8. Waste treatment
Appropriate measures for waste treatment.
The following measures apply to all processes and operations.
1. You must not receive waste if you do not have enough capacity to store and treat it in line with your design criteria.
2. For all stages of the process, you must manage the waste to make sure the process is stable and to minimise the risk of:
- over-heating
- re-heating
- foaming
- uncontrolled biological activity
- leachate breakout
3. Waste treatment must have a clear and defined benefit and result in a fully recovered material. You must fully understand, monitor and optimise the waste treatment process to make sure that you treat waste effectively and efficiently. The treated output must be suitable for its intended use.
4. You must identify risks and characterise emissions from the process and take appropriate measures to control them at source or abate them.
5. You must have accurate and up-to-date written details of your treatment activities and process controls. The complexity of the waste you treat and the processes on site will determine the level of detail. You should include:
- information about the control system philosophy and how the control system incorporates environmental monitoring information
- simple process flow sheets that show the origin of emissions
- process instrumentation diagrams
- process flow diagrams (schematics) for waste, water and air and gas flow
- descriptions of process integrated techniques and waste water or waste gas treatment at source including their performances
- an equipment inventory, detailing plant type and design parameters, for example, time, temperature, pressure
- details of chemical reactions and the rate of reaction and energy balance
- venting and emergency relief provisions
- operating and maintenance procedures
6. You must use material flow analysis to identify potential contaminants in waste inputs, outputs and emissions; in particular where you accept packaged or bespoke waste streams.
7. You must ensure you fully understand the fate of any contaminants to make sure that you minimise, remove and recover them from the process.
You may need pre-treatment methods to minimise the carry-over of contaminants through to the treatment process.
8. You must not dilute undesired materials into the recycling or product cycle.
9. You must not proceed with the treatment if your material flow analysis indicates that losses from a process will cause:
- a breach of an Environmental Quality Standard or your permit
- a breach of a benchmark
- a significant environmental impact
- an issue in using the end material beneficially
10. You must clearly define the objectives and reaction (chemical, physical or biological) steps for each treatment process. You must define the end point to the process so that you can monitor and control the reaction.
11. You must define the suitable inputs to the process, and the design must consider the likely variables expected within the waste stream.
12. You must sample and analyse the waste to check that you have reached an adequate end point.
13. You must manage the pre-treatment of waste and biological treatment activities in a way that minimises the risk of pollution from:
- odour
- bioaerosols
- dusts
- other emissions
14. You must use plant and equipment that you can contain to minimise fugitive emissions.
The following measures apply to all processes and operations.
1. You must assess the likelihood of abnormal operating conditions. You must make sure you continue to comply with permit conditions by taking steps to prevent, alert and mitigate these events. Abnormal operating conditions include:
- unexpected releases or loss of containment
- start up
- unplanned stoppages and breakdowns
- shutdown
The following measures apply to all processes and operations.
Pre-treatment may include one or more of the following:
- hand-sorting
- de-packaging
- removing contaminants, for example using screening, separation, sifting, pressing or floatation
- mixing and blending – to obtain correct carbon to nitrogen or substrate characteristic ratios
- screening and thickening, for example adding polymers
- using additives, for example trace elements
- optimising particle size, for example using shredding or maceration
1. You must make sure you carry out particle size reduction where required:
- by the animal by-products regulations for sanitisation or pasteurisation
- to optimise substrate characteristics for effective and efficient processing
2. You must make sure that particle size reduction does not simply result in smaller contaminants entering the biological treatment process.
3. You must also:
- apply the correct technology to pre-treat the waste to provide optimal substrate characteristics
- retain the correct biological conditions to biodegrade the feedstock into an output that meets expectations and is suitable for its intended end use
- comply with additional regulatory requirements, for example, animal by-products regulations
4. You must carry out the pre-treatment of putrescible wastes in a suitably designed building. This must have an air ventilation and extraction system designed to make sure you comply with any associated emission limit in your permit. The ventilation and extraction system must be connected to an appropriately engineered air abatement system or gas recovery plant. Putrescible wastes include odorous wastes, ammonia-rich wastes and wastes containing animal by-products.
