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ULAB Recycling Plant Design

Brian WilsonIndependent consultant Brian Wilson outlines the planning, design, financial considerations, and operating principles for a new used lead-acid battery (ULAB) recycling plant in low and middle income countries.

The growth of the green energy generation has opened a growth market for lead batteries as the storage medium of choice, based on price, life cycle and the fact that the batteries are easily recycled at the end of their working life. The growth in green energy generation is particularly prevalent in Asia1, where there are the world’s largest solar energy plants and Africa2 with plants in the top 10 of the world’s largest. 

This predicted growth in the market has raised concerns about the fate of these batteries at the end of life and specifically the environmental and occupational health performance of operators engaged in recycling in low and middle income countries. So, what should policy makers in these regions consider to ensure that effective and environmentally sound reverse logistics are developed that take lessons from the sustainable closed loop recycling seen in North America and Europe that contributes so much to the circular economy?

The first agenda item on the road map to environmentally-sound closed loop recycling will be a country-based feasibility study to ascertain lead battery use and consumption, used lead battery generation and an analysis of the import and export trade. The study should also include an analysis of the performance of existing used lead battery recycling plants and the current procedures relating to the export of used batteries. Only when a full picture of the existing lead battery value chain and trade analysis in a country is available can recycling plant investment decisions be made.

Sometimes, particularly in countries in economic transition, data acquisition is challenging, but the Basel Convention Secretariat has published a methodology3 to acquire and collate lead battery value chain data and when combined with information from the UN Comtrade4 database, it should be entirely possible to prepare a data set that can be used to base an investment decision. 

If the data set indicates that an environmentally sound lead battery recycling plant could be a feasible proposition, the next step is to prepare a business plan, complete with investment requirements and financial analysis for at least a ten-year projection. If the plan shows that the net present value (NPV) and the internal rate of return (IRR) on the initial investment are both positive, then consideration must be given to a detailed analysis of where to site the plant, how to operate it and what to include in the construction specifications.

The phrase NIMBY (not in my back yard) could not be more applicable than to a used lead battery recycling plant and so in order to avoid extensive public objections and endless planning applications, the question of site selection is a key procedure that should follow the site selection criteria suggested here:

  • Take account of any existing businesses or organisations, such as a hospital or a food processing plant that might be close to a suitable site
  • Note the previous or current use of the site to avoid building a smelter over an underground mine or an abandoned waste dump
  • Try to locate into an existing and designated Industrial Zone that has a protected cordon where private houses and schools cannot be built
  • In the absence of an Industrial Zone as an option, avoid selecting a Green Field site and try to locate a Brown Field site that is free from any legacy issues, such as a hazardous waste dump or ongoing litigation
  • Explore if it is an option to locate either at or adjacent to a lead battery manufacturing plant such that at least the environmental and health issues associated with lead will already have been dealt with
  • The surface area requirements are critical, but never underestimate how much space is required for current and future operations
  • Ascertain the utility and energy requirements and available fuel and utility supplies, because certain fuels, such as gas or oil may not be readily available, electricity if available, may not be reliable, and water supplies might be by road tanker only
  • Site access is important because used lead batteries and refined lead ingots are heavy, so roads need to be to a standard that affords trucks access without getting stuck in mud or damaging the suspension system
  • Be aware that certain “ideal” locations have fauna or flora sensitivities or features that cannot be disturbed, such as nesting sites or animal and bird migrating routes
  • Check to make sure that any prospective site is not located close to a ground water source or an aquafer used to supply drinking water. If a ground water source or aquifer is located, then distance downstream from the water course
  • Never build a lead smelter in a valley where fugitive emissions might be trapped for days under certain unfavourable weather conditions
  • Never build a lead smelter in a flood plain unless the site and access roads are above the flood plain
  • Make sure that the area selected is stable and not subject to seismic activity, such as earthquakes, sink holes, erosion, and volcanic eruptions
  • View any prospective site to ensure the surrounding topography will not lend itself to landslides, rock falls, avalanches, or rivulets following heavy rainfall
  • The climate, nationally and locally, because in certain countries seasonal weather systems can lead to severe rainstorms, hurricanes or typhoons, excessive heat or cold and sandstorms. It is also wise to check the prevailing wind conditions and directions for the past 12 months to ensure that any fugitive emissions are not carried to populated or agricultural areas

The site selection check list is long, but essential, and once the boxes have been checked and the site selection criteria agreed, the following procedure can be implemented: Fig 1: Site selection process

Once the site or area that meets all the conditions applicable to the selection criteria has been selected, then decisions must be made about renting or purchasing the land so that a second and more detailed financial assessment can be prepared.

