INCINERATION OF HAZARDOUS WASTES

T. GANNON, A.R. ANSBRO*, and R.P. BURNS Glaxochem Limited, Ulverston, U.K.

(Received November 1990) Abstract. Glaxo has practiced incineration of liquid and gaseous wastes for over twenty years and currently operate elevenliquid and gas incineratorsin the United Kingdomand Singapore.The liquid incineratorsburn, as their main streams, those solvents that cannot be recovered and recycled within the processes. The early installations were for readily combustiblesolvents only. However,there has been a progressive move into the destruction of more difficult and hazardous wastes, with the consequential requirements for more sophisticated technology,in the beliefthat the responsibledestruction of waste should be tackled near to its source. The eventual aim is to be self-sufficientin this area of waste management. The incineration of hazardous liquid and gaseous waste has presented a seriesof design,operational and monitoringproblemsinto account which have all been successfullyovercome. The solutions take into account the environmental consequences of the operations from both liquid and gaseous emissions. In order to ensure minimal environmental impact and safe operation the best practicable technology is employed. Environmental assessment forms part of the process development and permitting procedures.

1. Introduction Glaxochem Ltd. a n d Glaxochem (Pte) Ltd. are the major primary bulk m a n u f a c t u r i n g companies of the Glaxo Group. Primary manufacturing capacity is largely centered in the U K a n d Singapore from where the active ingredients for the range of Glaxo products is circulated worldwide. Most of the expertise in the disposal of waste liquors is in the UK. Not all of these waste liquors are hazardous but most are organic in nature a n d at the least have a high oxygen demand. The approach of Glaxochem to this p r o b l e m is primarily that of waste minimisation. T o this end, liquid wastes pass through rigorous solvent recovery operations to ensure m a x i m u m recovery and recycling of solvents. The resulting residual liquid streams from these operations are either acceptable aqueous wastes or are significantly reduced in volume. It is this residual waste which must then be incinerated. To illustrate the effect of the recovery operations, Glaxochem at Ulverston currently receives 17 tankers of solvent per week with 2.5 tankers of waste leaving site. W i t h o u t the recycle operations these figures would rise to 146 tankers in and 315 tankers out. Even though the recycle operations significantly reduce the n u m b e r of tankers on the road there is still a risk of spillage or accident. With 2.5 tankers of waste per week this risk is felt to be unacceptable. It is C o m p a n y policy, therefore, to be self-sufficient in the destruction of hazardous liquid wastes in order to handle the problem at source. In achieving this target, the installed equipment will produce emissions within the statutory requirements. Glaxochem * Plenary speaker. Environmental Monitoring and Assessment 19: 105-125, 1991. 9 1991Kluwer Academic Publishers. Printed in the Netherlands.

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have been operating liquid and gaseous incinerators for more than 20 years. During this period, a variety of incinerator types have been employed to achieve the required destruction of waste. Incineration is used to destroy liquid and gaseous wastes that cannot be disposed of satisfactorily by other means. Typically the gaseous wastes are at low concentration in air streams but are highly odorous or in some other form present a nuisance value. The liquid wastes are primarily the streams remaining after operations to recover solvents and consist of still residues and solvent mixtures that are not amenable to current recovery techniques. Throughout more than 20 years' experience, the constraints on incinerator operation, particularly with respect to emissions, have become more stringent. At the same time the liquid mixtures requiring incineration have become more complex and difficult to handle. These constraints have been offset by an increasing understanding of the incineration process and by improved ability to detect the possible products of partial or incomplete incineration. All of these factors have had an influence on the design of incineration systems, allowing a more exact specification of the incineration problem and the equipment available for its solution.

2. H~tory Glaxochem began liquid waste incineration in earnest in the late 1960s with incinerators of the type shown diagrammatically in Figure 1. This type of incinerator is very simple and has no downstream processing of the combustion gases. It is therefore restricted to the incineration of hydrocarbon mixtures without organic sulphur, nitrogen and halides and containing little or no dissolved solids. Two of these incinerators were installed, one at the Montrose factory and one at the Ulverston factory.

SIeck 60m

W~$te G88 S t r e a m In

Combustion Chsrnber

I.D Fsn

I Fig. 1. Montrose incinerator 1980.

