POLLUTION PREVENTION ASSESSMENT FOR A TEXTILE DYEING FACILITY SERVING FABRIC MANUFACTURES --------------------------------------------------------------- CASE STUDY I Summary --------- This assessment evaluated a dye house serving a variety of fabric manufacturers. The objective of the assessment was to identify actions that would : (1) reduce the quantity of toxics, raw materials, and energy used in the dying process, thereby reducing pollution and worker exposure, (2) demonstrate the environmental and economic value of pollution prevention methods to the dyeing industry, and (3) improve operating efficiency and product quality. Overall, the assessment identified 37 pollution prevention opportuniies -- classified as first, second, and third priority opportunities -- that could reduce energy use at this facility and avoid the release of over 14 metric tons of air emissions each year, in addition to unquantified reductions in the release of global warning gases and heavy metals. Water use could be reduced by 125,000 cubic meters per year, and chemical releases to surface waters could also be reduced. Finally, it may be possible to avoid the disposal of 330 cubic meters of solid waste per year. Facility Background -------------------- This facility is a dye house serving fabric manufacturers. The facility operates two eight-hour shifts, six days per week, employing seventy shift workers and twenty technical and administrative employees. In 1992, the facility processed 350,000 kg of cotton and 360,000 kg of wool fabric. Manufacturing Process ---------------------- In general, cotton dyeing involves two procedures, desizing and bleaching, and dyeing. Each procedure involves a number of steps that must be carried out in proper sequence and under optimal conditions. For detailed depictions of these processes, see Flgure 1. Wool dyeing also involves several procedures: (1) washing, (2) podding (heating thin wool fabrics in lint washed off fabric, (4) leakage of detergent-laden water from the wool washing machines, (5) excessive pH of effluent from the decarbonizing acid bath, (6) excessively hot effluent, (7) excessive oil and grease and sulfate concentrations in effluent, (8) leakage from steam coils, (9) hydrogen sulfide generation at the wool laundry sump, (10) disposal of dry wool, cotton combings and shavings, and sodium sulfate bags (materials that could be recycled), (11) excessive air emissions of particulates, and (12) lint and sulfuric acid mist in the wool laundry room. This facility uses about twice as much water as the average commission batch dyer its size; thus, many of the recommendations focus on reducing water consumption and the energy required to heat it for various dyeing processes. Pollution Prevention Opportunities ----------------------------------- The assessment identified almost 40 pollution prevention opportunities that could address the problems identified. With significant environmental and economic benefits to the facility. The assessment team prioritized these opportunities based on pollution prevented and implementation cost. Table 1 lists the high priority opportunities recommended for the facility and presents the environmental benefits, savings and implementation costs, and estimated pay back period for each. Many of the recommendations can be implemented with no capital investment. Further, many can be implemented almost immediately, and most are not dependent upon other projects for their initiation. Of the 19 high priority opportunities recommended, the savings possible from implementing six have been quantified. These six recommendations will reduce operating costs by almost $106,000 per year for an initial investment of $1,900. The simple payback period for these changes is one week. Another $2,600 in investments is required to implement other changes whose savings potential cannot be quantified without further research. Implementation of the recommended actions will produce positive environmental impacts in three areas; reduced air emissions, lower water and chemical use, and reduced generation of solid waste. Air Emissions. Many of the proposed changes will reduce steam consumption and lower fuel use, thereby reducing air emissions. Repairing all traps should reduce fuel consumption by 36 percent, or 454 metric tons of number 6 residual oil per year. The expected reductions in air emissions from this change total over 14 metric tons per year. In addition, this change will result in reduced carbon dioxide and heavy metal emissions. Water and Chemical Use. When all rinsing changes have been imple- mented, the facility should consume half the water it currently does. The yearly reduction in water use will about 125,000 cubic meters. Chemical use will decline due to a number of changes. Sulfate in the effluent will be reduce by more than 70,000 kg/year by changing to sodium chloride and filtering the decarbonizing acid bath. Releases to the sewer of other chemicals such as dey, dye stabilizers, de-foamers, detergents, sodium hydrosulfite, bleach, optical brighteners, acetic acid, equalizers, and boiler treatment