However, before the final financial assessment can be prepared and finalised a site plan must be prepared together with a preliminary list of essential equipment for use on and off site, process and administration buildings, and material and product storage areas.

Whilst it is entirely possible for companies already engaged in used lead battery recycling to specify the equipment required, it is also advisable to solicit a number of quotations from turnkey companies that specialise in designing, fabricating, constructing and commissioning recycling plants as an insurance that nothing in the preparatory stages has been missed in the site selection process and that any advances in process technology are included in the tender document.

Nevertheless, there are process and site specifications that should be conditional for any prospective tender, but not always specified as the focus is on the technology and not the procedures. For example, to minimise congestion on site have a one-way traffic control system such that vehicles enter the site and do not exit by the same route. This also means that a vehicle wash can be installed at the exit to remove any lead product or material from the wheels and tyres thereby preventing Lead dust contaminating the surrounding roads.

Fig 2: Elevated ETP (Courtesy of Pb Metals S.A., Costa Rica)Plan for a closed loop, so that no process effluent is discharged from the site. Ensure that all process effluent drains to a central effluent treatment plant (ETP) for processing to a saleable product and any residual effluent is used to damp down the site or for cooling the ingots during casting. The ETP can be segregated to treat process effluent and surface water drainage separately. Capturing rainwater in arid regions is also a cost saving investment as water is required in the recycling processes. All areas subject to vehicle or pedestrian traffic must be concreted with surface water drainage to the ETP. If the chosen site is liable to flooding, then the ETP must be elevated (Fig 2) so that the treatment vessels and all the ancillary equipment is above the highest recorded flood level. In this way, contamination of the flood water with leaded waste is avoided.

All material entering the site must be inspected and either accounted for or in the case of the used batteries and process reagents, weighed. This means installing a roll on–roll off weigh bridge. In the case of used battery deliveries, the storage area must be under cover with an acid resistant impermeable resin coated floor capable of storing 1 ton lots of ULAB either palletised or in plastic containers taking the weight of fork trucks and delivery vehicles.

For those companies entering the ULAB recycling business for the first time, it is tempting to just install a battery saw, or even two battery saws, to break the batteries, but unless the quantities of used batteries are minimal, it is worth investing in a mechanical breaker for two reasons. Firstly, separation of the metallic grids and the battery paste, means that the grids can be processed through a melting furnace and the paste either smelted by campaigning through a single furnace or a twin furnace operation. Processing and refining the grids and the paste separately is considerably more energy efficient and reduces the refining time, because the paste furnace bullion is almost pure lead. The second reason for installing a mechanical breaker is that the time required to break batteries is also reduced.

Fig 3: Automated Battery Breaker (Courtesy of Green Recycling Industries, Nigeria, and STC, Italy)The battery breaker (Fig 3) must be a stainless steel automated hammer mill capable of breaking used lead batteries up to 50 kilos in weight at a rate of 15 tons an hour and with good and clean separation of the metallic grids, the lead oxide and sulfate paste, the electrolyte, the polypropylene or ABS battery case material and the separators. Furthermore, the breaker must have exhaust ventilation to remove the risk of acid mist contaminating the working areas and suitable soundproofing to meet the legal requirements for workplace noise levels.

Assuming that a mechanical breaker is selected for the new recycling plant, it must be housed in its own segregated area and have an impermeable concrete floor with any drainage running to the ETP. The layout of the plant should be such that the material ejected from the battery breaker is placed directly into suitable bunkers in the case of the grids and the paste, and woven bags in the case of the plastic case materials and separators.

If the tender does not include paste desulfurisation, and this will be largely a function of throughput, provision must be made to gravity dry the paste to 5% moisture content prior to charging to the furnace in order to minimise smelting time and reduce the risk of explosion if the paste is wet. However, if there is sufficient throughput to justify paste desulfurisation and vacuum filtration of the by-product, provision must be made for by-product treatment to produce a saleable product.

Fig 4: Charging an Enclosed and Ventilated Rotary Furnace (Courtesy of Sunlight Recycling, Greece, and Engitec, Italy)It also pays to prepare the furnace charges in advance and use a screw hopper to charge the furnace in seconds rather than minutes. However, the process must be either automated with exhaust ventilation to a baghouse or conducted in a totally enclosed building with exhaust ventilation to a baghouse and the charge moved to the furnace just prior to charging (Fig 4).