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Of these, only the Ulverston incinerator is still in operation, burning around 1 million litres of waste solvent per year. The limitations of this type of incinerator prompted the design of a more sophisticated incineration system at Montrose in 1974. This installation is shown diagrammatically in Figure 2. The design of this unit attempted to accommodate all the anticipated problems and requirements for a general purpose incinerator and incorporated the following features: (a) small horizontal combustion chamber, for ease of maintenance; (b) vertical downflow oxidation chamber, to handle molten solids; (c) an evaporator, for contaminated water; (d) waste heat boiler, to recover some of the energy released by the incineration process; (e) air pollution control equipment, to remove suspended solids and scrub acid gases. Post commisioning the unit has given 14-15 years of satisfactory operation. The fourth Glaxochem liquid incinerator was installed at the Annan factory in 1978 and the design is as shown in Figure 3. As can be seen this is a much simpler design than the Montrose unit, with incineration followed by exhaust gas conditioning. Post commissioning this unit has performed very satisfactorily for 10-11 years. Two waste gas incinerators were installed at Montrose in 1980, primarily for the destruction of mercaptans produced in the chemical synthesis of ranitidine. They are of the basic type shown in Figure 1 but the units can also burn clean solvents as fuel, as well as solvent-contaminated water. These two units carry out a single duty, with one on line Aqueous Waste

J

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Venturl throat)

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Fig. 2. Montroseincinerator 1974.

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S~ck

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vA .....

Oxidation Chamber

~__

Separator

x

/

DJlu, llon Air

Combustion Chamber

I--

VenturI Tan k

__

J

Fig. 3, Annan incinerator 1978.

and one as standby. In 1989 a third unit of this type was installed as the synthesis process was expanded. The Singapore factory has installed three process-dedicated incinerators which have exactly the same design and duty as those in Montrose. In 1989 a fifth liquid incinerator was installed at Montrose (Figure 4) primarily to replace that installed in 1974. As can be seen this is a simpler design than the 1974 unit, but retains the dowfire for solvents contaminated with solids. This unit has been brought on line recently. The 1974 unit is to be refurbished as a standby unit. There is a sixth liquid incinerator being planned for the Ulverston factory, which will be in operation in 1992 and will incorporate all that we have learned in 20 years of plant design and operation.

3. Operations and Operating Experience 3.1. PHILOSOPHY Incinerators within Glaxochem are operated in two ways. If the incinerator is dedicated to the destruction of waste material from a single process, then it is classified as part of that process and is controlled and operated by process staff. If the incinerator is for general use, destroying waste materials from a range of sources, then it is classified as a service and is operated by engineering department staff. This approach is adopted because the dedicated process incinerators receive a consistent feed stock at a readily defined rate and storage of waste gases is not practicable. The plant, therefore can be designed to closely match the production operations. This minimises the need for blending facilities for the waste

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Fig. 4. Montroseincinerator 1989.

material and generally results in smaller units and low levels of waste storage. The incinerators do, however, have to be reliable and/or duplicated. This is demonstrated by the gas incinerators at Montrose which are small and arranged so that every precaution is taken to prevent an incinerator failure interrupting production. The induced draught fans have attached flywheels to keep them turning in a power failure and they are also backed-up by an emergency generator. In the event of flame failure on one unit, the standby is ready to take over the duty quickly. The general purpose incinerators tend to be larger and incinerator failure is covered by providing adequate storage for waste material and designing the incinerator such that it is not operating at full capacity except when there is a need to clear a backlog of waste. The Annan incinerator, which is a dedicated process incinerator, operates on this second principle and, as a result, does not operate continuously. The general purpose incinerators are major capital installations. As these units are not dedicated to specific processes, the feed stock to the incinerator will vary in terms of calorific value and dissolved solids as well as organic sulphur, nitrogen and chlorine; feed stock management is a major concern. The incinerator staff must know what they are burning if satisfactory operation is to be maintained. The incineration conditions vary from unit to unit. The original incinerators operated at about 800~ with extremely short residence times. This temperature was subsequently raised to around 900~ to prevent cyanide formation and the Ulverston unit still operates at this temperature. The 1974 Montrose general purpose incinerator followed a similar pattern, being designed at 800~ but with the temperature of operation raised to 925~ The residence time in the oxidation zone is 1 second. The new Montrose unit runs at

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1000~ with a residence time in the oxidation zone of 1.5 seconds. Both these units have short flames. The Annan incinerator is required to burn large quantities of solvents containing organic halides and was designed to run at a temperature of 1250~ with a residence time of 1 second. At the time of the Annan installation, the value of a short flame incinerator was not fully appreciated and the flame in this unit is not particularly short. Support fuel for the incinerators varies from heavy fuel oil through gas oil to clean solvents, with heavy fuel oil being the dirtiest support material. The sulphur content of this material can be significant with respect to the downstream processing plant. 3.2.

