Process Plant Technology designed and supplied two previous Evaporator Plants on this site. Evaporators 1 and 2 were installed in 1997 and 2003 respectively, both of which are still fully operational.

A new pre-concentrator plant will be installed to process the entire feed stream and to evaporate a further 50t/h water vapour and discharge the liquor into an insulated storage tank. The intermediate concentrate in this tank will then be fed to both of the existing evaporators. The overall feed liquor processing capacity will therefore be increased by approximately 25 – 30% which is in line with the client’s current expansion horizon and is the most cost and energy effective solution to provide this additional capacity.

The concentration of calcium lignosulphonate solution is complex as the solution is highly scaling and also releases SO₂ upon heating. A novel solution employed on the Concentrator is to utilise the acidic condensate produced from the evaporator as a descaling agent.

This new plant only achieves partial concentration which results in significant energy savings overall, realised through utilising a single, low compression MVR Fan.
Planned completion of the project is mid-2017.

In this instance, the client’s feed was a concentrated nickel sulphate catholyte stream. The feed also contained significant levels of impurities, such as iron, chlorides and free sulphuric acid. The crystalliser is operated under vacuum in order to produce the desired α-hexahydrate crystals.

The entire plant was constructed out of SAF2205 and titanium to resist the effect of chlorides at the low pH and high temperatures experienced in the plant. The crystals from the crystalliser are dried in a fluid bed dryer and the final product is bagged in 1 ton bags.

Special design features include a compact layout incorporating a single body forced circulation crystalliser, two off pusher centrifuges and a circular fluidised bed type dryer. The dryer off-gas scrubber comprises a two stage design to reduce final gas contamination levels to well within the desired specification.

Process Plant Technology were the successful bidders for the design and supply of equipment for a complete effluent treatment project in Chile. The aim of the project was to provide the customer with a sustainable, Zero Liquid Discharge (ZLD) effluent treatment program, producing solid mixed salt and sludge for disposal and clean process condensate for re-use within their process.

The pre-treatment section is required in order to remove metals and other impurities, leaving a mixed brine solution that can be evaporated to yield a mixed salt crystal. The cleaned liquor is fed to a single forced circulation crystalliser where crystals are formed by evaporating the solution, making a slurry from which the crystals are separated for disposal. The plant incorporates a two stage Mechanical Vapour Recompression (MVR) Fan set for energy efficiency. Hydrocyclones and screen-scroll centrifuges followed by screw conveyors complete the solids separation process.

The liquor is high in chloride ions necessitating the construction of equipment in corrosion resistant materials such as super duplex stainless steel, fibre-reinforced plastics (FRP) and titanium.

The customer in this instance was a major electricity provider with an ongoing contaminated water problem on all its power stations. Ash water is often concentrated using RO processes and the concentrate discharged for retention in the ash dams. This process has proven unsustainable and this particular pilot plant allows for experimentation on cooling and Eutectic Freeze Crystallisation of the brines. Testing allows the checking of tubular exchangers under limits of practical cooling down to -25°C and any intermediate temperature above this. The pilot plant is designed to be modular and may be moved between sites once it has been initially tested at the customer’s test centre.

The Freeze Crystalliser (FC) and Mixed Salt (MS) Crystallisers were supplied to a South African coal mine as the final step of a Zero Liquid Discharge (ZLD) system for their effluent evaporation ponds. The Freeze Crystalliser removes Glaubers Salt from a RO brine stream at very low temperature. The remaining liquor then undergoes further concentration by reverse osmosis prior to being combined with the Glaubers Salt crystals and fed to the mixed salt crystalliser, which produces final mixed salts for disposal and condensate for re-use.

The Glaubers Salt Crystalliser comprises a conventional surface cooled unit utilising refrigerant outside the cooler tubes which is carefully designed to prevent build-up on the process side of tubes. Large crystals are easily separated for disposal or re-combination with the process stream prior to MS crystallisation. The crystals are very clean and opportunities are being investigated to either sell or further process this commodity to a saleable anhydrous salt.

The mixed salt crystalliser consists of a single effect mechanical vapour recompression (MVR) forced circulation unit, with a two stage MVR Fan set used to recompress the vapour. The main crystalliser body and associated components are manufactured in FRP to reduce cost whilst maintaining excellent chemical resistance. A fine, damp mixed salt is generated for disposal using a screen-scroll centrifuge.

One of the additional key features is the modular design of the Plant; effectively built as nine skids which allowed the bulk of the installation to be executed off site as well as facilitating moving of the Plant to other future locations if required.

The Distillation Unit was designed for a local South African steel mill to treat the preheated enriched scrubbing liquor from existing H₂S and NH₃ Scrubbers by stripping with low pressure steam. The Enriched Ammonia Liquor is first stripped of H₂S in the Deacidifier column producing Lean Ammonia Liquor, a portion of which is recycled back to the existing H₂S Scrubber, the balance pumped to the new (second stage) Ammonia Distillation Column.

In the Ammonia Column the ‘Free’ ammonia compounds are first stripped in the upper section to generate Stripped Ammonia Water, a portion of which is recycled to the NH₃ Scrubbers. The balance of the Stripped Water overflows into the bottom section of the Ammonia Still where the ‘Fixed’ ammonia compounds are released using primarily caustic soda and then stripped using steam to produce clean waste water which is discharged from the plant.

Low pressure exhaust steam is used for the stripping process and is fed to the ammonia column and then the deacidifier. The vapour exiting the plant contains the H₂S, NH₃ and HCN vapour with some steam which is discharged for further treatment by the customer.

