Cleaner production: an industrial example

Cleaner production: an industrial example*

James W. Clements and James P. Thompsont

Commercial Polymers Pty Ltd, Maidstone Street, Altona, Victoria 3018, Australia

Received 7 September 1992

A polyethylene plant at Altona has made significant progress towards cleaner production over its 30 year life. The original high pressure plant built in 1961 has been modernised, resulting in improved productivity and reliability and consequently in reduced emissions. The UnipolTM low pressure polyethylene process, which has inherently clean environmental performance, was first introduced in 1972. The gradual shift in production capacity to this process has enabled significant waste reduction and improvements in energy use per unit of production. However, the highlight of the move to cleaner production has been the achievement of zero discharge of wastewater offsite. This has been achieved by water conservation combined with a system of wastewater treatment, recycling and land disposal.

Keywords: industrial production; wastewater discharge; water conservation; polyethylene production

Introduction Commercial Polymers Pty Ltd (COMPOL) is a polyethylene producer operating in the Altona Chemical Complex in Victoria, about 15 km west of Melbourne*. The plant has been producing polyethylene since 1961. It is presently managed by Mobil Chemical Company on behalf of its shareholders Mobil Oil Australia Limited and Esso Australia Limited. It is the only Australian plant to produce all three types of polyethylene: low density polyethylene (LDPE), high density polyethylene (HDPE) and linear low density polyethylene (LLDPE).

Two very different processes are used to make these polyethylene types. The LDPE is produced by the conventional high pressure polyethylene process. This was the original polyethylene process which was commercialised in the late 1930s. The high pressure plant was designed in the late 1950s and came onstream in October 1961 using a Union Carbide Corporation tubular reactor design. The process uses extremely high pressure, often more than 2400 times atmospheric pressure.

By contrast the more modern types of polyethylene, HDPE and LLDPE, are made by COMPOL using the Unipol gas phase technology. This process uses low pressure of about 20 atm which is around 1% of those used in the high pressure process. The COMPOL low pressure plant came onstream in 1972 and was one of the first such plants built outside the United States. Today there are more than 60 Unipol PE reactors operating in 19 countries.

* Paper presented at the Asia Pacific Cleaner Production Conference t Correspondence to Dr J.P. Thompson $ Commercial Polymers Pty Ltd operations merged into Kemcor Australia Pty Ltd, a Mobil Exxon joint venture, from 1 December 1992.

0969-6526/93/01/0015-05 0 1993 Butterworth-Heinemann Ltd ’

The environmental performance of the Unipol process is well documented’. The process has a number of inherent environmental advantages including the use of gas phase instead of liquid and its low operating pressures.

At the Altona site there has been a transition from a single reactor high pressure plant to a plant where the majority of polyethylene production is derived from the low pressure unit. In addition significant productivity gains have been made in both units. The net effect of these changes has been a steady improvement in the environmental performance.

This paper compares the current environmental performance of the two processes operating at the site and some of the environmental trends in waste generation over recent years will be examined. The paper will then focus on cleaner production achieved by the management of water and wastewater at the plant. This program has seen the water usage decrease significantly and the site achieve a zero discharge of treated wastewater offsite.

Waste generation Solid and liquid wastes

Wastes are generated by most chemical processes but judicious application of waste minimization at the design stage and in the operation of the plant does lead to cleaner production.

The inherently cleaner nature of the Unipol low pressure process can be seen from an analysis of the Environment Protection Authority of Victoria EPAV Prescribed Wastes* generated during 1991. This shows that the low pressure process produced only one quarter of the waste that was produced by the older high pressure process (see Table I).

Certainly, more recently constructed high pressure

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Cleaner production: an industrial example: J. W. Clements and J.P. Thompson

Table 1 Breakdown of 1991 prescribed wastes by per cent

Low High pressure pressure process process Totals

Contaminated resin Catalyst manufacture waste Gas purification catalyst waste Reaction by-products Waste oil Miscellaneous others General plant wastes

Total waste 32 68 100 Total waste (kg/tonne product) 2.0 8.6 4.2

12 8 8

- -

1 3

19 31 - 8 - 8 20 20 2.5 25

1 2 3 6

units using more up-to-date technology would generate lower waste quantities. As an example, 25% of this plant’s waste stream results from oil generated by the high pressure pumping system. Modern designs utilize hyper-compressors which do not generate this type of waste.