COMMISSIONING COMMENTS

The commissioning of the various incinerators within Glaxochem has been of variable duration, largely due to the varying complexity of the incinerators themselves. As would be expected, the very simple liquid incinerators and gas incinerators commissioned quickly and relatively easily. The first complex incinerator at Montrose took up to 2 years to commission. This was largely due to its complexity and its being at the forefront of the technology available at the time. The Annan liquid incinerator and the latest Montrose unit took about 12 months each to commission. In the Annan case, this was due mainly to a shortage of liquors for incineration, while for Montrose the problem was adapting to the ever-tightening legislation and recommendations covering incinerator operations.

4. Design Considerations 4.1. PLANT LAYOUT The practical knowledge gained by Glaxochem is drawn both from the routine operations of the equipment and from the various commissioning exercises. While much of this can be classified as 'common sense' these comments are usually made with hindsight. As a method of highlighting this information, the design of the proposed waste liquid incinerator for Ulverston will be considered. The basic layout for this incinerator is shown in Figure 5. A key feature is the modular design of the plant. Each item of equipment is self-contained with connections between the units by ductwork and pipework. This approach is new to Glaxochem. The increased cost of providing an expandable plant is justified by the need; to secure good combustion, to efficiently treat the resulting waste gases, to maintain flexibility of feed stocks and to meet increasingly stringent legal requirements. This approach allows extra pieces of equipment to be installed and scrubbing systems to be easily upgraded as and when appropriate. 4.2. MATERIALS OF CONSTRUCTION The materials of construction for the various parts of the plant are being chosen carefully to deal with the anticipated corrosion/erosion problems. In this context, it is not

INCINERATION

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q !

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Chamber Oxldat~on

Stack

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~

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DilutION Fan Air

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L5 Fig. 5. Ulverstonincinerator 1992.

necessarily the use of exotic alloys that comes into consideration, but the fabrication quality of these materials. For example, in our experience the use of spiral wound and seam welded pipework and ductwork for the process streams is an unwise choice. The 1974 Montrose incinerator was constructed using spiral wound carbon steel items which rapidly failed in service. Replacement with higher quality seamless carbon steel items resulted in satisfactory operating life. The use of exotic allloys is not a guarantee that corrosion problems will be excluded even if laboratory corrosion tests suggest that the chosen material is satisfactory. For example, the quench down-comer on the latest Montrose unit is fabricated from Hastelloy C276. This has given one year's service and is unmarked. On the 1974 unit, the original venturi scrubber was a Hastelloy C276 variable throat device which lasted only a few weeks before suffering severe corrosion although the venturi might be anticipated as being in a less testing environment than the quench tube. Glass flake lined carbon steel andplastic venturis have been found to have satisfactory lives on this duty. In Comparison, the Hastelloy C276 venturi on the Annan incinerator has suffered no corrosive attack at all. The main corrosion effects seen at Annan are with the induced draught fan and on the hot crossover duct from the oxidation chamber to the quench system. The fan is of particular concern where the use of 316 stainless steel has been ineffective due to stress corrosion on the back side of the impeller. Experience shows the requirement for exotic materials of construction is limited and that lined carbon steel and plastics are more than adequate for most oft_he duties. In the light of this information, the Ulverston incineration plant will be constructed largely from lined carbon steel and reinforced plastic. The sole use of exotic alloy will be in the quench down-comer which is fabricated from Hastelloy C276. The potentially hot services will be

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in carbon steel with the cool service in reinforced plastic. The only worry in using plastics is the meltdown possibility if the quench system fails. The Glaxochem quench systems will be backed up in the event of failure to allow a routine system shutdown. One of the major concerns over carbon steel as a material of construction for the incinerator is the potential for external corrosion. Figure 6 shows the susceptibility of carbon steel to corrosion with respect to temperature and from this it is obviously desirable to have a skin temperature of 230~ At this temperature keeping an external paint cover is difficult and rain onto the hot surface can be a significant problem. One possible solution to this problem is lagging but this is not favoured by Glaxochem as it delays the identification of hot spots from thin or cracked refractory and could result in the occurrence of major damage. At Annan the problem is accepted and the incinerator is located in the open with all the resultant maintenance. At Montrose the incinerator was covered by a canopy and whilst this kept rain off, it provided ideal housing for local birds. As a result the new incinerator at Montrose and the proposed unit for Ulverston will be within an enclosed structure.

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ELECTRICHEMICp,L CORROIlON CORROSION RATE

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Fig. 6. Corrosion rate.

