steam trap is the interface between steam and the condensate side. The purpose of a steam trap is to discharge condensate while retaining live steam in the system. This ensures that the greatest amount of heat energy, the useful part of steam, is available at all times. Without condensate removal, you would struggle to achieve the processing temperatures and outputs you expect from your steam system– putting the safety of your product and the productivity of your system at risk! Good steam trap management results in a safer environment, greater operational efficiency and energy savings.
Regardless of the manufacturer, steam traps will occasionally fail, most often fail in an open position. This results in the leakage of steam and condensate. If a plant has tens or even hundreds of steam traps and a fail rate of 10%, a manufacturer will incur a considerable amount of undetected leakage over the course of a year. Factor in rising energy prices and manufacturers who do not survey their steam traps could be experiencing an increase in annual costs.
There are two different types of steam plumes. One is caused by controllable losses, such as leaks from steam traps or safety valves, the other type is due to unavoidable losses, such as processes where the pressure change in the condensate leads to the presence of flash steam.
Eliminating controllable losses
To assess and minimise controllable losses, regular surveys on the plant’s steam trap population should be conducted by an expert. This involves monitoring and recording the complete steam trap population, and clearly labelling each unit. An engineer will also inspect each steam trap to check that it is correctly installed and suitable for the application; they will also identify opportunities to optimise the steam and condensate loop.
A steam trap survey, conducted at least annually and, preferably, every six months, followed by a planned maintenance programme, is a good way to maximise energy efficiency and minimise process downtime. Bespoke steam system maintenance contracts to fit around your requirements are also available.
Recovering flash steam
Once any controllable losses have been eliminated, the manufacturer can consider opportunities for recovering flash steam. Processes where high temperatures are required often produce significant amounts of flash steam, when condensate is discharged through steam traps from a higher to a lower pressure. In food and beverage manufacturing plants, equipment and processes that generate flash steam include:
• Steam jacketed cooking vessels – these are often found in plants where soup or sauce is manufactured.
• Hot water generation – used by most food and beverage manufacturing sites as part of their hygiene procedures.
• Retorts and autoclaves – used for sterilisation in, for example, the manufacturer of tinned foods.
• Dryers – such as those used in meat-rendering processes.
Choosing a heat sink
When recovering flash steam, another challenge is to find a location or process where the recovered energy can be used– this is known as the heat sink. Ideally, the heat sink will be located as close to the flash steam plume as possible. For example, if the flash steam is located in the boiler house, a water system that needs pre-heating, such as the feed water for the boiler, would be a good option. It’s also important to consider the process connected with the heat sink, for example recovering flash steam around the clock for a process operating intermittently may not always be the best heat sink. A storage or buffer system, such as a hot water tank, is a possibility for optimising your steam system – it’s important to seek professional advice to assess the energy efficiencies that can be made.
Want to learn more about this topic? Listen to Episode 4 of the Talking Steam: Focus on Food
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