You can apply a risk-based approach when designing air containment for the pre-treatment of agricultural wastes only.
5. You must demonstrate that all process equipment is made of materials suitable for use and is being used according to its design capability and the manufacturers’ design life.
6. A qualified and competent person must justify and verify the use of operating plant and equipment beyond its design life, to demonstrate there is no additional risk of failure.
7. You must remove all non-compostable plastic and other contaminants in the feedstock, or reduce them to levels that are as low as reasonably practicable.
8. You must not rely solely on post-treatment technology to remove known contaminants. Where you use hammer mills to treat packaged waste you must take additional measures to make sure that you remove non-compostable or digestible plastics before or during the process.
9. You must take measures to remove any remaining non-compostable or digestible contaminants from the final material.
10. You must be able to demonstrate the removal technology is effective at removing contaminants.
11. You must consider your pre-treatment requirements at the design stage. Pre-treatment methods must give you the flexibility you need to process the types of feedstock you plan to accept at the facility.
12. Pre-treating waste feedstock may be done off-site from a treatment facility but there must be a process to ensure that feedstock is of a high quality.
1. You must install and operate a manual or automatic monitoring system that supports effective operational management and minimises operational difficulties. For example by displaying (visually and audibly) early warning signals to prevent system failures.
2. You must calibrate monitoring equipment and maintain your plant and equipment in line with manufacturers’ recommendations and your maintenance and inspection programme. This includes, for example, doing daily and weekly inspection checks and holding records of completion.
The following measures apply to all processes and operations.
1. You must segregate and condition the waste inputs before biological treatment. This may include:
- using shredders for opening bags
- using metal separators to extract undesirable components that might obstruct later processes
- using sieves or shredders to optimise particle size and segregate biodegradable fractions
- using air separation to segregate high calorific materials such as textiles, plastics and paper
- homogenising materials
- sterilising waste in an autoclave – before mechanical treatment
The following measures only apply to aerobic treatment.
An aerobic treatment waste facility may include the following processes (or combination of processes):
- in vessel composting (including rotating drum systems, containers and vertical towers)
- open-air windrow composting (animal by-products excluded)
- hall (housed) composting
- static aeration
- bio drying and bio stabilisation (MBT)
- thermophilic aerobic digestion (TAD)
- aerated lagoons and activated sludge (for waste water treatment)
Vessels used for batch processing of solid waste (for example in vessel composting or bio stabilisation for MBT) must be able to carry out continuous, representative temperature monitoring during sanitisation. You must link monitoring to an alarm system that you can check remotely and that gives a remote alarm notification.
To improve environmental performance and reduce emissions to air, you must monitor and control the main waste and process parameters, including:
- waste input characteristics (for example, C to N ratio, particle size, pH, porosity)
- temperature and moisture content (at different points if in a windrow)
- aeration (for example, through windrow turning frequency, O2 and CO2 concentrations, air stream temperatures for forced aeration)
- for windrow composting, the height and width of composting piles
- a visual and olfactory assessment of the material, to detect actinomycetes, fly infestation and odours
You can monitor the moisture content for enclosed processes before loading the waste into the enclosed composting stage. You can adjust it when the waste exits the enclosed composting stage, or when you move it from stage 1 to 2 to meet the requirements of the animal by-products regulations.
1. You must maintain optimal parameters to these ranges:
- pH 5.5 to 8.0
- particle size 10mm to 50mm
- temperature 55oC to 70oC (reducing after sanitisation and during stabilisation and maturation)
- moisture 60% to 65% (start of the process), 30% to 65% (during the process)
- carbon to nitrogen ratio 20:1 to 40:1
These ranges are advised optimal parameters. If you operate outside these ranges, you must justify your reasons and demonstrate there is no adverse impact on the treatment process or the environment as a result.
Temperature and moisture
2. You must monitor moisture and temperature during both treatment and storage and adjust the moisture in dry periods to prevent dusty conditions. You must keep records of monitoring data.