4.3. REFRACTORIES The Ulverston incinerator will be lined with high density alumina refractory bricks. This type of brick refractory has been found to be satisfactory at both Montrose and Annan. Both of these incinerators were originally lined with castable refractory and this failed rapidly in both units. During the process of finding satisfactory refractories, Montrose had more severe problems than Annan, suffering from eutectic formation on several occasions with

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subsequent refractory run off. A eutectic system in this context is a mixture of inorganic salts which in combination has a much reduced melt temperature. This is illustrated in Figure 7 for the combination sodium chloride sodium sulphate, and sodium carbonate. Annan's main problem was spalling of the surface due to the regular heat up and cool down cycle with no eutectic formation being experienced. Not surprisingly, therefore, the two units are lined with bricks of different specification. The Ulverston unit will follow the Montrose selection as there is a worry about eutectic formation with the inorganic solids likely to be in the waste stream to this incinerator.

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2 - Na2SO 4 - Na2CO3.

4.4. COMBUSTIONAND OXIDATION The high probability of inorganic solids in the feed stream to the Ulverston unit suggests that, as with the latest Montrose unit, the combustion and oxidation chambers should be arranged for downflow operation. The 1974 Montrose unit has the oxidation chamber arranged for downflow and molten salts flow satisfactorily down the walls of the chamber to dissolve in the quench vessel. Some problems have been experienced with choking of the throat between the oxidation chamber and the quench vessel but these have been overcome by smoothing the flow path of the glaze into the water. Experience has also shown that this area of high thermal shock is the area of most frequent failure of the lining with subsequent corrosion of the vessel skin. An easily removable sacrificial section is designed here to allow for quick and easy maintenance. It may be noted that this downflow pattern is not necessary at Annan where there are few dissolved inorganic solids and the upflow oxidation chamber does not glaze, nor is there significant accumulation of debris in the bottom of the chamber. Control over the feed is excercised by process dedicated storage tanks. The reason for a downfired combustion chamber is perhaps not as obvious but is equally logical. The ideal conditions to establish are very high initial turbulence with very

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good atomisation and then plug flow in the oxidation zone with minimal back mixing. This plug flow approach is to ensure that as much of the material as possible passing through the oxidation zone is subject to a residence time of 2 seconds whilst the size of the plant is minimised. A well mixed oxidation chamber, the total opposite of plug flow, would need to be physically bigger to achieve an equivalent residence time and even then statistically some material would have very low residence times. In practice the oxidation chamber of the unit will be between these two extremes, but careful consideration of the flow patterns can ensure closeness to one ideal or the other. The stated intention is to aim towards the ideal of plug flow in the oxidation chamber. Minimum disturbance to the gas stream is only achieved with a vertical downfired combustion chamber and a sloped transition piece between the combustion and oxidation chambers. A stepped transition would cause eddy formation in the traistion zone and disturb the flow patterns as would turning the gas flow between the combustion and oxidation chambers. This feature can be emphasised by some of the problems experienced with the 1974 Montrose unit which had a horizontal combustion chamber from which the hot gases had to turn through 90 ~ downwards. When burning waste organic liquors containing large quantities of dissolved solids or if organic silica was present then the eddy behind the transition resulted in a build up of deposits on the outside of the combustion chamber wall (Figure 8). This, plus deposition within the combustion chamber itself, diverted the flame onto the roof of the oxidation chamber with rapid destruction of the refractory. It is also

,~efroctor y Erros/oP

L_

waste Solvent

O o m b u s t i o n Air

Fig. 8. Montroseincinerator 1974.

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noteworthy that the refractory on the side of the oxidation chamber facing the combustion chamber is also a vulnerable zone as the gas stream is turned. The vulnerability of the refractory is largely due to the level of inorganic solids in the feed. In their absence, as at Annan, the turning of the flame, in this case upwards, creates no additional problems from impingement. Typically, on both units the refractory life is about 3 years and about one third is replaced each year. As final comments on the incineration zone, the new Ulverston unit will have injection guns that are very simple in design to reduce the risk of blockage and they will be easily removable on line. The aqueous waste for incineration will be introduced at the top of the oxidation chamber to control the oxidation temperature to between 1100 and 1200~ Air will not be used to moderate the oxidation temperature because of the unfavourable effect on the halogen/hydrogen halide ratio, the hydrogenhalide being the desired product of combustion of any organic halides. 4.5. QUENCH ZONE In the case of Ulverston the quench zone will again follow the approach of Montrose and consist of a series of watersprays and a wall wash leading down to a chamber through which the combustion gases bubble. Excess water from the quench plot flows to the separator associated with solid/gas scrubbing. The quench pot provides a reservoir of water to help cooling the combustion gases. Three problems have been experienced with this type of quench mechanism. These are: (a) a narrow inlet throat blocking with flowing salts, (b) undersizing of the drain line such that the liquid level could not be controlled under reduced firing conditions (c) the omission of a saw tooth weir on the bottom of the quench tube. This final point resulted in significant pulsations in the oxidation chamber resulting in increased back mixing. 4.6. AIR POLLUTIONCONTROL EQUIPMENT Downstream of the quench pot the solids and the acid gas load of the combustion gases must be removed before they are passed to the atmosphere. At the present time, the proposed Ulverston unit has a venturi scrubber for the purpose of solid scrubbing. To be efficient these units require a high pressure drop and must be fitted with a variable throat. Experience at Montrose indicates that corrosion of variable throat designs is unacceptably high and has also demonstrated a rapid drop in efficiency as the unit is turned down. Efforts to find a satisfactory alternative have not yet been fruitful. As well as removing solids the venturi scrubber removes significant quantities of acid gas but unfortunately not to acceptable levels. Downstream of the venturi scrubber there will thus be a standard packed gas scrubbing column. The scrubbing liquor in all units is sodium hydroxide solution to ensure good scrubbing of hydrogen chloride and sulphur oxides. Nitrogen oxides cannot be removed efficiently by this approach and, without

