The most common application for a CHX™ condensing heat exchangers is the recovery of waste heat to preheat boiler make-up water. Preheating make-up water can increase boiler efficiency 3-5% or more. 'l'he heat recovered by a CHX™ condensing heat exchanger can offset much of the extraction steam required by a low pressure feedwater heater or deaerator. This offset will reduce fuel consumption while maintaining a fixed net steam output, or when required. it can increase the net steam output by maintaining the same fixed fuel consumption.
Heating make-up water is not the only heat recovery application for a CHX™ condensing heat exchanger. CHX™ units can have a number of other uses in the plant environment. Applications range from building heat to heating process streams in food processing chemical plants, and various pulp and paper applications.
In one actual installation, a midsized industrial plant has been saving an average of $1,000 per day for the past 10 years in energy costs by heating process water with boiler flue gas. The passively installed system utilizes 160,000 pph of 333° F glue gas to heat 550 8pm of process water from 90° 1: to 136 ° F. The flue gas is cooled to 125 °F. The additional heat recovery has in effect increased the capacity of the plant without requiring the purchase of another boiler. This CHX™ heat recovery system paid for itself in less than 25 months.
CHX™ units can also heat water or process streams indirectly. When a process steam is incompatible with the CHX™ unit design, water or other liquid heat sinks can be circulated in a closed loop through a CHX™ condensing heat exchanger. A closed loop system can be used to heat process streams that are abrasive, corrosive or have a pressure higher than the CHX™ unit design pressure. A closed loop system can also be used for flue gas reheat or in some cases to cool flue gas to a lower temperature where required.
For the past 16 years CHX™ condensing heat exchangers have successfully demonstrated their ability to operate below the acid and water vapor dewpoint to recover low level heat from fossil fueled boilers, HRSG'S and process dryers. While a majority of CHX™ heat exchanger installations have been retrofit applications, there have been several cases where they were included in the heat balance design for new construction or plant expansion.
Based on our experience, the most efficient use for CHX™ condensing exchangers in the future will be for new construction or plant expansion when the customer and their A&E company engineers recognize in the design phase that there will be a continuous requirement to heat a large volume of cold water for a specific use. When the condensing heat exchanger is an integral part of the total project heat balance design it provides the opportunity to maximize the use of the heat recovered to the benefit of the total system heat balance. Another advantage is that the installation cost is typically lower than the cost to interface with existing equipment in a retrofit application.
Cogeneration operators sometimes sell steam or use steam for district heating when it is not possible or not practical to return the condensate back to the Co-Gen plant. These are ideal applications for CHX™ condensing heat exchangers however, they must be included in the original plant design so that the heat balance of the HRSG can be designed to obtain the maximum efficiency for the system when the condensing heat exchanger is included.
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