3. As a minimum you must monitor daily the temperature of composting waste during sanitisation and stabilisation. This can reduce to weekly during maturation if you can demonstrate the material is stable.
4. You must install continuous monitoring where it is required in your permit or under the animal and by-products regulations (such as for catering and food waste).
5. You must locate your monitoring points so they give representative data. If you insert monitoring probes into windrows and static piles you must first work out what length of probe you will need to get representative data, based on the size of the waste pile.
6. You must get data from within the core of the pile. For example, for a 4m stack you will need a probe that is over 2m long to make sure you can take a representative sample of the core temperature. Longer windrows will require more monitoring points.
7. You must control moisture using visual control and one of the following methods, a:
- squeeze or fist test (when carried out by an experienced operator)
- moisture monitoring device with read-out or connectivity to a data capture system
- an accurate oven-drying method
8. You must periodically validate your monitoring methods, for example, by drying if you rely on squeeze tests. You must keep records of your validation tests.
If you use portable aeration pipework you must clean it after each treatment batch.
9. You must assess all the monitoring data you collect to make sure you have a continually effective and stable process and that you can:
- take action and make safe and informed processing adjustments where needed
- minimise operational difficulties
- prevent creating anaerobic conditions
10. You must minimise oxygen deficiency and avoid anaerobic conditions occurring during the composting process.
11. You should take measures against excessive moisture in the waste by:
- adding input materials with high carbon to nitrogen ratio
- balancing the mix of materials and maximising porosity
- making sure windrows are appropriately structured and the construction allows for passive drainage and temperature convection
- placing oversized material at the base of the windrow
12. You must keep a record of:
- your temperature and moisture assessments
- the watering date and the origin of water used, for example composting liquor or roof water
Sanitisation and stabilisation periods
13. You must clearly segregate composting batches undergoing sanitisation, stabilisation or maturation.
14. You must clearly label batches to allow traceability from the receipt of the waste to its despatch from site.
15. You must not combine multiple stabilising or maturing waste piles or windrows into single larger piles that could result in:
- the inability to carry out representative monitoring and safe handling
- increased fugitive emissions, odour or over-heating
- anaerobic conditions developing
The Environment Agency does not consider lock composting or deep clamp systems to be an appropriate measure because they do not allow adequate monitoring or process control.
Leachate and liquors
16. You must stop composting liquors from pooling at the base of waste piles and windrows. You can do this by:
- installing sloping ground infrastructure and appropriate drainage
- regular cleaning
- minimising over-watering
17. To minimise the risk of cross contamination, you must keep the run-off from composting liquors separate from sanitising and stabilising waste if you want to reuse liquor on stabilising waste.
18. You must not use liquor drained from waste in sanitisation and reception areas on stabilising or maturing waste.
The following measures only apply to open air composting.
1. To minimise dust, odour and bioaerosol fugitive emissions to air from open air composting processes, you must:
- actively manage material to prevent anaerobic conditions developing and to prevent overheating
- prevent dry and dusty conditions occurring
2. You must work out the appropriate dimensions of your windrows taking account of:
- waste type
- heat generation and loss
- space availability
- effective retention time
- aeration requirements
- monitoring capability
- seasonal variation
3. You must provide enough space between composting windrows so that:
- there is sufficient passive aeration
- plant and equipment can access the windrows without compacting the waste or causing cross-contamination
4. You must adapt your operations to the meteorological conditions. For example, by:
- avoiding turning waste, screening or shredding during adverse weather conditions
- orientating windrows so that the smallest possible area of composting mass is exposed to the prevailing wind
- locating windrows and piles at the lowest elevation within the overall site layout
5. You must:
- maintain adequate moisture and control high temperatures to prevent anaerobic conditions, bioaerosols and odour plume dispersal
- dampen roadways and working areas
6. You must also consider using one or a combination of the following techniques where bioaerosols, dust or odour are a problem:
- cover actively composting windrows using semi-permeable membranes (particularly if there is an increased risk to receptors) – using alternative targeted containment may be acceptable
- use purpose made windrow turners
- use dust and bioaerosols suppressants during turning, shredding and screening, for example, back actor water sprayers or aprons on plant
- install static aeration with an aeration system that is the correct size to deliver enough air to the waste to prevent anaerobic conditions developing
Static-pile aeration
7. You must design your aeration system to cope with differences in feedstock and the demands of the treatment process. The system must be able to treat emissions from the process.
