The Hanson Ketton cement plant in Rutland, UK is the company’s main supplier of cement into the busy London and South East region of the UK. The plant was constructed in 1928 and began production in 1929. It has since undergone a series of expansions and upgrades, most recently with the installation of a Polysius kiln (No. 8) in 1986. Despite having to mothball its Kiln 7 in 2008 due to market conditions, the company continues to invest heavily in the plant, with major environmental, efficiency and quarry projects ongoing and planned for the coming years.
GC: Can you describe the history of production at the Ketton Works?
Stewart Jones, Plant Manager (SJ): The plant began production in July 1929 as the Ketton Portland Cement Company. Initially it had one small wet kiln, operating at around 0.05Mt/yr in 1930, the first full year of production. In 1933 Kiln 2 was installed and Kiln 3, installed in 1939, brought total production to around 0.23Mt/yr in the early 1940s. A further three wet kilns were added in 1954 (Kiln 4), 1962 (Kiln 5) and 1967 (Kiln 6), bringing production to around 0.65Mt/yr in the early 1970s.
However, it became clear by that time that the plant needed to invest in new technology or suffer the same fate as the many other UK plants that had already closed down. In 1973 plans were drawn up to install a large, modern FLSmidth dry process kiln, with preheater and planetary cooler. The early 1970s was a turbulent time economically, but Kiln 7 (0.5Mt/yr) finally came online in 1977. It helped to increase production to over 1Mt/yr in the mid 1980s, when a further significant investment came in the form of Kiln 8. It is a 1.3Mt/yr capacity Polysius line with precalciner and a grate cooler.
After 1986 the six wet kilns were all decommissioned and have since been removed from the site. Kiln 7 was mothballed in 2008 as the effects of the global economic crisis took hold. Kiln 8 is the only line in operation at the moment.
The plant has had various owners over the years, including Rio Tinto, RTZ Corporation, Scancem and, since 2002, HeidelbergCement. It carried Castle Cement branding between 1986 and 2009 but was changed to Hanson following the acquisition of the aggregates and concrete group by HeidelbergCement in 2007 and the subsequent consolidation of its cement business into Hanson UK.
GC: Please outline the production process used by Kiln 8.
SJ: The quarry is pretty unique here in that the mixture of limestone, clay, silica and iron-containing minerals is perfect for cement manufacturing. It is a shallow but very wide-ranging quarry, around 5km from end-to-end. Quite significant parts of it have now been returned to rural use, as per our restoration plan, and our solar power plant, which I will come onto later.
We extract around 1.8Mt/yr of material from it in total, which represents the vast bulk of raw materials that we need. The only things that we bring in are iron sludge, sourced as an alternative raw material from Anglian Water, and gypsum, which is brought in from British Gypsum’s Fauld mine, around 120km to the north west. We also use Cemset, which is made from recycled gypsum wallboard.
In the quarry we use a combination of track vehicles and dumper trucks to bring materials to the primary crusher, which is around half way between the furthest reaches of the quarry and the plant. It is a Krupp Hapra 3034/8 impact crusher that, when fitted with its 8 shafts and 72 hammers, weighs 96t. It has a 2700kW motor, operates at around 1700t/hr and reduces the material from as large as 2m to <45mm in a single pass. This then goes down a 1.1km belt conveyor to the covered mix beds, of which there are two. There is a 43,000t, 88m-diameter bed for ‘lime clay,’ a mixture of lower grade limestone and clay, plus silica and iron containing minerals. There is also a 10,000t, 53m-diameter bed for high quality (98 - 99% CaCO3) limestone. Each area of the quarry has undergone a detailed geological survey and there is a cross belt analyser on the conveyor, so we know the chemical composition of the material and can control it accordingly.
Raw material homogenisation continues in storage with a rotary conveyor and boom stacker using a continuous chevron stacking method. The material is taken via reclaimers (450t/hr for lime-clay, 250t/hr for limestone) to two 200t Besta buffer silos, which feed the raw mill as required. The proportions are controlled by an on-site analyst, who alters the feed rates depending on the blend required.
The raw mill is a Polysius RM46/23/85 vertical roller mill (4.6m table diameter), which provides 260t/hr of raw meal at 8% residue on 90microns. This goes to a 25,000t storage silo, prior to entering the preheater. We are quite ‘blessed’ in that we have such a large raw blend storage capacity. It allows for around 10 days of operation without needing to run the raw mill. When we had our annual maintenance in January 2017, we did a lot of work on the raw mill and we were able to bring it back online after the kiln came back online.
