When a UK-based textiles manufacturing plant were looking to increase the energy efficiency of its twin yarn drying process lines ThermTech designed, manufactured and installed a waste heat recovery system which met their needs.
The two dryers originally exhausted both hot and humid air to atmosphere at around 140°C.
A simple, self-controlling and cost effective heat recovery system was required in order to satisfy the following conditions required by the plant:
- Harness the maximum amount of waste heat from the drying process based on varying waste heat source and heat demand
- The dryer gas pressure balance must be maintained under all conditions
- The wash liqueur process streams must not overheat and each stream has its own upper temperature limit
- Each wash liqueur process stream has the potential to suddenly stop and start, while the dryers are running
During an on-site survey, ThermTech engineers initially measured the dryer exhaust gas temperature, humidity and static pressure from the exhaust stack as well as the physical space available on the process building roof before designing a bespoke heat recovery system to suit the above requirements.
ThermTech have successfully harnessed both sensible and latent waste heat from this process in order to provide approx. 2MW worth of wash liquor process heating, resulting in a saving of approximately 3,600 kg per hour of 10 bar process steam, saving natural gas valued at £450,000 per year and 4,500 tonnes of CO2 emissions per year.
Gas Diversion Damper System
ThermTech designed and manufactured a gas diversion damper unit, installed in place of the original dryer exhaust stack in order to send dryer exhaust gases either directly to atmosphere or through the heat recovery unit (HRU).
The dampers allow the amount of waste heat recovered to be automatically controlled to suit the the process condition requirements of the plant. If either of the process wash streams begin to reach a set temperature or stop flowing, the dampers send the hot exhaust gases directly to atmosphere.
Heat Recovery Unit (HRU)
The HRU utilises highly durable extended surface finned tubes to facilitate good gas to liquid heat transfer with a low gas side pressure drop. As the hot gases pass over the finned tubes, condensate forms and flows down the tube bank to the lower transitional section of the unit where it is continuously drained. The effect of condensate raining down over the finned tubes can be observed through the sight port located on the lower transition. The HRU is constructed entirely from stainless steel in order to withstand this condensation effect.
The HRU is split into two separate compartments in order to preheat the two individual process wash liquor streams up to temperature independently of each other.
Both sensible and latent waste heat in the dryer exhaust gases are recovered in the HRU, resulting in a substantial amount of energy savings within a simple and relatively compact design.
The HRU has no moving parts and is self-cleaning due to the continuous condensate flow over the finned tubes. Hence little maintenance / on-line intervention is required.