Positive or forced aeration is not considered by the Environment Agency to be an appropriate measure to control fugitive emissions. Forced aerated piles should be additionally covered with semi-permeable membranes to prevent fugitive emissions.
Negative aeration means drawing air down through the waste into the base of the waste and provides improved control and opportunity to treat emission.
8. You must remix statically aerated composting waste periodically to prevent preferential pathways developing. Your procedures must minimise emissions during this activity.
Remixing static piles is not usually a routine operation if the windrows and aeration systems are maintained and the windrow is well-constructed.
The following measures only apply to in vessel and enclosed systems.
1. Batch operated treatment vessels must have localised air control and extraction systems.
2. An in vessel batch system must incorporate air extraction above the loading and unloading doors. This minimises the emissions released when the doors are opened, directing them to appropriate abatement.
3. You must regularly inspect and maintain your aeration and exhaust system to make sure it remains fit for purpose, this means it is both:
- free from debris
- functioning correctly at all times in line with designed performance specifications
The following measures only apply to mechanical and biological treatment (MBT) and mechanical heat treatment (MHT).
1. You must characterise your process air and gas stream inventory and manage and treat it to reduce emissions.
2. You must only recirculate waste air with a low pollutant content in the biological process.
3. You may need to condense the water vapour contained in the waste air gas before reuse. In this case, cooling is necessary. Recirculate the condensed water when possible or treat it before discharge.
4. You must treat air from negatively aerated piles and enclosed systems with an appropriately designed and engineered air abatement system. The design must treat the maximum air flow and the full range of chemical contaminants and bioaerosols the exhaust air may contain.
The following measures only apply to AD and TAD plants.
1. The anaerobic treatment of waste may include a combination of multiple and complex activities. You must ensure these are listed in your permit.
2. You must identify and define all operational parameters and limits in your management system.
Digester stability
3. To reduce emissions to air and to improve the overall environmental performance, you must monitor manually or automatically to:
- make sure digesters are stable
- minimise operational difficulties
- provide sufficient early warning of system failures which may lead to containment failing and explosions
4. To demonstrate digester stability you must monitor and control the main waste and process parameters, including:
- pH and alkalinity of the digester feed
- temperature – continuously
- digester operating temperature
- hydraulic and organic loading rates of the digester feed
- concentration of volatile fatty acids (VFA) and ammonia within the digester and digestate
- biogas quantity, composition and pressure – continuously
- liquid and foam levels in the digester
5. You must define the optimum operating temperature depending on the digester’s biology and system design. You must keep the digester within the optimal operating temperatures and document this in your management system.
6. You must maintain a stable temperature in the digester preventing overheating and cooling.
You should consider insulating the digester.
7. You must understand the process parameters and make changes in the feedstock and micro-nutrient dosing to:
- maintain the digester to optimum performance
- be able to demonstrate maximised efficiencies for volatile solids reduction or chemical oxygen demand (COD) reduction in the substrate
8. You must install an alarm mechanism that is interlocked so that reactor feeding automatically stops when a gas pressure alarm condition occurs.
9. You must use Supervisory Control and Data Acquisition Equipment (SCADA) to monitor, record and display data for continuously monitored parameters.
10. You must carry out a daily visible inspection of your digesters using inspection ports.
11. Feeding systems installed inside buildings must have a hazardous gas warning system. You must consider these areas as part of your HAZOP and DSEAR risk assessment.