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further treatment plant, care must be taken to minimise the generation of these components. At the present time the waste liquors do not contain a significant quantity of organic nitrogen and the incineration conditions do not promote the formation of the oxides. However, the modular construction of the Ulverston facility will allow easy retrofitting of extra waste gas treatment if required. Glaxochem have not experienced any problems with the gas scrubbing towers. In fact there is a tendancy for suppliers to overdesign these. 4.7. PLUME SUPPRESSION The final step of the process is to exhaust the scrubbed combustion gases to atmosphere. In order to minimise the visual impacts Glaxochem has installed steam plume suppression equipment on all the liquid incinerators. This works well in general and no stack problems have occurred. The final treatment step in all the systems, however, is a direct contact condensing system. In the case of Annan this is carried out in the acid scrubbing system. This direct condensation liquor is then recycled via a cooling tower. Historically, this has been a standard direct contact cooling tower but it has been noticed that occasionally it is possible to form hypohalites in these systems which decompose on the cooling tower with a characteristic odour. As a consequence, the proposed Ulverston unit will be an indirect contact cooling tower to ensure no smell problems from this source. 4.8.

WASTE HEAT RECOVERY

Incineration operations generally generate a great deal of high grade energy in relation to their volumetric throughput. The question of whether this energy can be utilised is a difficult question to answer simply. Within Glaxochem waste heat recovery is not considered to be a viable option. To be effective the gas stream going to the heat recovery system needs to be low in solids. With the type of waste requiring incineration at the Glaxochem sites, dissolved solids are a major constituent. The new Ulverston incinerator will experience this problem with sticky residues blinding the heat transfer surface and being very difficult to remove. A solution to this problem is to pre-evaporate the feed stock leaving the solids behind. Experience shows this is not a particularly simple option. The waste liquors are frequently very corrosive which makes selection of materials of construction very difficult. Also experienced at Montrose with direct fired evaporation showed that the variation of the liquors was such that conditions within the evaporator were very difficult to control. These variations caused instabilities in the incinerator operations. There is one other major aspect to waste heat recovery and that is how it fits into the general factory energy system. In the Montrose case the steam generated from waste heat was only a very small portion of the total steam load and blending it into the general supply proved difficult. The waste heat system was neither reliable nor consistent. This would also be the case at Ulverston. Also for reliability all the steam generating plant should be under control of one group and there is a significant risk of conflict between the demands for incineration and for steam generation.

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WASTES

4.9. INSTRUMENTATIONAND MONITORING The new Ulverston incinerator will follow the latest Montrose incinerator which is controlled by modern stand-alone instrumentation with the plant largely under the control of the operators. Facilities are provided for continuous monitoring of temperature, flow, excess oxygen, particulates, carbon monoxide, sulphur oxides, nitrogen oxides, hydrogen chloride and chlorine. The differential pressure over the venturi scrubber is also monitored. Sampling facilities are installed for twice yearly checks for dioxins and heavy metals. At Ulverston, liquid discharges will also be checked routinely for dioxin content. The liquid effluent will pass, after neutralisation, to the factory effluent system. With all incinerators there is a small amount of inert solid waste disposed to landfill, during shutdowns. This will consist of slag and used refractory. 4.10. GENERAL CONSIDERATIONS Finally, regarding this section, there are one or two general comments on experience. The minimisation of plant size was discussed in terms of back mixing in the oxidation chamber and the use of a short highly turbulent flame in the combustion chamber. The difference between short and long flames can be clearly seen in Figure 9 where the long flame takes longer to achieve the desired temperature. In this situation 'long time' is directly related to 'large size'. Added to this is the effect of longer times in hot zones, which tends to increase the quantity of nitrogen fixed as the oxides, particularly if oxygen levels

SHORT

FLAME

.... ; ;-S MDE-;2 ;-E, ;i

LONG

FLAME

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.

