Textile Manufacturers See Multiple Benefits with Engineering Solutions from Operational Group

Textile manufacturers can boost efficiencies, and reduce their costs and environmental impact, by recycling waste energy and optimising processes with engineered solutions from Operational Group.

We understand the challenges textile manufacturers face and have helped many to optimise their equipment and systems, leading to significant benefits and returns on investment.

One example is Holmfirth Dyers in Huddersfield, West Yorkshire. It operates two stenter ovens to dry and heat-set fabrics after a variety of treatments, such as dying or application of fire retardants.

However, its previous abatement system was not adequately removing knitting oils and a visible plume was seen rising from a chimney stack. Furthermore, the heat recovery process was inefficient, which led to higher steam boiler running costs.

After surveying equipment and processes, Operational recommended the latest generation of electro static precipitator (ESP) abatement systems which offer increased energy recovery.

Procedures include condensing and removing knitting oils from exhaust air, filtering out other contaminants such as textile fibres and recycling heat back into the dyeing processes in the form of hot water. Fan noise was also cut, benefitting residents living nearby.

Neil Shand, an Operational UK senior process engineer, said: “Holmfirth Dyers were keen to follow our recommendations and contracted us to install a complete system and remove the old system. The new equipment included modular heat exchangers to recover up to 837 kW through hot water; a hot water flow control to maintain optimal temperature for the abatement system, giving a finely-controlled water outlet temperature of 70oC for other processes; and optimisation of the exhaust air extraction system.

“We also installed a wash cleaning system to extend the intervals between deep-clean maintenance, a steam fire extinguishing system to enhance safety, and an oil-water separator to initially separate the waste streams to minimise further treatment.”

The calculated return on investment for Holmfirth Dyers is just under three years.

Explaining the details, Neil said: “The stenter exhaust temperature varied between 120 oC when drying and 160 oC when heat-setting. This offered significant scope for heat recovery, especially because large volumes of hot water are used in the dying process.

“The exhaust air flow from each stenter varied between 7,500Nm3/h and 15,000Nm3/h. So the extraction system needed to be variable to compensate for the changing inlet conditions.

“As part of the emission abatement scheme, exhaust gasses are cooled to initiate condensation of knitting oils. We designed heat exchangers to maximise recovered heat while still achieving the required condensation efficiency and maximising the hot water temperature to give the best heat density.

“In addition to oils, stenter exhaust air contains other contaminants such as fibres and significant water vapour. So the selection of heat exchangers is critical. We installed a two-stage filter mesh to reduce fouling. The fin pitch of each of the three banks of heat exchangers also had to be considered for fouling, so we designed a wider pitch at the start to reduce the likelihood of blinding due to fouling on the air side from fibres and condensate.

“The heat exchangers were also designed as a cartridge insertion-type for improved maintenance. The air is cooled to condense the contaminants into a very fine droplets fume. Again to avoid fouling and reduce maintenance, the system was installed with fixed cleaning nozzles to allow a wash-down cycle.

“The next step passes the fume through a Euroklean filter element to create coarser droplets. The air then passes through the tubular ESP section where a very high voltage of 15,000 V is applied, although only a small current of up to 40mA per pass is drawn. This charges the droplets and makes them drift to the earthed tube walls for draining.

“The ESPs have an electronic control circuit to monitor current and voltage. This reduces the risk of arcing, maximises efficiency and gives detailed fault analysis. Five passes of ESP are installed to maximise the accumulative efficiency.

“An automated wash system was also put into the first two passes of the electro static precipitator (ESP) system. The water could be pre-heated using a steam to water plate heat exchanger, the pre-heat could be carried out offline.

“Before passing through a pressure-controlled exhaust fan, the exhaust air goes through a mist eliminator pad to capture any re-entrained liquid. The fan outlet was then treated with a silencer to reduce noise.”

In summary, Neil added:“ Holmfirth Dyers is very happy. It now has a discharge from the stack with no visible emissions, lots of recovered heat and enough hot water for their dye-house and other requirements.

“They have also used Operational for a full maintenance service package. Our previous service included intensive cleaning and ESP maintenance, to avoid a build-up of oil which can cause short-circuiting. Now we ensure general cleanliness for operation with quarterly intensive cleans.”