Written by Dr. Nagarajan G
Published in Textile Value Chain - Nov 2023
Abstract
Maintaining appropriate relative humidity and temperature inside the department is essential for satisfactory working performance in the textile industries. In addition, comfort of the personnels working inside the department is equally important for enhancing the efficiency. The modern concept in textile industries is the adoption of Air Engineering. Air Engineering not only controls the relative humidity but also assists in removal of waste from the machineries to the Centralised Waste Evacuation System (CWES). This ensures a dust free working atmosphere in the department with acceptable breathable dust. (50µm)
1.0 Introduction
In today’s rapidly growing environment and the stringent requirement required to be maintained in the textile industries, maintaining of proper relative humidity and temperature is of paramount importance. Many suppliers are providing the humidification plants with their improved design concepts in air washers, dampers, filters etc. for better working environment in the textile mills. Essentially textile air engineering fulfils two main objectives. First, it makes an important contribution to increase the productivity and quality in processing natural and synthetic fibres. Second, improving the hygienic working conditions for the personnels working in the textile plant. There are three major areas in the air engineering, namely, air conditioning, pneumatic machinery cleaning as well as filtration and waste removal. Textile air Engineering was specially developed for the industry demand and manifold requirement of the textile industry. Pneumatic machine cleaning consists of appliances, which through aerodynamic effect collect, extract and separate waste, dust, fibres heat, vapour and exhaust gases. These appliances form an integral part in the Air Engineering or can be used as accessories. Filtation and waste removal eliminates the impurities and loose fibres that are released in the production department. Before the development, the wastes are removed manually by hand, however, at present it is fully automated thus satisfying the stringent regulations laid by OSHA standards. The integration of these three fields into a comprehensive system is designted as TAC (Total Air cleaning and Control).
2.0. Air conditioning
The threefold functions of an industrial air conditioning system are:
To provide the required levels of relative humidity (RH) required for optimal working conditions in the department.
To provide a specified dry bulb temperature for the comfort of the personnels inside the department
To circulate enough air by removing the heat load generated inside and infiltration from outside as well.
The required air circulation in CFM cubic foot per minute) is calculated by
CFM = Heat load B.T.U./hour
1.08 x (Inside Dry bulb temp – Outside dry bulb temp) ÷ F
3.0. Importance of Air Conditioning
Humidity
Maintaining proper relative humidity level is essential for smooth operation of the machines and processes. Moisture reduces the formation of static electricity while processing synthetic fibres and blends. However, on the other hand, higher humidity increases the chances of roller lapping and also reduces the degree of opening in disentangling the fibres. Furthermore, the breaking force and elongation are directly influenced by the ambient relative humidity conditions in the department. Optimum values depend upon the type of raw material used for the yarn production. A higher relative humidity will result in a lower room temperature during the evaporative cooling process.
Temperature
In general, temperature fluctuations vary from place to place depending on the geographical location of the textile plant. There are are some processes which are temperature sensitive such as weaving. However, all processes require a constant temperature, as most natural fibres are hydrophilic and hence the moisture absorbing capacity changes with temperature. In addition, reducing count variation in textile mills, control of temperature has a positive effect on fibre fly, fewer electronic components failures, better working environment. In summer and monsoon seasons, daily room temperature fluctuations can be minimized by using refrigerant cooling instead of evaporative cooling method.
Fibre recovery and Handling
Most of the modern textile spinning machines have integrated suction points that can be integrated in to a centalised fibre deposit system. The fibre separation and dust filtration plant must be designed in such a way that it should be capable of handling the required volume and under pressure and also the amount of waste fibre. Based on the raw material used, fibre separators are installed to separate the fibre mixtures.
Modern air engineering plants are integrated with bale press system to collect the waste briquettes which reduces the personnel intervention and increases the efficiency of the bale press.
Clean working atmosphere
In order to control the fibre fly/dust contamination and dust infiltration into the department, the factory is kept at constant overpressure. Based on the potside air contamination, fresh air filters and depending on the process requirements, supply air filters are required. This is very important to maintain Permissible exposure Limits (PEL) to protect the health of the personnels from byssinosis.