Preventing foaming and over topping tanks
12. You must take all measures to prevent and detect foaming by:
- actively managing the assessment and digester feeding rate
- monitoring the digestate stability
- fitting high level probes or sensors on tanks used for the treatment
13. If you use foam suppressants, you must have procedures in place to support their deployment.
14. If you use chemical additions, you must have appropriate controls and procedures in place for chemical storage, handling and use.
15. You must avoid decanting sacks or drums of chemicals directly into treatment tanks or vessels. You must monitor any reactions and make sure control mechanisms are in place to manage such reactions.
16. You must equip vessels and tanks used for liquid-based waste treatment, for example anaerobic and TAD digesters, with continuous temperature and level monitoring capability.
17. You must install pressure monitoring if there is a risk of pressurisation in the vessel.
18. You must link all monitoring to an alarm system that you can monitor remotely. The alarm system must give you an audible and remote alarm notification in the event of over or under-heating and over-filling.
19. You must install mixing systems to all liquid-based treatment vessels, these may include one (or a combination) of the following:
- mechanical stirrers using agitators
- hydraulic mixing using pumps that recirculate the substrate
- pneumatic mixing by recirculation (for example biogas in AD digesters)
20. Mixing or stirring mechanisms must be appropriate for the type of vessel used and the feedstock you are processing. This is to make sure there is:
- efficient mixing
- adequate oxygenation (TAD)
- uniform heat transfer
- sedimentation prevention
21. You must know the mixing efficiency and sediment loading in your vessels. Sediment must not impede mixing, which may lead to pressurisation or plant failure. You can demonstrate this by, for example:
- monitoring the agitation ampage of your mixing system
- using lithium tracing
- heat conduction thermal imaging
22. Tank design must:
- allow for sludge draw-off, debris and grit removal
- account for routine and expected pressure variations
23. You must also install pressure monitoring if there is a risk of over or under pressurisation in the vessel.
24. Vessels used for batch processing in solid waste systems (for example dry AD) must be able to carry out continuous temperature monitoring
The following measures only apply to AD plants.
1. You must manage gas production volumes within the processing constraints of the facility.
2. You must have contingency measures in place and appropriately manage any excess gas produced, including when there is limited gas to grid availability during low demand periods.
3. You must use measures such as decreasing loading rate and diverting feedstock if gas demand is compromised.
4. When determining gas storage capacity, you must consider how changes in climatic conditions, such as high temperatures in the summer, affect the volume of gas for storage.
5. You must protect your biogas upgrading and energy recovery plant with flame arrestors and slam shut valves.
6. You must install a permanent back-up generator to power critical plant and equipment in the event of power failure. Critical plant and equipment would include, for example:
- lighting
- maintain the integrity of gas storage systems
- flares for preventing plant failure and to manage health and safety risks
Leak detection and repair (LDAR)
7. You must implement a leak detection programme that identifies and controls methane slippage from all processes and storage on site.
8. Your procedures must make sure propane and odorants (for example mercaptans) are handled safely.
Combustion units
9. You must inspect and maintain all gas utilisation plant and equipment, as a minimum, following manufacturers’ recommendations. You must record all routine and non-routine inspection and maintenance.
10. Gas combustion stacks must be vertical and unimpeded by cowls or caps.
11. Stacks for releasing point source emissions must have an ‘effective stack height’ unless otherwise stated in your permit, for example, if you operate under a standard rules permit.
12. You must monitor emissions following the requirements in your permit.
13. You must submit a record of each combustion unit and fuel type yearly.
14. You must consider whether you can use the heat from processing or combustion.
Combustion plant – medium combustion plant, specified generators and boilers
The guidance medium combustion plant and specified generators: environmental permits has more information about complying with the medium combustion plant directive and specified generator regulations.
15. You must comply with the emission limits in your permit and you must use the relevant monitoring standards.
1. You must install pressure relief and vacuum relief valves (PVRVs) on all tanks where there is a risk of over or under pressurisation.
2. An appropriate qualified engineer must design the PVRVs and gas pipework fitted to your biogas storage vessels.
3. You must demonstrate that PVRVs are able to and can cope with the anticipated maximum gas production volumes and pressures to operate within the design of the plant.
