Process Equipment Update
detrimental effect on steam production and efficient power generation in the case of combined heat and power plant. However, there is a solution to this problem that not only removes the effect of transient steam loading completely from the steam raising or power plant but also improves energy efficiency and reduces operating costs. It is the incorporation of a ‘steam accumulator’ into the steam supply system.
Steam accumulation is a long established but too often forgotten technology that, if correctly applied, can continue to be of great benefit to enhancing the design and performance of steam plant and cogeneration in the modern boilerhouse.
Imagine a boiler able to reach a ‘peak’ demand 10 times higher than its rated output. Consider that two out of a bank of three boilers might be eliminated and still allow the remaining boiler to reach the same ‘peak’. Contemplate maintaining a low-pressure steam supply while diverting boiler output to critical high-pressure consumers. These are just three examples of the many application possibilities for steam accumulation. The purpose of a steam accumulator is to provide the means to convert an irregular process steam demand into a steady load. The potential benefits are numerous, the primary one being significantly lower energy costs through increased operating efficiency. Additionally, it can provide immediate response to the steam demand, a secure steam supply at constant pressure, temperature and dryness, and will eliminate boiler priming, and high and low water lock-outs due to wide load swings. It can also assure product quality and – where new steam or power plant is required – result in lower capital costs. Crucially, it can achieve all this while reducing environmental pollution.
So what exactly is steam accumulation? In short, it is the storage (in a pressure vessel) of surplus steam produced at
times of low demand for subsequent release to supplement the output of the boiler at times of high demand. Any industrial manufacturing process having a variable demand for steam and where an effective differential exists between boiler and process pressures can benefit from this energy-efficient technology.
How do accumulators work? Water is used as the heat storage medium. The reason becomes evident when the greater heat storage capacity of water is compared with that of the same volume of steam vapour at any given state of temperature and pressure. Most accumulators work on the ‘pressure-drop’ principle, whereby steam from the boiler or waste heat steam generator is charged at high pressure into the water causing a rise in temperature (and pressure) and steam for process is discharged from the water (as ‘flash’) at low pressure to meet the demand.
The size of the storage vessel depends on the difference in pressure raised in the boiler and that of the pressure required by the process, and the amount of storage required. Storage vessels can range in size from 1m3
to 150m3 in volume (and
more), or be a multiple of vessels to achieve the required storage volume.
Steam is an essential commodity for many industrial processes. The technology can be successfully applied to any manufacturing process where steam is used for batch processing or at highly fluctuating rates. These conditions can be found in food production, canning, distilling and brewing, chemical manufacture, textiles, rubber, paper and board, plastics, pharmaceuticals, steel making, laundries, ammunitions, brick and concrete curing, turbine testing, tyre manufacture, combined heat and power. The list is endless! When it comes to the energy saving economics, the most important energy cost savings to be gained from steam accumulation derive from a reduction
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