However, cleaner production can still be achieved using old processes. Modernizations incorporating new technologies and a better awareness of waste minimization have meant significant reductions in the generation of waste. The waste oil generation from the high pressure plant has been reduced significantly over the past ten years as demonstrated by Figure 1. The marked reduction in 1987/1988 was achieved by rationalizing the equipment used for high pressure pumping.

Hydrocarbon emissions

Waste minimization techniques have also been applied to the emissions of hydrocarbon to the atmosphere. Emission reductions have been driven not only by tighter licensing requirements but also by the major economic benefits to be gained from reducing the amount of expensive materials lost in the production process. Ethylene efficiency measures the overall conversion of ethylene to polyethylene and therefore the related levels of ethylene losses and atmospheric hydrocarbon emissions. The significant improvement

300 , I

250

“0 200 3

5 150

2 100 0

50

0 I979 1981 1983 1985 1987 1989 1991

1980 1982 1984 1986 1988 1990

Year

75 ” “‘I ” ” ” ” ” “1’ ” ” ““‘I 1961 1965 1969 1973 1977 1981 1985 1989

1963 1967 197’ ‘975 I979 1983 ‘987

Year

Figure 1 Hydraulic oil usage, 1979-91 Figure 2 COMPOL plant ethylene efficiency

in Figure 2 indicates the reduction in atmospheric hydrocarbon emissions over the life of the polyethylene processes. The introduction of the low pressure process in 1972 and the shifting of capacity away from the high pressure unit has contributed to this increased ethylene efficiency.

The major source of emissions from the two polyethylene processes is fugitive leaks for valves, PSVs pumps and compressor. An active leak detection and repair programme began in 1990, covering over 1000 valves and 40 pumps and compressors. Leaks have been reduced significantly. In the past two years the number of leaking valves alone has fallen nearly 40% as a result of the programme.

Total atmospheric hydrocarbon emissions from the high pressure process have been estimated to be around 5.2 kg tonne-l of product and for the low pressure process around 1.2 kg tonne-’ of product in 1991. The difference in these emissions can again be attributed to the process differences. Residual ethylene monomer is present in the resin produced by both processes, however due to the technically more advanced resin purging and recovery systems in the low pressure process, the evolution of residual levels of monomer in resin produced this way are far lower. This results in lower hydrocarbon emissions from the low pressure plant resin storage bins.

Atmospheric hydrocarbon emissions from the low pressure plant are also minimized by the utilization of a flare system. The flare system captures safety valve discharges and process ventings, again reflecting the improved technology available when the low pressure plant was designed and which was not a part of the design philosophy for the older high pressure plant. In the high pressure process, substantial reductions in atmospheric emissions have been achieved by developing more reliable reactor operations with fewer upsets that can cause atmospheric venting.

Energy utilization

Any consideration of cleaner production must include the important parameter of energy consumption. Significant savings can be made and, at the same time, carbon dioxide emissions from power generation can be reduced. Figure 3 demonstrates the reduced electrical energy consumption over the past 30 years.

The initial reductions in energy consumption were

J

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Cleaner production: an industrial example: J. W. Clemenrs and J. P. Thompson

B,.,I I I I I I I I 1960 1965 1970 1975 1980 1985 I990 1995

Year Figure 3 COMPOL electrical energy consumption

achieved in the high pressure plant, which was the only unit operating until 1972, by improvements in catalysts used together with advances in high pressure reactor technology. After 1972 the reduction resulted from progressive increases in the proportion of low pressure production which uses much less energy, coupled with very significant improvements in low pressure reactor productivity (see Table 2).

Wastewater management By far the most significant contribution to cleaner production at this plant has been its innovative wastewater management programme. The programme has four key elements which have made this achievement possible - water conservation, wastewater treatment, recycling of treated wastewater and land disposal of any surplus treated wastewater. The site produces about 600 ki per day of wastewater which is treated and then recycled or used on site. No connection exists to the municipal sewer and the site has, since March 1984, achieved zero discharge of process wastewater offsite.