CE

AVERAGE INCINERATION TEMP

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t

FLAME ZONE MIXING ZONE

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, ~HOTzoNEGAS

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are high. This latter point is another reason for not using air to temper the oxidation temperature. As with all practical systems, however, there is a downside to short flames. To achieve the desired flame length very high-energy atomisation is necessary to produce very small droplets. As the size of the atomised droplet is reduced so is the size of precipitated inorganic salt particles. The smaller the solid particles the more difficult the solids scrubbing becomes. The incineration systems tend towards forced draught to protect the fans from corrosive environments and to provide enough driving force for the solids scrubbing. In a downfired system under pressure there is a significant tendency to get a backflow of hot gases through the air system on power failure and fan stop. The advantages of a flywheel to maintain an airflow in this situation should be considered.

5. Environmental Impact Glaxochem's Environmental Protection Policy places upon individual factories the responsibility for the safe and acceptable disposal of wastes generated during their operations. This policy is an integral part of the overall business policy and strategy of the Company. It includes the safeguarding of human life and ensuring minimum impact on the environment. In this context compliance with regulatory standards are accepted as a minimum to be achieved. The Company recognises and implements its duty of care for its waste from the cradle to the grave.

INCaNERATORS MONTROSE 3 GAS 2 LqQUID

NTROSE

ANNAN 1 LLQULD

dLVERSTON I LIQU!D

ULvERSTO~

Fig. 10.

G l a x o c h e m U K sites.

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5.1. LEGAL REQUIREMENTS In the UK statutory powers for environmental protection are broadly divided into development controls, exercised through the planning legislation prior to the installation of plant, and direct pollution control.

5.1.1. Development Controls The principle legal requirement under this heading is to obtain the approval of the planning authority. To achieve this permission it is necessary to undertake an Environmental Impact Assessment (EIA) and submit an Environmental Statement in accordance with the Town and Country Planning (Assessment of Environmental Effects) Regulations 1988. this document forms part of the application for planning permission and is open to public scrutiny and comment.

5.1.2. Direct Controls Currently, direct legal instruments for pollution control employ a discrete single media approach, i.e. specific controls on discharges or emissions to air, water or land. New legislation due to be enacted during 1990 in the form of the Environmental Protection Act, however, will change this to a process-based cross-media regime of integrated pollution control. 5.2. EMISSIONSTO THE ATMOPSHERE In the UK, control of emissions to the atmosphere is exercised under the terms of the Health and Safety at Work Act 1974 and the subordinate regulations, Health and Safety (Emissions into the Atmosphere) Regulations 1983 and Control of Industrial Air Pollution (Registration of Works) Regulations 1989. The enforcing authoritities are Her Majesty's Inspectorate of Pollution in England and Wales and Her Majesty's Industrial Pollution Inspectorate in Scotland. 5.3. DISCHARGES TO THE AQUATIC ENVIRONMENT Discharges of effluent to controlled waters come under the jurisdiction of the National Rivers Authority in England and Wales and the local River Purification Board in Scotland. The Water Act 1989 and the Control of Pollution Act 1974 allow the discharge of effluent under conditions of a consent which specifies limits on the quantity and quality of the effluent. The limits are set on the basis of defined standards for certain priority substances categorised by European Economic Community (EEC) Directives as List 1 or Black List substances. Limits are also derived from Environment Quality Standards (EQS) which are based upon the defined Environmental Quality Objective (EQO) set for that particular water, e.g. Shellfish water, Bathing water. 5.4. DISPOSAL OF WASTE TO LAND The deposit of waste on land is controlled by the local authorities in the UK under the terms of the Control of Pollution Act 1974. This requires the transport of waste and the