The pyroprocessing system comprises a two-string four stage Polysius Dopol type 2442 suspension pre-heater kiln with AS Precalciner, which has a combined centre stage. The kiln is 68m-long and 4.2m in diameter. It is inclined at 3° and has a clinker capacity of 2750t/day (0.9Mt/yr). This works out at a cement capacity of around 1.3Mt/yr.
The plant has a chlorine bypass that was installed by A TEC in 2006. It has a kiln gas capacity of approximately 8%.
The cooler is a Polysius Repol grate cooler of 3m x 30.3m. It was upgraded with a CemProTec Static Inlet in 2008. There are 10 cooling fans and the clinker leaves at typically 80°C above ambient temperature.
There is the capacity for 110,000t of clinker storage in a single silo. We extract it from underneath the silo from multiple points via a series of conveyors to the cement mill building, which houses two Polysius ball mills. Each of these can operate at up to 100 - 120t/hr.
GC: What changes have been made to the process in recent years?
SJ: There has been significant investment in the plant in the past few years, which is a great position to be in as the plant manager.
Quite a large part of the investment has been due to compliance with particulate emissions restrictions. We have just invested Euro2.1m on a new baghouse for the cement mills. That project involved taking the roof off the cement mill building, taking out the ESP and installing the baghouse on top. The equipment was from Intensiv Filter and the project was carried out by Fairport Engineering.
In the recent shutdown, we upgraded the vertical raw mill in a Euro1m project. All of the internal components were replaced, including the table and rollers. Prior to that project we were grinding raw meal at 240t/hr. Now we can reach 265t/hr, so we are seeing good payback. The shutdown also saw the replacement of all the coal mill internal components and extensive re-bricking of the kiln.
We have also just invested Euro590,000 on a new Ventomatic packing machine that can fill 4200 bags per hour. It has replaced an earlier Ventomatic that could only pack up to 3500 bags per hour. We also have installed a new palletiser from Ventomatic under the same project. Both of these will increase our capacity for packed products, which our commercial colleagues assure us is a good position to be in going forward. We also commissioned an Arodo Arovac plastic packing system in late 2011.
The plant is also very proud of its 12MW solar farm, which was installed between 2013 and 2015 on 20 hectares of land between the works and the adjoining quarry. It was built by and is now owned and managed by Lark Energy but it is tied into our electrical supply contract. On average it supplies 3MW per day. In the summer we can see figures as high as 6MW and in the winter we might see 1MW. We use around 16MW of electrical energy in total so it is an appreciable proportion of what we need. If for any reason we cannot use the electricity, it goes to the grid. However, this is rare, even during the winter shutdown.
GC: Are there any upcoming projects in the near future?
SJ: In 2017 we will invest Euro10m project to replace the electrostatic precipitator (ESP) on Kiln 8 with a new baghouse. The project will be undertaken by FLSmidth. In the longer term we will be replacing the cooler ESP with a baghouse in 2018 - 2019. This will ‘future proof’ the plant to allow for an increase in capacity from 2750t/day to 3000t/day. We will achieve this by upgrading the ID fan, which, in turn, will be facilitated by a number of other modifications to the plant. Other smaller projects include a Euro710,000 project for road surface improvements and a Euro830,000 project to replace some of the plant’s air compressors.
However, the largest project that we have in the longer term is to manage some pretty extensive changes to our quarry. We have applied to divert the road that runs between Ketton and Normanton slightly northwards and redirect it over a new bridge over a narrow part of the quarry. That will allow us to go south of the road and access further reserves that we already have planning permission for. We are also looking in future to submit a larger planning application to quarry land to the north and north east of the existing quarry areas, which will secure us many more decades of reserves. In some areas we already own the mineral reserves but not the surface, in some areas we own both and some areas we own neither! It will be a big project. A potential longer term solution may be an access road to the north from the plant. This would potentially mean that, instead of our trucks going through the village and narrow roads, they could stay on larger roads and access the main road network more easily.
Fuels and the environment
GC: What types of fuels are used at the plant?
SJ: Our main fuel today is secondary recycled fuel (SRF), comprising waste paper and plastic. We source it from a company called Mid UK through a long term contract. It supplies around 45% of our thermal energy requirements. We also use Cemfuel, which is a branded recycled fuel made from waste solvents. It is supplied by a company called Tradebe UK. It is sourced from a pretty wide area from all manner of chemical processes and comprises about 17% of our fuel consumption. We also use meat and bone meal (MBM) at about 6% of our thermal energy consumption. Combining those three takes us to 68% alternative fuels. The remaining fuel is coal, sourced from the UK. It comes in mostly by rail.