Water usage

Water conservation has been critical to the site’s water management programme. There are over 20 water meters, read on a daily basis, that monitor water used throughout the plant. Analysis of these results allowed high consumption areas to be targeted and water intake minimization strategies to be adopted. Figure 4 depicts water usage over the past 10 years. In the early 1980s water usage was reduced by about 30% from 800 m3 per day to a minimum of just over 500 m3 a day in 1985. Less attention to water usage in recent years has seen the figure creep back to 600 m3 a day in 1990 and 1991. However, action taken in late 1991

Table 2 Electrical energy consumption

High Low pressure pressure plant plant

Total electricity utilization (kWh kg’) 1.8 0.7 Total carbon dioxide generated due to electricity generation (tonne/tonne product) 2.3 0.9

b& ’ ’ ’ ’ ’ ’ ’ ’ I ’ G II d 1980 1983 1984 1985 1986 1987 1988 1989 1981 1982 1990 I991

Year Figure 4 Historical potable water consumption, 1980-91

means water usage is expected to return around 500 m3 per day.

The technological differences between the high and low pressure processes is again evident in their relative waste consumption. The low pressure plant consumes 0.26 kl tonneel product, 10% of the 2.87 kl tonne-’ consumed by the high pressure process. This is mainly because the older process relies on a water slurry system to convey polyethylene granules, whilst pneumatic conveying is used in the low pressure system.

Wastewater tieatment plant

Treatment of process wastewater and septic waste from COMPOL’s manufacturing facilities occurs in the wastewater plant depicted in Figure 5. This is an elaborate activated sludge unit operating in the extended aeration mode. The plant was installed in 1974. Plant effluent, after removal of oil and polyethylene resin, is pumped to a retention tank with a volume equivalent to one day’s process flow. This serves to average out hydraulic and organic loadings on the treatment plant.

From the retention tank, effluent flows to the oxidation channels where it undergoes biological oxidation. Treated sewage from the septic tank system is also added to these channels. Water and sludge then pass to an upflow clarifier where sludge is separated for recycling to the oxidation channels. Chlorine is added to disinfect the water prior to recycling or land disposal.

Wastewater quality

The treated effluent is licensed by the EPAV, Table 3 details some of the key water quality parameters averaged over 1991. As can be seen the water quality is excellent for reuse and land disposal with levels well within EPAV licence limits. (For further details of wastewater quality, see McKie3).

septic waste

Chbrm Treated waste water

+z!x

API pit Influent RetmhM Oxldatlon separators P’t tank channels

Figure 5 Wastewater purification plant

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I



Table 3 Quality of COMPOL treated wastewater 1991

Parameter Treated wastewater

EPAV median licence limit

Suspended solids (g mm3) 5.5 30 E. Coli (orgs/KKl ml) 25 1000 BODS (g m-‘) 4 20

Cooling towers (71.1%) Flood irrigation (6.7%)

Garden irrigation (3.4%)

Spray irrigation (I 6.1%)

Figure 6 Treated effluent distribution, 1991. Based on average WWPP throughput of 459.7 kl per day

Recycling of treated wastewater

Since the drought of 1972173, wastewater has been recycled to the cooling towers. Over 70% of the treated wastewater was recycled in 1991 and the balance was flood and spray irrigated on 37 hectares of company land at the rear of the manufacturing site or used on the company gardens (see Figure 6). The schematic flowsheet of water use at the manufacturing site is shown in Figure 7.

The installation of sand filters in 1987 and the use of a flocculant in 1990 have dramatically reduced the suspended solids in the treated wastewater from around 15 mg 1-l in 1986 to less than 5 mg 1-l in 1991. This has reduced the amount of underdeposit corrosion and fouling experienced in the plant’s cooling water system.

Poto ble 1 water t Evaporation

I Side stream filter

Process waste water

Waste water treatment

plant T Cooling water - make up filter

II

Excess effluent to 7 land disposal

Figure 7 Schematic Rowsheet of water use at COMPOL Figure 8 COMPOL irrigation layout

Land disposal

When the Altona Chemical Complex commenced operation in the 1960s all the companies discharged their effluent via a common pipeline to Kororoit Creek, some 2 km east of the Complex. As a result of increasingly stringent discharge requirements fore- shadowed by the EPAV in the late 1970s and early 198Os, the seven Complex companies examined alternatives for future wastewater disposal.