chemicals will be reduced as a result of the recommended changes. Among the changes that will affect chemical releases are : (1) better process controls, (2) screening drains and cleaning sumps regularly to prevent sulfide generation, (3) preventing beck boil-over, (4) repairing coil steam leaks that contaminate boiler feed water and process baths, (5) using a lower-foaming jet-dye detergent, (6) calibrating and shimming becks, (7) repairing and modifying becks and wool laundries, and (8) determining sizing formulae. Unitl these changes are made, it is not possible to calculate the degree to which releases will be reduced. Solid Waste: Solid waste discarded by the facility consists mainly of sulfate chemical bags and shavings and combings from fabric finishing. Assuming that the eight sulfate bags generated per day fill one large (0.1 cubic meter) garbage bag and that the combings fill ten bags per day, the yearly un-compressed volume of these solid wastes is 330 cubic meters. If both wastes are recycled, this volume of waste can be reused at least once before being discarded. CASE STUDY -II --------------- Summary --------- This assessment evaluated a dye house serving a variety of fabric manufacturers. The objective of the assesment was to identify actions that would: (1) recuce the quantity of toxics, water, and energy used in the dyeing process, thereby reducing pollution and worker exposure, (2) demonstrate the environmental and economic value of pollution prevention methods to the dyeing industry, and (3) improve operating efficiency and product quality. Overall, the assessment identified eleven pollution prevention opportunities that could reduce energy use at this facility and avoid the release of 0.5 metric tons of air emissions each year. Water use could be reduced by nearly 70,000 cubic meters per year, and chemical releases to surface waters could also be reduced. Two of the opportunities - recycling bleach rinse water and capturing the heat in boiler blowdown water - reduced annual operating costs by about $9,000 for an initial investment of $1,700. Facility Background -------------------- This facility is a dye house serving fabric manufacturers. The facility operates two twelve - hour shifts, six days per week. In 1992, the facility wet-processed about 960,000 kg of fabric, consisting primarily of cotton-synthetic blends. Manufacturing Process ---------------------- Fabric dyeing at this facility involves a number of steps that must be carried out in proper sequence and under optimal conditions. The process consists of filling tanks containing fabrics with water, and sequentially (1) heating, (2) rinsing, (3)adding dyes, bleaches, and other chemicals, (4) colling, and (5) combing or ironing the fabric. This process involves at least eight complete changes of water, and at least six additions of dyes, bleaches, and other chemicals. Existing Pollution Problems ---------------------------- At the time of the assessment, there were a number of pollution problems at the facility, including (1) excessive water use in the rinsing, dyeing, and bleaching processes, (2) excessively hot effluent, (3) unnecessary energy use due to ineffective heat recovery, (4) excessive BOD of effluent, and (5) overuse of dyes and other chemicals. Pollution Prevention Opportunities ------------------------------------ The assessment identified eleven pollution prevention opportunities that could address the problems identified, with significant environmental and economic benefits to the facility. Table 1 lists the opportunities recommended for the facility, and presents the environmental benefits, savings and implementation costs for each. Many of the recommendations can be implemented with no capital investment. Further, many can be implemented immediately, and most are not dependent upon other projects for their initiation. The recommendations can be grouped into four general categories: (1) reductions in water use, (2) modifications to recover waste heat, (3) proces control modifications, and (4) reduction in effluent contaminant concentrations. Table 1 : Summary of Recommended Pollution Prevention Opportunities ---------------------------------------------------------------------- Unit Pollution Prevention Environmental Benefit Capital Cost Operation Opportunity and Cost Savings to Implement ---------------------------------------------------------------------- Bleach Reduce water use, Reduce water use by $1,200 to Rinsing recover process 23,000 cubic meters replumb tanks chemicals and heat per year. Reduce water by recycling bleach costs by $6,300 per rinse water. year. Dye Reduce water use by Reduce water use by $2,400 for Rinsing recycling second dye 43,000 cubic meters two tanks rinse. per year. Reduce water and Plumb- costs by $12,800 per ing. year. Boiler Recover heat from Reduce fuel used by 500 boiler blowdown. 