3.11.3.5 Heat recovery in drying processes
Drying is often a high temperature process and waste heat may be recovered:
●either directly, when the drying process is a direct one using hot air as the heating fluid:
○ mix the exhaust air with fresh air directly before the burner
○ if the exhaust air is contaminated too much (dust, moisture, etc.), recycle heat from exhaust air via an heat exchanger (see Section 3.3.1.) to preheat the product to be dried or the drying air
●or indirectly, using mechanical vapour recompression ( MVR) to compress the exhaust vapour ( see Section 3.3.2), especially when the heating fluid is superheated s team ( see Section 3.11.3.4).
Only 'direct' recycling is considered here.
3.11.3.6 Mechanical vapour recompression or heat pumps with evaporation
Concentration by evaporation coupled with MVR (mechanical vapour recompression) or a heat pump, is a highly efficient technique f or waste water treatment. I n particular, this technique makes it possible to significantly reduce waste water volumes sent to treatment at a low cost, as well as allowing water recycling.
To evaporate one tonne of water, 700 to 800 kWh/t energy power is required. It is possible to reduce the energy needs by using heat recovery solutions, such as heat pumps, including mechanical vapour recompression ( MVR) ( see Section 3.3.2), or multiple effect evaporators with thermo-compression.
3.11.3.5 烘乾過程的熱能回收
烘乾過程往往是一高溫製程，廢熱應可回收。
●直接方式：
○ 直接使用熱空氣當作加熱流體時，把排氣與新鮮空氣混合，當作燃燒進氣。
○ 如果排氣汙染太嚴重(灰塵、水氣)，則利用熱交換器回收熱能，以預熱要烘乾的產品或烘乾用空氣。
●間接方式：使用機械蒸氣再壓縮系統(MVR)壓縮排出蒸氣，特別是加熱流體是過熱蒸汽時。
此處僅關注直接回收。
3.11.3.6 帶有蒸發功能的機械蒸氣再壓縮系統或熱泵
經由MVR或熱泵的蒸發濃縮方法是很高效率的廢水處理技術。可貴之處在於此技術可顯著地減少送到廢水處理廠的廢水量，而且成本低，水可以回收再利用。
蒸發一噸的水需要700~800度的能源(電力)，如使用熱回收方法可節省能源。這些方法包括熱泵、MVR或多效式熱能-壓縮系統。
3.11.3.5 Heat recovery in drying processes
Preheating the air before the burner via heat recovery may disturb the drying process by influencing the temperature-moisture content. Possible contaminants may appear when there is no heat exchanger. Regulation may be needed to correctly control the drying temperature.
3.11.3.6 Mechanical vapour recompression or heat pumps with evaporation
The concentration of waste water streams may require different management and treatment techniques (i.e. may no longer be suitable for waste water discharge).
3.11.3.5 烘乾過程的熱能回收
熱回收尾氣用來預熱燃燒器的進氣空氣，可能會因為溫度與濕度影響而干擾烘乾製程。在沒有熱交換器情況下，可能會出現汙染情況，所以需要正確調整烘乾溫度。
3.11.3.6 帶有蒸發功能的機械蒸氣再壓縮系統或熱泵
不同廢水的濃度需要不同的管理與處理技術，不適合流入一般廢水排放水中。
3.11.3.5 Heat recovery in drying processes
This technique can be used for almost any continuous hot air convective dryers ( tunnel, oven, drum, etc.). Attention is to be paid to burner adjustment and sizing of the different items: fan, pipe diameter, regulation valve and heat exchanger if applicable. Stainless steel is required for the heat exchanger. When the dryer burner works with fuel, exhaust air contains sulphur and SO2 and may damage the heat exchanger if condensation occurs.
3.11.3.6 Mechanical vapour recompression or heat pumps with evaporation
The choice of technology depends on the nature of the product and the concentrate. Feasibility tests can be necessary.
3.11.3.5 烘乾過程的熱能回收
這項技術幾乎可用在連續熱風對流烘乾機中(如隧道式、爐式、滾筒式等)。要注意燃燒器的調整和各項組件(風扇、管徑、調節閥門、熱交換器等)的大小規格要正確。熱交換器必須用不銹鋼製作，如果烘乾機燃燒器使用燃料，送出空氣若含有硫元素或SO2且有凝結現象發生時，可能會損壞熱交換器。
3.11.3.6 帶有蒸發功能的機械蒸氣再壓縮系統或熱泵
依照產品與濃縮物的特性選用適用技術，並且要先做可行性研究。
3.11.3.5 Heat recovery in drying processes
Payback time may be very variable, depending on the energy cost, the evaporating capacity of the dryer and the number of running hours. Never forget to make a simulation with hypotheses on the rise of energy prices.
3.11.3.6 Mechanical vapour recompression or heat pumps with evaporation
Determined on a case by case basis.
3.11.3.5 烘乾過程的熱能回收
投資回收期可能變化較大，端視能源成本、烘乾機蒸發能力以及其運轉時間長短而定。應針對能源價格上漲作模擬分析。
3.11.3.6 帶有蒸發功能的機械蒸氣再壓縮系統或熱泵
依個案決定。
Energy Efficiency (2009) 3.11.3.5、3.11.3.6
