Singleton Birch Invest For The Future

Singleton Birch Ltd, based at Melton Ross in North Lincolnshire, are the UK’s largest independent lime producers. The company supply quick lime, hydrated lime and chalk products to a range of industries including iron and steel, construction, chemical and water treatment. They have recently invested over £3 million in a state-of-the-art crushing and screening plant for the production of limestone fines, predominantly for the large integrated steel-works owned by Corus in Scunthorpe. Richard Stansfield, production and landfill manager, reports.

Singleton Birch are lime producers with a history that dates back to 1815 when the company was first established in Manchester. Around 1830 William Singleton Birch joined the company and over the following years developed a mineral merchanting business serving the Manchester area; in 1875 he became the founder of W. Singleton Birch & Sons Ltd.

Around 1850, after the railway line was extended eastwards from Manchester via Sheffield and through to Grimsby, records show that William Singleton Birch was leasing land from the Earl of Yarborough at Chalk Hill, Melton Ross, for the purpose of quarrying and the manufacture of whiting. By the time he decided to pass on the ownership of the company to his two sons he had built up a considerable business, mainly in Lancashire, where he had developed warehousing and distribution centres based on rail and canal transportation.

The younger son, Thomas Henry Birch, carried on in charge of the company as majority shareholder until his death in 1919. It was Thomas Henry’s wish that the grandson of William Singleton Birch, Lionel Walker Birch Martin, should inherit his 95% shareholding. Although Lionel Martin was a director of the company, most of his time was spent on his first love, fast cars, and he gave his name to the legendary Aston Martin car. His autobiography references his quarrying interests in Lincolnshire helping to fund what started off as a hobby. He died in 1945 and his majority shareholding was passed to his second wife, Katherine Martin. Katherine died in 1958, leaving most of her shares in trust for the benefit of three charities — NSPCC, RSPCA and Barnados. This trust is still the majority shareholder in the company today.

Throughout the 1960s steel-making practices changed and shaft limekilns were introduced at Melton Ross to produce burnt lime products to replace the use of raw stone as a flux in the steel furnaces at Scunthorpe. The company’s first slaking plant was commissioned in 1965 to produce a high-calcium hydrated-lime powder. The shaft kilns were partially replaced in the early 1970s with two 300 tonnes/day gas-fired rotating hearth (calcimatic) kilns to meet the high quality and increased volumes demanded by the steelworks.

As a result of the fuel crisis in the late 1970s Singleton Birch constructed the first of their four 300 tonnes/day Maerz parallel-flow regenerative kilns. This type of kiln produces a good quality lime product using significantly less fuel. The four Maerz kilns at Melton Ross were commissioned in 1981, 1984, 1986 and 1996.

Significant capital investment has been made in the company’s processing capability at Melton Ross Quarries. Downstream from the kilns equipment has been installed to manufacture a wide range of lime products to meet customer requirements. There is a limited amount of associated storage available for each product and therefore sales/ production planning has become a key requirement, particularly when faced with fluctuating customer demand for burnt lime.

In the late 1990s the company realized an opportunity to continue the restoration of the quarry at Melton Ross through the landfilling of non-hazardous filter cake residues from titanium dioxide manufacturers located on the Humber Bank. Investment was made to develop a fully engineered landfill site to contain these filter cakes.

Today, the principal activity of the company is quarrying chalk with the associated manufacture, sale and distribution of lime and chalk products and landfill operations. The company operate three chalk quarries at Melton Ross, Mansgate and South Thoresby.

STONE PRODUCTION

The quarry at Melton Ross extracts over 1.6 million tonnes of chalk a year. The deposit forms part of the Northern Province Upper Cretaceous sequence, which is a hard, massively bedded chalk containing a small percentage of flint nodules.

Following overburden removal, 108mm blastholes are drilled using a Hausherr 55HD hydraulic drill rig. The explosive column consists of a single 0.5kg primer and two detonators at the bottom of the hole with the rest of the column charged with ANFO from a mini-mixer mounted on the back of an agricultural tractor.

Blasting normally occurs on a daily basis with a three- or four-hole blast yielding 4,000–5,000 tonnes of chalk. With saturation moisture content approaching 14% it is essential that the chalk is kept as dry as possible to avoid handling problems in the plant, hence the frequency of blasting.

The fragmented rock pile is then transferred to MMD semi-mobile primary and secondary crushing units using two 50-tonne wheel loaders, either Cat 988s or Volvo 330s. The top bed consists of a MMD 750 primary and a MMD 500 secondary, the bottom bed a 1000 and a 625, respectively.