4. For all tanks, pipes and vessels where PRVs are fitted the plant manufacturer must provide design pressures.
5. You must only use PVRVs designed, tested and manufactured in line with recognised standards such as BS EN ISO 28300:2008 or API2000.
6. You must design and monitor gas production rates and organic loading so the excess pressure in the tank does not exceed the ISO28300 or AP12000 certified leak test rate of the PVRV.
7. Pressure relief valves and gas pipe work must be able to cope with the anticipated maximum gas production volumes and pressures. Under the highest gas flow scenario, back pressure on tanks containing biogas must be less than the maximum allowable operating pressure and more than the minimum operating vacuum.
8. When determining pressure set points you must consider:
- that maximum operating pressure must be no higher than the certified leak test pressure
- the pipework dimensions
9. You must incorporate gas production rates in the calculated maximum flow rates for the following conditions:
- changes in temperature
- changes in atmospheric conditions
- safety requirements.
10. Valves must be set so that they do not produce fugitive emissions during normal tank pressure fluctuations.
11. You must fit pressure sensors to your digestion tanks and gas storage vessels. You must maintain safe operating pressure by managing gas production and directing biogas to:
- gas storage
- treatment
- utilisation plant
- flare
12. You must specify a maximum pressure for each digester above which there is no further feed to the digesters.
13. If excess gas pressure builds up in the tanks this must trigger an alarm which immediately instigates the venting systems.
You should locate pressure relief and vacuum devices independently from gas off-take lines and install stand-by valves to allow for down time during maintenance.
14. You must inspect, maintain and calibrate PRVs regularly and after foaming or over topping events. You must inspect and protect PVRVs against environmental and climatic conditions, for example by providing frost protection and barriers to prevent damage.
15. You must incorporate isolating valves so you can remove PVRVs from a live system for maintenance without producing large fugitive emissions or compromising site safety.
16. You must locate isolation valves before a fully bolted spool under PVRVs so they can be removed without affecting security of the isolating valve.
17. You must record the gas pressure.
18. Data logging on SCADA must be in place to record release events within operational pressure ranges. You must record the date, time and duration of the release. You must not make modifications to the PVRV without manufacturer’s approval or you will void the ATEX classification and you will not meet DSEAR Regulations.
19. You must record gas pressure events that are out of the expected operating range, including the date, time and duration of the pressure relief events.
PRVs inspection and calibration
20. You must correctly calculate the safety set point of PRVs. You must review these when there are changes to the operating process. You must then do any required adjustments.
21. A competent person must correctly set and fit each PVRV.
22. All PVRVs must be correctly maintained and inspected, following manufacturers’ recommendations. You must have an agreed, written scheme of examination in place for their inspection and maintenance.
23. You must be able to demonstrate that a qualified engineer checks PRV function, and caries out testing and maintenance.
24. You must give your personnel safe access to all PVRV’s.
25. The PRV manufacturer must provide the certified capacity flow curve of the PRV and demonstrate that the test was completed according to BS EN ISO28300 or API2000 on approved test apparatus.
26. Each PVRV must have a current functional test certificate based on BS EN ISO28300 or API2000 procedures for production testing. This certificate will include details of the retained pressure at specified flow rates. This figure must exceed 75% of the set point using calibrated and independent measurement technology.
27. The test certificate is valid for 3 years from the date of production or the previous test. You will need to get an earlier revalidation and certification if the following is evident or has occurred:
- maintenance inspections indicate that the contamination build up is excessive
- corrosion
- a foaming incident
- tank overfill
The following measures only apply to AD plants.
1. You must prevent the emission of uncontrolled release of biogas and biomethane.
2. You must inspect, maintain, routinely test and keep a record of all gas storage and treatment plant and equipment following the manufacturers’ recommendations or your inspection regime.