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practice of waste disposal operations to be conducted in accordance with a licence which imposes conditions. This system will undergo radical improvement under the new law. 5.5. ENVIRONMENTALIMPACT ASSESSMENT- ULVERSTON As part of its procedures, the Company conducts environmental assessments (EA) on any new or modified process or product. With the advent of appropriate legislation formal EAs have to be submitted with planning applications. In the case of hazardous waste incineration these are mandatory. As part of the project to replace the Ulverston solvent incinerator, a detailed EA has been conducted. Possible environmental implications of the development have been fully investigated. Air dispersion studies based on a Gaussian model indicate that worst case ground level concentrations of waste gases will be insignificant and, in every case, at least an order of magnitude below the limits and guidelines recommended by the World Health Organisation and the European Community. Furthermore, the predicted levels are below those quoted in the scientific literature as likely to cause damage to vegetation. Effluent arising as a residue from the gas cleaning system will be discharged to a newly constructed site effluent system. No detectable impact is predicted and this will be verified by monitoring of the environment likely to be affected and compared with established baselines. Small amounts of inert solid will be removed periodically from the incinerator as part of the routine maintenance operations. These will be deposited in a local secure landfill site. Noise levels will be controlled by careful design and equipment selection. Surveys of noise levels at the factory boundaries are conducted on a regular basis and provide a suitable background for identification and remediation of any unexpected impact. 5.5.1. Air Dispersion Model Ground level concentrations of HC1, NOx, particulates, SO2 and C12 were calculated for the 40 m stack using a standard Gaussian plume dispersion model [1 ]. The model requires information on the wind speed at plume height and downwind distance values for the plume. The Briggs relationship [2] was used to relate the plume to atmospheric stability as classified using the Pasquill-Turner-Gifford scheme [ 1]. The effective height of plume was determined by flue gas conditions (temperature, efflux velocity and stack diameter). Plume rise was estimated using Holland's equation [3] assuming an ambient air temperature of 15~ and air pressure of 1013mb. Ground level pollutant concentrations were calculated for 360 points on a circular array centered on the proposed stack position. The grid points were spaced at 100 m to 1 km intervals and subsequently at 1 km intervals along radii 10~ apart. Concentrations were calculated for each of the 36 sectors and for grid points up to 90 ~ for each plume centreline. For each wind direction the source strength was weighted according to the fraction of time that the wind was in that sector for each windspeed class and stability class. The results are presented as contour maps of annual average concentrations, an

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PREDICTED

CONCENTRATIONS (•g

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POLLUTANT

121

WASTES

m -3 )

Sulphur Dioxide.

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example is given in Figure 11. Short-term concentrations will exceed these values and some monthly averages will be higher, whilst others will be lower, reflecting changes in meteorology. Annual averages provide the most appropriate form of data to compare with environmental quality standards.

5.5. 2. Results of Modelling Studies Predicted maximum long term annual average concentrations for various pollutants is shown in Table I. The major areas of impact are due east and due west of the site at approximately 600-700 m. EC Directive (80/779/EEC) gives limit values for ground level concentrations for smoke, SO2 dand N O 2. The relevant limit value for SO2 is 120 #g m -3. In the unlikely event of an increase in smoke concentrations (UK concentrations are declining), the limit for SO2 would be 80 ~g m 3. The predicted annual maximum incremental increase of 0.17 ~g m 3for SO2 will have a negligible impact on existing SO2 levels and will still be well within the EC limit. The same is true for smoke (suspended particulates). Compliance with the Directive ensures levels will not be detrimental to health. Using the six-month average of 21.4 / l m -3 for N O 2 measured by Warren Spring Laboratory, the predicted 98 and 50 percent values are 51.4 and 19.9 ~g m -s, respectively. These levels are below both the recommended EC Directive limit and guide values. The predicted long-term average will be a very small increment to background concentrations. There are no UK or EC ambient air quality standards for HC1 and C12. In such situations, the common practice is to tak the occupational exposure standard (OES) [4] divided by 40 allowing for an increased exposure time for the general public (time 4) and a large margin of safety (times 10). An even more conservative limit would be the OEL divided by 100. There are no available ambient HC1 or C12data for the Ulverston area, and very few for anywhere in the UK. Therefore, direct comparison of the impact of predicted HC1 and C12 levels on existing air quality is difficult. Compared to OEL/40 and OEL/100 values, the predicted levels are extremely low. Although no data are available for C12, HC1 concentrations of 0.5-2.0 #g m -3 [5] have been recorded in the north east Essex area. Predicted long-term HCI averages would appear to have an insignificant impact on existing air quality. Short-term concentrations can be indicative of worst case conditions. These conditions TABLE

I

Long term predicted pollutant concentrations.

