The Cemex South Ferriby plant has stood proudly on the Humber Estuary in North Lincolnshire, UK for nearly 80 years. Over the years, the river has been a vital lifeline for the plant to bring in raw materials and export cement. However, in December 2013 the plant was completely overwhelmed by a tidal surge, leaving it with major damage. Here, key plant staff describe the damage, the renovation and the plant’s unusual semi-dry Lepol grate production process.
GC: Can you describe the history of production at South Ferriby?
Jan Peters, Plant Director (JP): The South Ferriby plant began life as a wet process plant, operated by Rugby Group, in 1938. The original line was replaced with two semi-dry Polysius Lepol kilns, the first (kiln 2) coming in 1967 and the second (kiln 3) in 1973. Both have a capacity of 1000t/day, taking capacity to around 0.7Mt/yr. In 2000 the Rugby Group was acquired by RMC, which, in turn, was bought by Cemex in 2005.
GC: What process does the plant use today?
JP: We use clay and chalk from our quarry, which is 1.6km from the plant. It is transferred to the plant site via a long conveyor and is taken to our chalk and clay domes, which have capacities of 12,000t each. It then heads to two double rotator closed circuit raw meal ball mills (both 90/hr), where iron oxide and sand are added.
The raw meal is then processed in a blending silo array, in which each mill has two silos. We can homogenise the raw meal before the kilns by drawing material from each silo as required. From the homogenisation step, the material goes onto the noduliser tables, which is a key part of the Lepol semi-dry process. The fine raw meal is mixed with a minimum of water on four rotating tables, two for each kiln line. The nodules are typically 20 - 30mm in diameter. Obtaining a consistent size is critical for the Lepol process. For those that may not be that familiar with the process, it is essentially a ‘reverse clinker cooler.’ The nodules are pre-heated via a hot gas flow, which starts calcination within the grate itself.
From the Lepol grate, the material heads to the kiln. The excess water is completely driven off and calcination is completed, much as in a dry process line. The clinker coolers are very conventional. From there we have various clinker silos (a total of 45,000t) and two ball mills. We ship cement and clinker in bulk and do not have bagging facilities. We currently produce CEM I, although we are able to produce CEM II as well.
GC: Where do the additives come from – sand, iron, gypsum, etc…?
JP: The area around the plant is rich with minerals. Sand is actually from the next village, while iron oxide comes from Scunthorpe, a large steel-making town. The gypsum is also sourced locally from Fauld mine in Staffordshire. We also use some from recycled gypsum wallboard.
GC: Paper can often be included in the ‘gypsum’ fraction from the wallboard recycling process. Does this cause a problem?
JP: It is not a problem, because the recycled gypsum is currently only 10% of the total gypsum feed. As the gypsum is only added at 5% to the final product, this means that the final cement product contains only 0.5% recycled gypsum by mass. Any minor paper fraction in the recycled gypsum is a very small fraction of the final cement product. However, the question of paper in the gypsum stream may require more attention in the future if we are to increase the use of recycled gypsum.
Flood, damage and renovation
GC: What caused the flood in December 2013 and what was the extent of the damage?
JP: To understand the extent of the damage, we need to properly describe what happened. Low atmospheric pressure, onshore winds and high tides caused a tidal wave to come up the Humber Estuary. The water totally over-topped the banks and road alongside on the south of the Estuary and a 2m high wave came crashing over the plant. It happened at 19:30 in the evening in December, so it was totally dark.
Damian Marsden, Engineering Development Manager (DM): We knew that the weather would be bad, so we were able to minimise the risks to staff. We reduced the number of staff on the night shift. On top of this, we arranged for the workers to park at the quarry, so that their cars were not at risk. We had emergency plans in place, which were followed. This included provisions for high ground areas, which contributed to the fact that nobody was injured.
In terms of damage, the plant was very seriously affected. We lost a lot of structural components and the main office block was damaged beyond repair. At the time the wave came in, kiln 2 was producing cement but kiln 3 was offline and cold. As it was in operation, kiln 2 sustained very serious damage. We had to replace a 22m-long section of the shell because it had bent completely out of shape by the sudden cooling. Kiln 3 was ‘lucky’ in that it sustained ‘only’ peripheral damage. Unfortunately, many of the electrical components were destroyed. We had to replace around 40% of the electrical components.
GC: What was the most challenging aspect of the renovation?
DM: Maintaining health and safety standards was by far the most challenging aspect, especially in the early days. We were dealing with an area that was extremely dangerous: Unstable structures, contaminants, sewage in the water, dead sheep, dead fish. There was no lighting and it was freezing cold. Into that environment, we had to put a peak of 400 staff and contractors. That period was not over quickly. It was two months before you could walk through the plant safely.
GC: What was the most challenging technical aspect of the renovation?
DM: The most challenging technical aspect was the reconfiguration of the control system of the plant. Prior to the flood there had been five local centres for different areas. However, the best solution was to put them together. This is the case now in our temporary control room and it will be transferred across to the new office building, once it is complete.
Just adjusting to the new configuration was itself a challenge. The system was completely new for the operators. We had to test every single item within the control system. That’s 1500 motors and thousands of cables. Every one had to be checked, rechecked and documented. There was also a wider replacement of damaged electrical fittings. Every piece of I/0, every motor, every drive had to be refurbished or checked.