Pulverised coal is provided to the main burner after grinding in a Polysius RM25/12/40 vertical roller mill. Cemfuel is also fed to the main burner, which burns around 45% of all fuels. To the calciner we feed SRF and MBM pneumatically. In 2016 we had to operate without the bypass for three months, following a problem with the main stack. However, everything has been up and running again for a while now and we expect an overall substitution rate of around 65% in 2017.
GC: How has the use of alternative fuels changed over the years since the plant began using them?
SJ: Cemfuel, the fuel made from waste solvents, is actually the fuel that we have used for the longest, since we obtained a permit for it in 1994. The plant used tyres for some years from 1996, but these are no longer used. MBM was introduced in the mid 1990s due to the BSE crisis and the SRF (paper, plastics) has risen steadily from around 25% when we first introduced it in the late 1990s.
We have been able to ramp up the amount of SRF we use by securing a long-term contract with a quality fuel provider. This is where most of the overall increase in alternative fuels has come from. In the past we used to receive baled waste on site and process it but now we receive the fuel directly from the supplier for immediate use in the kiln.
GC: How might the fuels change in the future?
SJ: We are always on the look out for improvements to our fuel mix. Some ideas going forward include burning SRF on the main burner. However, to do that we would need to reduce the size of the particles.
GC: Is the plant at a technical ceiling with respect to the amount of alternative fuels it can handle?
SJ: We are approaching ceilings on two fronts. Firstly we cannot increase the level of SRF, because of introducing too much chloride from the plastic that it contains. On top of that the residence time in the calciner is just 2.2 seconds, well below a modern residence time of 5 seconds or more. This limits the size of the particles that can burn, which somewhat reduces the types of fuels we can use.
GC: What are the public perceptions of the plant’s use of alternative fuels?
SJ: We have a good relationship with our neighbours in the surrounding villages. This is due to our open door policy and regular reporting and meetings. We did not face significant opposition when we first started to use alternative fuels because environmental awareness was not as high then as it is today. At our meetings with local stakeholders today they are pleased to hear that we are burning such large quantities of alternative fuels. We have a strong track record.
GC: What environmental control systems are used?
SJ: Aside from the dust filtration systems that I described earlier, we use lime to control HCl and, to some extent SO2. We put in aqueous ammonia to control NOx as required but, due to the high level of control we have over our fuels and raw materials, we don’t have to use it very often. Dioxins are taken care of by our Lurgi gas tower with Lechler gas conditioning system. I would also like to mention that our bypass dust, instead of going to landfill, is now licenced for use as a fertiliser.
Markets and future
GC: Where are the plant’s markets and how are they served?
SJ: We predominantly ship to the south and south east of England. Around a quarter of our total production last year was delivered to our rail depot at Kings Cross in London by train, from where it was distributed to ready-mixed and precast concrete plants in and around the capital by truck. The rest is sent out by road, from the plant, with around 50% of the total output in bulk tankers and a further 25% in 25kg bags. Typically our road distribution is to East Anglia (Norfolk, Suffolk and Cambridgeshire) and other counties to the north and east of London.
GC: How has the plant (and Hanson) coped with the economic downturn?
GC: While the Ketton plant noted a downturn in demand, we had to mothball Kiln 7 of course, it was not as badly affected as the other Hanson plants at Padeswood and Ribblesdale. That is because we supply a lot to London, where the downturn was not as marked. We have the ability to grind clinker, which can be brought in from our Padeswood plant.
GC: What are your expectations for the future of UK cement demand, especially given Brexit?
SJ: With regards to Brexit, we are just getting on with it. It has not stopped investment for us and the UK population isn’t going anywhere. The UK will continue to need cement. The government has stated that we need to build 250,000 houses a year for the next five years to meet demand, about twice the current position, and is looking at policies to help achieve this, which will be fantastic for the cement and wider construction sector. A recent survey of the main construction companies showed that, since the Brexit vote, they have outperformed the general stockmarket, so things are good for the sector overall.
As well as the need for housing, there is also the HS2 rail project, Hinkley Point nuclear power plant (to which Hanson is the key materials supply), the new cross-London sewer extension, as well as the A14 extension and the A303 tunnel under Stonehenge. There is plenty of infrastructure happening and we have a positive outlook.
GC: What one thing would you change about the plant, regulations, political situation, etc, if you could to best benefit the plant?
SJ: I would build Kiln 9 to secure the long-term future of the site. As the economy improves, we could grow into, let’s say a 4000t/day (1.3Mt/yr) capacity kiln. Then, after we have secured planning permission for the quarry, we could really get motoring. That’s the dream!
GC: Thank you very much for your time.
SJ: You are most welcome.