The primary and secondary crushers reduce the product size to –150mm. This is conveyed at an average rate of 400 tonnes/h to a scalpings plant where two Hunt West screens separate out the –25mm fraction and the –50mm+25mm fraction. This material is conveyed to the new limestone fines plant.

The –150+50mm fraction is transferred to a conveyor and transported, via a tunnel, to the main processing plant situated on the other side of a public road. Here the material is further sized into 50–75mm, 75–100mm and 100–150mm fractions ready for burning in the limekilns.

NEW LIMESTONE FINES PLANT

The original limestone fines plant consisted of crushers and screens designed to produce a –3.35mm product that is used as a flux by Corus in their iron-making process. Singleton Birch have supplied the Scunthorpe steel-works with limestone fines for a number of years. The fines produced were from a plant based on old-technology hammer mills and conventional multi-deck sizers. Owing to the 2% flint content of the chalk and high moisture content, this was an arduous crushing job and wear-rate costs were high and efficiency low. Because of the moisture content of the chalk deck heating on the sizers was needed to prevent blinding of the meshes, which also required high maintenance.

It was decided in 2000 that with increasing demand from the customer a new plant would be necessary for the future that would allow increased production from a plant with less equipment, reduced maintenance costs, reduced power requirements, consistent grading and state-of-the-art safety and environmental features.

With this difficult brief the engineering and production team set about a complete review of what the latest developments in crushing, screening and feeding and general plant design could offer in the new millennium. Tests were carried out in the UK and other parts of the world before a decision was made to incorporate two REMco Star 500 vertical-shaft impactors at the heart of the new plant, working in tandem with screens and feeders made by Rhewum of Germany. Nottingham-based Conveyor Systems Ltd were selected to build the plant.

Feed material

The plant is fed with the two sizes of material from the quarry scalpings plant. The –25mm chalk is conveyed to a screen where the –3.35mm is separated out on to the product belt and conveyed straight to the store, while the oversize is conveyed to the mill feed hoppers. The –50mm+25mm material is fed directly into the mill feed hoppers and from here the –50mm+3.35mm chalk is fed, via Skako vibratory feeders, into the two REMco crushers, the feed rate being controlled by the mill’s motor current. The crushed material is then conveyed to two more screens, the oversize being recirculated to the mills and the undersize conveyed to storage. The material remains in a closed loop until all passes –3.35mm.

Crushing

Given the large differences between the chalk and the flint nodules, and the high moisture content of the chalk, REMco engineers, from their experience of making sand, recommended two Sandmax 500HP anvil machines with hydraulically lifted swing tops, each with the capacity to produce up to 150 tonnes/h of –3.35mm products when fed with an overall 50mm x 4mm feed in a closed circuit with the Rhewum screens. These two machines replace and are expected to ‰ produce more product than the four horizontal-shaft hammer mills previously used.

The cost of each of the REMco crushers has worked out similar to each of the old type of horizontal crushers, although only two are required to replace four machines. On this basis there has been a direct capital cost saving of 50% with further cost savings being achieved on the capital cost of the downstream structures, screens and conveyors.

On the old machines complete hammer changes were required on a weekly basis, whereas similar work is only required every sixth week on each REMco crusher, saving considerable labour and downtime. The cost of wear parts per tonne of product with the REMco units is proving to be less than one third of that of the old machines, while power consumption has been reduced by approximately 15%.

Screening

The main criterion when choosing the screening equipment was that the screens needed to consistently produce a –3.35mm product even when the material was moist and sticky. Rhewum (GB) Ltd carried out extensive on-site trials with a small WA-type screen and proved that, even with a moisture content of up 11%, the limestone could be screened efficiently and without any blinding.

Three Rhewum WAU 390 x 360/1 screens where installed, each handling 290 tonnes/h on a 3,900mm wide x 3,600mm long deck inclined at 38° and fitted with a 4mm aperture square mesh. To ensure an even spread of material over the screens, a SVWAU 3900 vibrating feeder supplies each unit. The screens are virtually maintenance free and only require 2.4kW of power per unit. The outer part of the screens and feeders is vibration free so all chute work is flange-bolted to give a dust-tight operating environment.

Storage and loading

The limestone fines product is delivered into the storage shed via a tripperconveyor in the roof of the building. Ultrasonic level probes are used to indicate when the fines heap reduces the required level and the tripper then automatically moves to its next position. The storage shed holds approximately 7,000 tonnes of product.

Lorries enter the building via a separate entrance where the floor of the building is approximately 2m lower than the main storage area. A Cat 972G wheel loader feeds the product into the lorries over a small wall, thus keeping the two vehicles apart. The height difference also allows the wheel loader driver better visibility into the back of the lorry.

The new plant was officially opened on 4 June 2004 by Corus’ chief operating officer.