The CO₂ Capture and Utilities Infrastructure Plant was supplied to a South African chemicals producer to provide additional utilities infrastructure (including a water-tube boiler, cooling tower, process water and steam condensate storage) and to recover CO₂ gas from the new boiler flue gas for use in their existing chemical process. Some of the utilities are consumed within the CO₂ capture and utilities plant, with the balance being exported to the existing facility.

The upgrade project included additional storage capacity for steam condensate and process water, a new cooling tower capable of cooling 1500 m³/h cooling water with a total heat load of 20MW and a new gas-fired water-tube boiler with a maximum capacity rating of 37 t/h at 21 bar (g).

A novel amine-based CO₂ capture process from Shell Cansolv was utilised to capture the CO₂ from the boiler flue gas. This comprises post-combustion CO₂ capture technology by chemical absorption using a modified amine solvent as the absorbent. The outstanding feature of this technology is the high steam economy per ton of CO₂ produced.

The entire project was managed by PPTech from technology selection and customisation through process design, detailed design, construction and commissioning. This complex project was completed within a 22 month period on a complete LSTK contractual basis without a single reportable lost time injury throughout. The plant operates very well, meeting and or exceeding all capacity requirements and produces an exceptionally pure CO₂ product.

The crystalliser was supplied to a Brazilian Vanadium producer to recover sodium sulphate and a concentrated mother liquor stream (containing ammonium sulphate) for reuse in the vanadium extraction process.

The sodium sulphate MVR crystalliser is designed to process barren liquors derived after precipitation of ammonium metavanadate (AMV). The process is complicated by impurities associated with the vanadium process, in particular ammonium sulphate and sodium vanadate. In addition, the liquor contains chloride ions at a sufficient concentration to build up in the circuit, increasing corrosion rates at low pH. This necessitated the construction of equipment in corrosion resistant materials such as super duplex, high alloy materials and titanium. Crystals are formed through evaporation which are then separated for reuse in the vanadium extraction process. The plant consists of a single effect mechanical vapour recompression (MVR), forced circulation crystalliser. A two stage MVR Fan set is used to recompress the vapour which presents a durable, easily maintainable compression device for this remote location. Two parallel solids handling trains, each incorporating a hydrocyclone, screen-scroll centrifuge and a screw conveyor ensure high overall plant availability.

PPTech designed and supplied the client with two steam heated, falling film evaporators, operating under high vacuum to concentrate 76% ammonium nitrate up to 96% . These units more than double the existing liquid ammonium nitrate evaporation capacity at the customer’s site, and proves to be a more cost effective solution for this duty than the existing air swept unit. The evaporator set generates a stream of process condensate equivalent to the required evaporation rate, i.e. approximately 3t/h. There is no contaminated air plume (as associated with air swept units) and the only emission to atmosphere is a small steam discharge from the vacuum ejector.

Process Plant Technology designed and supplied equipment for a Falling Film (FF) evaporator with a mechanical vapour recompression system (MVR) which was installed to pre-concentrate the dilute sodium nitrate feed to a 25wt% solution. The bulk of the required evaporation takes place in this new FF evaporator, allowing the existing crystalliser to undertake the remaining evaporation and crystallise the solution. Slurry from the crystalliser is then processed through a new centrifuge, flash dryer, coating system and off-gas scrubber. An automated bagging unit packages the crystals into 25kg bags, which are manually palletised and stored.

Another existing plant, a triple effect evaporator / crystalliser, was modified and re-used to concentrate the dilute potassium nitrate feed to a 24wt% solution. The concentrated solution is purged to a new storage tank, loaded into tankers, and transported to a bottling plant at a separate location.

PPTech was also responsible for the design and supply of equipment associated with the modifications to the two existing crystallisers.

The aim of this project was to provide the client with a sustainable effluent treatment program, producing saleable sodium chloride and clean process condensate. The presence of high concentrations of calcium chloride within the lime treatment product stream precludes removal by crystallisation, and thus the calcium is removed from the evaporator feed stream in a two stage precipitation process. The solids from the circuit are recovered and washed on separate filter presses and disposed of as a soil additive. A triple effect forced circulation, sodium chloride crystalliser allows for treatment of 140Ml/annum clarified brine. The dewatered salt is bagged for subsequent out-loading by truck and transport off-site. In addition, a small, forced circulation mixed salt crystalliser is provided to process a contaminated purge from the salt crystalliser. This enables the generation of clean salt for sale.

The presence of corrosive organic acids complicated the plant design, necessitating the extensive use of rubber-lined steels, fibre reinforced plastics, titanium and Teflon lined piping. The project was undertaken on an EPC equipment supply basis with the customer employing their own EPCM contractor for overall project management.

One of Process Plant Technology’s main strengths is the design and construction of crystallisers in a variety of different applications. In this instance, the client’s feed was a dilute nickel sulphate stream from a leach filtration plant. The feed also contained significant levels of free acid.

The mandate was to minimize overall energy costs and the result was a falling film pre-concentrator followed by a Draft Tube Baffle (DTB) crystalliser operating under high vacuum in order to crystallise the desired hydrated crystal. The entire plant was constructed out of SAF2205 to resist the effect of chlorides at the low pH and high temperatures experienced on the plant. The crystals from the crystalliser are dried in a circular fluid bed dryer and the final product is bagged in 1 ton bags.

Special design features include a single body four stage falling film evaporator incorporating a single high lift MVR fan for high energy efficiency. Use of a DTB crystalliser enables the growth of larger crystals, improving dewatering, drying and final product quality.