Pollutant

Concentration

SO~ NO,

0.16 0.20

- 0.18 - 0.23

HCI

0.085 - 0.095

CI 2 Particulates

0.0045 0.043 - 0.048

ug m 3

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TABLE I1 Occupation exposure standards (gg m 3). Pollutant

OES

OES/40

OES/100

HCI CI,

700 3000

175 75

70 30

may be due to plant operational conditions or prevailing meteorological conditions. Both may contribute to elevated ground level concentrations of pollutants. Although long-term averages are useful in the context of air quality guidelines, an evaluation of short-term assessments giving rise to sudden elevated concentrations will identify detrimental impacts to human health, fauna and flora. Calculations indicated that incremental maximum ground level concentrations, even under worst case meteorological conditions still remain minimal. Dispersion coefficients are based on ten minute averages. As is to be expected, the short-term predictions gave concentrations which are greater than the long-term results. Limit values provided in EC Directives are based upon long-term averages. Comparison of short-term modelling data with EC values is therefore invalid. Comparison with The World Health Organisation (WHO) guidelines [8] is more appropriate. The W H O short guidelines for NO2, SO2 and SO2 and particulate matter are: 400/~g NO2m-3 for 1 hour and 150/~g NO2m-3 for 24 hours. 500 ~z7 SO2m -3 for 10 minutes and 350#g $02 m-3 for 1 hour. 125 #g SO2 m 3/125/~g particulates m -3 for 24 hours. It can be seen that the short-term predicted levels are unlikely to have significant impact on existing air quality. There are no W H O guidelines for HCI or C12. However, comparison with OESs shows that the levels are again extremely low. Although the incremental predicted levels are very low when viewed against existing air quality levels and health standards, it is important that their significance is also assessed with respect to population exposure, and flora and fauna.

5.5.3. Population Exposure The predicted incremental levels when compared to EC and W H O air quality directives and standards and existing air quality data indicate that levels will not be detrimental to human health. The impact area has the lowest population density in the Ulverston area.

5. 5. 4. Flora and Fauna The Ulverston factory is surrounded by Sites of Special Scientific Interest (SSSI) as classified by the Nature Conservancy Council (NCC). Of these, the most important is Morecambe Bay. Definitive literature on the effects of air pollution on vegetation is limited. The levels of

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the pollutants predicted by the air dispersion model are well below those known to cause injury to plants. Morecambe Bay is an estuarine complex of international significance for wintering wading birds and of national significance for wintering wildfowl. Incremental levels are unlikely to be detrimental to bird populations. Indeed the study identified various species that have formed habitats in the immediate vicinity of the factory. The Bay also supports a diverse terrestrial fauna including various beetles, weevil, moth, hoverfly and butterflies. The predicted incremental levels will have an insignificant effect on fauna.

5.5.5. VisualImpact It is unlikely that the main incinerator building will be seen outside the factory. Indeed it will contribute to improving the existing visual quality of the factory site area. The building will be screened from residential areas to the south and east by the Slag Bank and the existing factory buildings, and to the north and west by the site works and the storage tanks. Extensive planting of indigenious shrub and three species by Glaxochem will also help to screen the factory. 5.6. COMPLIANCE WITH LEGISLATION

All Glaxochem incinerators have complied with their relevant legislative permits. In over twenty years of incineration practice there have been no adverse environmental effects observed as a result of these operations. 6. Conclusions

Twenty-one years of operating waste liquid incinerators in Glaxochem leads to the conclusion that it is a safe and satisfactory method of destroying this type of waste. The increasing knowledge about the interaction of waste and the environment, however, shows that whilst incineration may be a useful tool both in terms of destruction of hazardous liquids and in terms of waste volume reduction, it is only viable if the products of the incineration are themselves harmless to the environment. It is in this area where the increasing knowledge is reflected in increasingly tight limits on what can leave the operation as acceptable waste. In order to meet the requirements of waste destruction, the apparently simple process of incineration must be treated as a major processing step requiring sophisticated technology, not an addition at the end of the operations. It should receive the same degree of attention and expertise as any other operation on site with respect to materials of construction, process design and engineering, instrumentation and control, and robust operability. Due to the need for flexibility, particularly with general purpose facilities, modular construction is advisable. References Turner, B.: 1970, Handbook of Atmospheric Dispersion Estimates, US Public Health Service Publication 99-AP26, USPHS, Cincinnatti.

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2. Briggs, G.: 1974, Environmental Research Laboratories, Air Research Atmospheric Turbulence and Diffusion Laboratory, 1973 Annual Report, US Atomic Energy Commission Report ATDL-106, NOAA, Washington DC. 3. Holland, J.Z.: 1953, A Meteorological Survey of the Oak Bridge area, Atomic Energy Comm., Report ORO-99, Washington DC. 4. Health and Safety Executive: 1989, Occupational Exposure Limits 1989, Guidance Note EH40/89, HMSO, London. 5. Sturges, W.T. and Hamilton, R. M.: 1989, Atmospheric Environment 23(9). 6. Williams, M. L.: 1988, An Assessment of the UK Position with respect to the 1987 WHO Air Quality Guidelines, Warren Spring Laboratory, Stevenage, Report LR650 (AP) January.