There are a number of proven competing pyrometallurgical recycling technologies available, and whilst it is not the purpose of this article to recommend any single technology, it is important to take into account a number of critical factors when selecting a furnace. It is important to:

  • Select a technology that can process grid metallics, battery paste, baghouse fume and refining drosses.
  • Ensure that the furnace has a dual fuel burner in case the preferred fuel is unavailable locally at any time.
  • Ensure that if a rotary furnace is selected, the burner is located at the rear of the furnace to minimise the risk of damage during charging, and to permit maintenance during charging or adjustments to be made during melting or smelting without risk to the operator or maintenance personnel.
  • Consider whether to install oxygen enrichment of the burner to reduce cycle times, fuel consumption, NOX gas emissions, and refractory wear.
  • Make sure that spare parts or IT support are available and in the case of an automated operation this is a vital consideration, especially if the site is located in an emerging economy and far away from any technical and engineering support. That being the case, a dual system must be installed so that if the automated computerised system fails, then the recycling operation can switch to a manual operation until the IT support arrives to restore the automated operation.

As is often the case, if the initial start-up plan incorporates one furnace, account should be taken of any projected increase in demand for new lead batteries and so it may well be prudent to include and commission the necessary civil work, that is piling and concreting, for a second furnace when the plant is under construction, rather than try to retro-fit all the work and the equipment in at a later date, with all the disruption to production that will inevitably result.

Photo 4. Baghouse configuration: (L to R) Cooling duct, drop out chambers, filter plant, scrubber and stack (Courtesy of Golden Swan, Equatorial Guinea)Control of atmospheric emissions is not only a legal requirement in virtually every country, but is a moral obligation for all those employed in the lead industry. However, all too often the baghouse ID (induced draught) fan selected does not produce adequate suction to cope with the exhaust ventilation demands of the furnace and refining operations. Ideally, the furnace operation should have two baghouses, one dedicated to the combustion off-gases and one to the hygiene ventilation required during charging, melting or smelting and tapping the furnace bullion. Whilst in certain operations with low throughputs the furnace hygiene baghouse is shared with the refining operation requirements, again ideally the refining operation should also have a dedicated baghouse, albeit this baghouse can be designed to service the combustion and hygiene requirements of the refining floor (Fig 5).

There are a variety of filtration media, such as ceramic filters, fabric filter bags and electrostatic precipitators, but the principles are the same, that is, the lead bearing process dust is captured by the filter medium to meet atmospheric emission discharge limits. Electrostatic precipitator plants can capture particles down to 0.1 microns, but they are expensive. If costs dictate that a fabric or ceramic filter plant is selected, it is most likely that a scrubbing tower will have to be installed between the baghouse exhaust and the discharge chimney stack to remove any residual traces of lead bearing dust and sulfur dioxide.

If ceramic or bag filter plants are selected it is essential that the fume produced in the furnace has sufficient time to agglomerate in the extraction ducts so that the particle size is sufficiently large enough to be captured by the filter medium. The length of the ducting will depend on the climate. The hotter the climate, the longer the ducting needs to be. It should be noted that it is illegal in many countries to introduce a cool air bleed into the duct to promote agglomeration as this practice also effectively reduces the concentration of leaded particles in the final atmospheric discharge.

When designing the flue system, and irrespective of the type of filter plant selected, the ideal velocity of the lead dust through the ducting is 22 metres per second5 to avoid the buildup of dust in the flue. Sharp bends should be avoided because leaded dusts tend to stick to the inside bends of the duct if the velocity falls below 22 metres per second, which can occur at points of acute bends. If drop-out chambers are installed in place of a sharp bend, consideration must be given to how the dust collected in the drop out chamber is to be removed. Best practice is to avoid installing drop out chambers. The baghouse dust should be collected in sealed drums that are charged directly to the furnace with the refining drosses to recover any lead. 

For bag type filter plants, spark arrestors must be installed at points in the ducts prior to the baghouse to prevent any embers from reaching the filter bags and burning holes in the bags, rendering them useless, or worse still, burning down the baghouse. Instrumentation, either manually operated or digital should be installed to check the pressure drop across the filtration medium to ensure that the cleaning cycle is effective and to flag when the bags need to be changed.

The workload of the baghouse can be reduced by enclosing the furnace operations and providing ventilated hoods on all the refining kettles, to improve extraction efficiency and working conditions. Depending on the quality of the housing and hooding, such measures will also reduce the electrical bill for operating the baghouse.