COMPOL decided on a land disposal scheme because of the high quality of treated wastewater, the low volume of residual effluent after recycling, the large area of flat land and suitable climate. Five of the other complex companies decided to discharge to sewer while the remaining company Dow Chemical Australia Limited opted for a land disposal system by drip irrigating a specially established tree plantation on its land. The site has 37 hectares of vacant land and seven hectares of this is used for spray irrigation. The irrigation system consists of over 100 sprinklers, each with a capacity of 1 1 s-l. Figure 8 is a schematic of the site. This also shows the flood irrigation area which acts as a safeguard against a breakdown of the spray system.

The EPAV land discharge licence was issued in December 1983 and the system commenced operation in January 1984. Since March 1984 no treated wastewater has been discharged to Kororoit Creek. An urban forest was planted in 1984 with over 1000 native trees. Today many of the trees are more than 5 m tall and another 2000 additional trees have been added to the original plantation. The forest has been successful in stopping spray from the sprinklers drifting off site. The holding dam was built in 1985. This serves as winter storage for surplus water. The water can be returned to the wastewater plant for recycling or for spray irrigation in summer. The dam also catches any run off from the spray irrigation plot to its immediate north.

The dam has a maximum capacity of 50 megalitres and covers 5 hectares. In 1987 the dam was stocked with silver perch fingerlings about 3 cm in length. By 1990 they had grown to over 30 cm in length and weighed over 500 g. Two of the fish were analysed for the presence of the heavy metals: zinc, chromium,

Fire training ground

Monufocturing site

18 J. Cleaner Prod. 1993 Volume 7 Number 1


Table 4 Guahty of Silver perch (concentration in mg kg-’ net weight)

Metal COMPOL Perch

NHMRC standard Lake Colac Redfin

Zinc 6.3 150 %7 Chromium ~0.1 No standard 0.3-0.8 Lead co.1 1.5 0.6-0.9 Cadmium co.02 0.2 0.01-0.02 Mercury 0.33 0.5 0.05-0.19 Copper 0.94 10 0.6-0.8

lead, cadmium, mercury and copper. Table 4 compares the results with the National Health and Medical Research Councils standard for edible fish4. As can be seen, the heavy metal concentrations are well below the NHMRC standard. Further details of the land disposal scheme are given in the papers by McKie and Clementss5.

A unique ecosystem has developed in and around this lake with a large number of water birds. Surveys by the Royal Ornithologists Union over the past one and a half years have revealed over 30 species of birds, including a sighting of the rare species, the Baillon’s Crake, in the annual 1991 survey.

Soil testing s5 has shown that the soil quality of the irrigated pasture is not significantly different from the non-irrigated pasture. Over 130 sheep keep the grass short to minimize the risk of grass fires, one of which razed the grassland in 1968 before the sheep were introduced.

Conclusion

Continuing improvements have led to significant reduction in waste generated from both the older high pressure polyethylene process and the new low pressure polyethylene process. The new process produces significantly fewer wastes and uses less energy and less water than the older high pressure process. The net effect has been a major reduction in wastes per unit of production basis.

COMPOL’s water management program has led to a reduction in water consumption and the introduction of a successful water recycling plan. 70% of wastewater is recycled to the manufacturing plant and the rest is used for irrigation, enabling zero discharge off site of treated wastewater, an excellent example of cleaner production.

References

Stauffacher, J.W. and Sheard, W.G. ‘Environmental Perform- ance and Product Uniformity of the Unipol Gas Phase Reactor System’, Society of Plastics Engineers, 1991 Environmental Protection (Prescribed Waste) Regulations, Victoria, 1987 McKie, C.J. and Clements, J.W. ‘Treated Wastewater and Disposal to Land at a Petrochemical Plant’ Australian Water and Wastewater Association, 1990 NHMRC, Food Standard AlZMetals Contaminants in Food, 1991 McKie, C.J., Clements, J.W. and Gaskell, N. Proc. Eighteenth Australian, Chemical Engineering Conference, Auckland, 1990, pp 509-516


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Cleaner production: an industrial example