4.0. Components of Humidification system
Most of the humidification plants supplied by various manufactures have
Air washers
Spray piping
Water eliminators
Inlet louvers
Rotary air filter
Dampers
Axial flow fans
Automatic control system
Air washer system
Air washer systems are designed considering all the heat load in the department and required RH to be maintained in the department. The supply and return air system is designed based on the heat load in the department. It is designed in such a way that the whole department is maintained at positive pressure for better elimination of fibre fly and dust from the department. Return air supply is designed to with return air grills and slit opening to maintain with specific negative pressure thus necessitates a clean working environment and also the removal of heat from the motors effectively as well. Air washer efficiency should be around 80% for effective working conditions.
Spray piping or Nozzles
The spray piping or nozzles should be corrosion free, leakage free with extra heavy duty PVC piping and non-clog polycarbonate nozzle. Nozzles should give fine hollow spray with wide angle.
Water Eliminator
The eliminators are designed in such a way that it provides fine water droplets inside the department instead of water droplets in the form of rain. This would cause difficulties in working and also damage the machine condition as well. Various range of water eliminators are available with PVC fins which offers less resistance to air flow besides being light and durable. The eliminators should have reduced pressure drop, low maintenance cost, less capital investment with longer working life.
Inlet Louvers
The PVC louvers are PVC hollow “Z” type which sucks the air forms an air current equally all over the width of the air washer and thus helps to achieve more saturation efficiency.
Rotary Air filter
Rotary air filters have rotating drum made of steel grid mesh with suitable mounting frames driven by a separate geared motor suitable to provide large filtration area. The air laden with fibre and dust collected on the drum are arrested on the surface of the filter media covering the rotating drum and it is sucked by suction nozzle arrangement with to & fro motion connected to flexible hose arrangement. This arrangement continuously cleans the fluff & dust collected on the filter media and collected in a separate waste collection bag. Suction fan with collection unit is housed in a separate room next to the filter room.
Low pressure drop is maintained due to high pressure cyclone fan to work effectively not only to remove the fluff collected on the filter surface media and dust get arrested in the filter pores. This provides uniform return air flow at high pressure so as to continuously remove fluff and dust from the department to maintain a clean working atmosphere.
Axial Flow fans
The main component which accounts for more power consumption in an air conditioning system is Axial flow fans. It accounts for about 55% and 75% in spinning and weaving units respectively of the total electrical energy consumed. The latest generation fan blades are made of very light and high strength “Hybrid Long fibre compound” material. These fans have wider operating ranges, improved aerodynamics and efficiency and lower stresses while during continuous operation.
Automatic control system
Automatic control systems ensure proper RH & temperature with extremely sensitive dry bulb and wet bulb temperature sensors. Temperature is controlled by opening and closing of fresh air, return air and exhaust air dampers automatically with the help of actuators. Humidity can be controlled by using bypass dampers. It means that central monitoring system ensures proper control of RH inside the department round the clock with the computer.
5.0. Refrigeration system
In general, during the cold weather periods, there is no problem to provide the conditioned air to the production areas with adequate conditioned air and maintain the temperatures for both men and machines. However, during the peak summer seasons where the outside temperature exceeds those of a dew point temperature which corresponds to the maximum permissible room temperature of 28÷C.
The air conditioning plants therefore has to be supplied with chilled water constantly, which after being heated up, is then returned to the refrigeration plant where it is cooled down by two centrifugal liquid chillers. The heat which is removed from the production areas through the chilled water circuit, is then transferred to the cooling water circuit. The heat removed is then blown away to the atmosphere through cooling towers.
6.0. Conclusion
The effective utilization of men, machines and the raw material depends on many factors like process optimization on machines, speeds etc. Nevertheless, the importance of maintaining proper relative humidity and temperature has also to be considered for achieving maximum efficiency with acceptable output product. For a clean process, air conditioning plant has an advantage over a simple ventilation system like automatic control of RH, automatic removal of waste from the machines and handling those waste materials in centralized waste evacuation plant. However, the installation of chiller plant is quite expensive as humidification plant consumes 15 to 20% of the overall powercost which has to be borne in mind.
References
Jones M.C., Air Conditioning - Journal of Textile institute Proceedings 46:8, P 470 to P 490. 1964.
Luwa Ltd, Zurich, Swizz, Air Conditioning – Asian Textile Journal , May 1993