Slag produced during the furnace operations is classified as a hazardous waste and because disposal to a licensed hazardous waste dump is becoming increasingly expensive; consideration should be given to either rendering the slag inert, through charge optimisation6 or further processing, such as solvent extraction or conversion to a stable, non-leachable product such a paving slab that conforms to local building regulations and will only be used outdoors. Alternatively, and again this option will depend on the throughput, desulfurisation of the battery paste prior to smelting should be considered, because recent research suggests that the furnace slag and baghouse dust produced using desulfurised paste has a lower lead content than charges with non-desulfurised paste7. Furthermore, given a period of time to stabilise, the desulfurised slag can pass the TCLP test with results below the US-EPA recommended limit of 5ppm.

Fig 6: Covered and ventilated refining kettles (Courtesy of Wirtz Manufacturing)Refining kettles (Fig 6) should be elevated to permit gravity feed to the casting machine. The lips of the refining kettles should be one metre from the mezzanine floor to ensure that operators do not fall into a kettle.

All refining kettles must be covered with exhaust ventilated hoods that permit bullion blocks to be charged to the kettle without removing the hooding, and with fittings for mixers, de-drossing (auto or manual), alloy or reagent additions and sampling. Ideally there should be three refining kettles with one dedicated to produce pure lead to 99.97 or 99.99%, the second to produce grid metal alloys and the third as a standby to refine dross and dust bullion and to act as a spare in the event of any maintenance requirements to the pure lead and alloy kettles.

Fig 7: Lead casting, stamping, weighing and strapping machine (Courtesy of Lewis Australia)The casting process should be fully automated with measured mould filling, de-drossing (flame or scrape), stamping, stacking, and weighing. All lead ingots should be stored under cover in a secure building to await delivery to the customer or export (Fig 7).

On site laboratory testing of purchased used batteries, by products and refined lead ingots is essential and the laboratory should be under positive pressure from a HEPA filtered air supply with a double door entry system and no direct access to the operating areas.

Every effort should be made to provide the employees with a safe working environment with procedures designed to minimise occupational lead exposure. So, all personnel entering the operating areas must change out of their own clothes and into the appropriate work wear. The work wear will vary depending on the tasks and operations. The Clean and Plant side changing rooms will be segregated and designed so that when personnel return from the plant they must pass through the shower bays and wash basins before entering the Clean Changing area8.

If an onsite laundry is installed, the works clothing should be collected in water soluble plastic bags and loaded into the washing machines without opening the bags. The bags will dissolve at 60°Celsius and this system prevents any leaded dusts on the works clothing contaminating the laundry. Wash water from the laundry should be drained to the ETP.

If meals and refreshments are to be provided on site, then the canteen must be isolated from the operating areas with access only through a changing room fitted with washing facilities and a change of clothing. The canteen must be under positive pressure from a HEPA filtered air supply and a double door entry system.

Fig 8: Site plan showing the location of the Changing Rooms and CanteenThe changing rooms and canteen should be located on the perimeter of the site so that operators do not walk through the plant in clean clothes to enter either the changing rooms or the canteen. Similarly, the same principle applies to the security office and the administration buildings (Fig 8).

If possible, and this will sometimes depend in the selected site, orientate the buildings so that solar panels installed on the roofs will generate the maximum amount of green energy to supply power to the offices and ancillary services.

Finally, the buildings housing the lead smelting and refining operations should be enclosed and connected to a hygiene baghouse so that the buildings are under negative pressure, thereby minimising the risk of fugitive emissions being released to the atmosphere. 

References

  1. Bhadla Solar Park, India – 2.25 Gigawatts and is currently the world’s largest solar energy farm
  2. Benban in Egypt – 1.8 Gigawatts (4th largest)
  3. http://www.basel.int/Portals/4/download.aspx?d=UNEP-CHW.13-INF-22.English.pdf 
  4. https://comtrade.un.org/data/
  5. https://www.donaldson.com/en-us/industrial-dust-fume-mist/technical-articles/understanding-conveying-velocities-to-save-money-dust-collection/ 
  6. Lead acid battery recycling in Costa Rica (2012): A case study, G. Esquivel-Hernández, P. Bolaños-Ulloa, M. Navarro-Monge, R. Alfaro-Solís, J. P. Sibaja-Brenes, J. C. Mora-Barrantes, J. Valdés-González.
  7. Application of a Sulfur Removal Hydrometallurgical Process in a Lead-Acid Battery Recycling Plant in Costa Rica (2017); Marta Navarro-Monge, Germain Esquivel-Hernández, José Pablo Sibaja Brenes, José Carlos Mora-Barrantes, Ricardo Sánchez-Murillo, Juan Valdés-González, Pablo Bolaños-Ulloa
  8. Design of Changing Rooms and Washing facilities: https://ila-lead.org/UserFiles/ILA_GN_Changing_V05.pdf
 

 

Year of publication: 
2020
Wordcount: 
3,589