2,700 per year, reduce temperature of effluent. Dye Reduce liquor ratio Reduce water use by up None Process in jet dyeing to 4,800 cubic meters per year. Reduce water costs by $1,300 per year. Chinese Control dye process Reduce redye and chemical None Reactive using Fong equipment costs (unquantified). Dyes Dey Use Fong equipment Reduce use of chemicals, None Process to determine acetic reduce BOD 5 of effluent and formic acid (unquantified). concentrations for specific dyes. Reactive Determine actual Reduce dye use, decrease None Dyes price break point cost of dyeing (inquan- for one and two-step tified). dyeing. Dispersed Change dyes to imp- Reduce dye in effluent None Red 60 rove heat fastness. reduce dye cost Dye (unquantified). Effluent Reduce suspended Keep effluent in 120 solids in effluent compliance . by installing screens Reduce sulfide in Reduce sulfide in eff- 120 effluent by aeration luent, prevent sewer and exposure to deterioration. light. Determine effluent Keep effluent in com- $600 for concentrations for pliance, identify testing controlled para- priority pollutants meters, determine for reduction. reduction priorities. TOTALS $9,000 to $23,000 $2,500 to annually, plus unq- $5,000 uantified opportunities. ---------------------------------------------------------------------- Reductions in Water Use. Water use at the facility is now near the limits of system capacity. The resulting low water pressure increases the cycle time for fabric processing by extending the time needed to fill jets with water. Any reduction in water use would therefore increase productivity as well as reduce water purchase costs. If large quantities of the same colored fabric dyed in succession, countercurrent rinsing can be built into the structure of jet dyeing equipment. This would reduce water use, while maintaining the same quality of final product. Bleach rinsing involves two successive overflowing rinses. Recycling the second bleach rinse back into the process for use in the first rinse could begin immediately to reduce water use; water reuse is standard practice on large through-put machinery. Assuming that half of the 8,200 liters used for the two bleach rinses is reused and that 5,680 loads per year are processed, the quantity of water that could be saved is 23,300 cubic meters per year, saving over $6,400. If rinse processes are modified to use recycled second rinse water, the additional savings would be 43,300 cubic meters per year worth $12,800, for a total savings of nearly 70,000 cubic meters per year worth almost $20,000. If water from both rinses is recycled, total water use could be reduced by about 25 percent. Modifications to Recover Waste Heat. Currently, after polyester dyeing, the solution in the jet is cooled with a heat exchanger from 130 degree C to 80 degree C. By retrofitting the boilers with a continuous blowdown system, and routing the water from that system through the heat exchange coils in the two steel tanks, heat could be recovered into the used jet cooling water. Water for both fabric processing and boiler feed could be drawn from this tank, which would make maximum use of the heat from both jet cooling and boiler blowdown water. The savings would be about $2,700, assuming a 50 percent efficient heat transfer mechanism. Reusing rinse waters and capturing heat from the boiler blowdown also reduces the temperature of effluent. This is significant because effluent has sometimes exceeded 75 degree C, when the standard is 35 degree C. Process Control Modifications. Jet dyeing equipment of the type used at the facility could be run at lower liquor ratios than the current 10:1, perhaps as low as 5:1. Reducing the liquor ratio to 5:1 would save 4,800 cubic meters of water per year, worth over $1,300. Additional unquantified savings might be gained through better dye utilization. In addition, the facility could use a dye process simulator to realize significant savings by individualizing dye process formulae to the facility's unique needs. The facility could also use this equipment to help optimze the use of chemicals such as acetic and formic acids, which are the two largest contributors to biological oxygen demand in the effluent. Use of less expensive Chinese reactive dayes requires a two-step process that consumes more time, water, and energy than the one-step process that can be used with more expensive European dyes. The facility can conduct a detailed study of these two methods, comparing the cost of all inputs, not just the purchase price of the dye to determine which dye type best meets the facility's overall manufacturring goals. Reduction in Effluent Contaminant Concentrations. The facility could install parallel bar screens in the het room where drains meet and at the entrance to the main sewer sump to reduce the amount of toal suspended solids and sedimentable solids from fabric lint in the facility's effluent. More efficient removal of lint would reduce the amount of organic material in the sump, thereby depriving bacteria of food. Sulfide and heat in the effluent also may be reduced by replacing the cover on the sump with a grate that allows light and air to enter. This would promote oxygenation, allow hydrogen sulfide to dissipate, and increase heat exchange, thereby cooling the effluent. SOURCE : CTEM PUBLICATION DATE : 15TH MAY, 1999