3. You must identify the intended end use of the biogas to determine the appropriate treatment method. You must consider the following factors:
- dewatering
- removing hydrogen sulphide which may corrode gas engines
- removing oxygen and nitrogen
- removing ammonia
- removing siloxanes, particularly from digesting sewage sludge
- removing particulates
- removing carbon dioxide particularly when upgrading from biogas to biomethane
- adding propane to improve calorific value for biomethane gas grid injection
4. You must assess hydrogen sulphide levels in the biogas to determine the efficiency of the removal methods applied. You should do this by monitoring gas quality before and after using gas cleaning equipment.
5. You must continuously monitor biogas flow, quality, pressure and composition. Monitoring systems must be interlocked where possible and have remote alarm capability.
6. You must remove water (condensate) from the biogas to protect the collection system, energy recovery plant and auxiliary flare. Condensate must be discharged into a contained drainage system or recirculated back into a digester. Condensate storage must not produce odorous emissions.
7. You must collect biogas from all digesters and all other treatment and storage vessels where methane is actively generated.
8. Biogas storage facilities must be gas tight, pressure-resistant, weather proof, and resistant to ultraviolet light and fluctuations in temperature.
9. You must not allow biogas and air to mix unless it is used for desulphurisation. If you use oxygen to desulphurise biogas you must automatically monitor oxygen levels. You must also use high-level alarms which are set to automatically stop adding air before the lower explosive limit is reached.
10. If you use carbon filters, for example to clean gas before combustion, you must use procedures that minimise the risk of exothermic reactions during their maintenance, for example, by purging with nitrogen. You must contain and treat purged gases.
Flares or surplus gas burners
11. You must install or have a gas flare available for use at all times. You must not routinely use flares or vent directly to the atmosphere.
12. You should use enclosed (ground) design flares on all new plants. They should be capable of achieving a minimum of 1,000oC with 0.3 seconds retention time at this temperature.
13. On existing sites where shrouded or open flare are installed you must make sure that gas can effectively combust to destroy trace elements.
14. You must make sure that the finish on the exterior of the flare is weatherproof as well as heat-resistant. The structure of the flare must be designed to withstand wind stresses.
15. You must protect ancillary items such as control and instrumentation equipment, including cabling. Providing housing makes maintenance tasks easier, but you must consider any explosion hazards.
16. You must minimise the operation of the flare and use it only for emergencies and during maintenance to protect the integrity of the plant (for example, during start-ups or shutdowns).
17. You must specify measures in your procedures to minimise flare use during routine maintenance. This includes, for example, to:
- reduce feed rates to lower gas production
- increase the safe storage of gas where capacity is available
- install stand-by gas utilisation plant
18. You must monitor and record the use of your flare. Your records must include the date, duration and number of flaring events.
19. Your SCADA systems must be able to continuously monitor gas flow and when the flare is activated.
20. You must be able to quantify emissions if required and identify any potential improvements that would reduce flaring events.
21. You must routinely measure other parameters, for example:
- composition of gas flow
- gas temperature
- ratio of assistance
- velocity
- purge gas flow rate
22. You must routinely measure pollutant emissions, for example:
- oxides of nitrogen (NOx)
- carbon monoxide (CO)
- VOCs
23. Monitoring and interlocking must be linked to your SCADA system.
24. Flares must be automatically activated when the quantity of biogas exceeds a set maximum limit and before venting of biogas occurs.
25. During commissioning, you should consider lean burn flares where gas quality is poor to prevent venting and pollution.
Flare noise
26. Flares can cause noise. This can come from the vents, the combustion process and smoke suppressant injection. You must design new flares to minimise noise emissions.
Noise avoidance can include the following measures:
- reducing or attenuating the high-frequency steam jet noise by using multi-port steam injectors – designing the orifice to cope with potential coke formation is essential
- installing the injectors in a way that allows the jet stream to interact and reduce the mixing noise
- increasing the efficiency of the suppressant with better and more responsive forms of control
- restricting the steam pressure to less than 0.7MPa gauge
- using a silencer around the steam injector as an acoustic shield for the injectors
- using enclosed ground flares