On top of that, many mechanical parts were beyond repair. Major equipment was contaminated with silt, sand and salt. The work was intense and there was a lot of equipment that had to be renovated and replaced, aside from the section of kiln 2 that I mentioned earlier.
GC: Aside from the control room was any other aspect of the plant changed compared to the previous configuration?
JP: Prior to the flood we had several different compressed air stations around the plant. This, like the control room, had grown organically over time. We have now replaced this with a central compressor station, which had lower capital expenditure and is easier to operate.
Aside from those two aspects, the plant is exactly as it was. We replaced everything like-for-like and did not conduct or bring forward any other projects during the renovation.
GC: What has been done or can be done to prevent a future flood or reduce the damage in the event of another flood?
JP: There are two answers to this. Firstly, we are party to ongoing discussions with the local councils and the UK Environment Agency regarding the improvement of flood defences throughout the Humber Estuary. This is a long-term discussion and technical solutions are being investigated.
DM: The second answer is that we now have better procedures on site to deal better with another very large flood. Throughout the rebuild we constantly considered what the quickest solution was in line with modern equipment and standards. Fortunately in some areas the solutions came with inherent flood protection. For example, our motor control centre (MCC) manufacturers could produce bottom entry units quicker and installation contractors claimed time benefits during installation. The result is an MCC above flood level. The new office block will also be planned to be 1.45m off the ground.
GC: Did you ever think, given the damage, that Cemex would decide to close the plant?
DM: There was never any doubt at management level and that was communicated literally overnight to the staff. I was called by the plant manager at 05:00 the day after the flood and he asked, “Are you aware that there has been a flood?” I said ‘Yes’ and, by the time I got to the site at 06:00, the question was, “How do we rebuild this?”
GC: How did Cemex supply its customers in this region when the plant was down?
JP: It was a case of rearranging customers and allocating cement from different facilities, mainly from the Cemex Rugby plant. There was some imported clinker coming from abroad too. The timing could have been worse, because the damage came in winter and demand was fairly low.
Throughout the stoppage, however, every customer was supplied with cement exactly as they would have been normally. There were no complaints. By March 2014 we were supplying customers with cement from the clinker made prior to the flood. It was remarkable to think that so much was damaged but we were still able to use the clinker in the silos!
GC: When did the flames come back on?
DM: It was almost a year to the day of the flood and there was an enormous sense of achievement. We had worked flat out for 12 months and by the time we could restart it was a case of ‘go home and have Christmas.’ It was a big job from the plant staff but we also had a lot of practical and moral support from around Cemex, including colleagues from Mexico. It was a major Cemex-wide effort.
GC: How was the work managed?
DM: The renovation was very difficult, with 300 - 400 persons on site at any one time. Jacobs Engineering was the principal contractor, who pretty much owned the site, taking into account that the entire plant was one construction design and management area. Cemex management and staff were integrated into different teams from Jacobs, with a large number of local firms also sub-contracted.
GC: When will everything be completely finished?
JP: The renovation will be complete when the new plant office opens. This is currently scheduled for the end of 2017, which will be four years after the flood. We are also still completing the lighting inside the plant, which is a work in progress.
DM: Of course the office building is not just an office building: It will house the control room and the laboratory, which, like the office we are sat in, are currently in porta-cabins. The ground has been cleared and we look forward to getting on with the next stage.
GC: Were you aware of any plans to replace the plant with another configuration, for example a dry process line?
DM: Any considerations like that would have been made above plant level and we cannot comment. However, if we had changed the process, the project would have been even more intense than it was. It would also have involved new consultations with local stakeholders, the Environment Agency and a lot of extra investment. The objective was always to supply customers with cement.
Fuels and environment
GC: What fuels are used to fire the kilns here?
JP: We use a mixture of petcoke, a specified solid recovered fuel (SRF) known as Climafuel and secondary liquid fuel (SLF). The petcoke is brought in by barge at Immingham. The RDF comes from Wastecycle and the liquid fuel is a mixture of solvents from Sheffield, around 100km from here.
GC: Can you describe the development of the AF substitution rate at the plant?
JP: The plant started with SLF in 2002 and Climafuel SRF was introduced in 2006. Over the years the use of both fuels has increased. In 2012, the last full calendar year before the flood, the plant was operating with 70% alternative fuels. In 2011 we achieved a world first: the first trial using 100% alternative fuels for an extended period. We are very proud of that.
GC: What effect has the flood damage had on the use of alternative fuels?
JP: Since the flood we have been focused on stabilising the kiln process as far as possible, while we increase the level of alternative fuels. It was easier to reintroduce the SLF, as liquid fuels are relatively easy to burn. Achieving pre-flood SRF levels is proving more difficult, but it would be in any plant like this.
In 2015, with a lot of work, we achieved a substitution rate of 54%, of which around 28% of the total fuel was SLF and 24% was SRF. The target rate for 2016 is more than 60%. We are improving the kiln efficiencies month-on-month and with higher efficiency comes higher potential for using alternative fuels.
DM: I think it is important to highlight just how much of an achievement this has been. You have to remember that the main ‘flood stop’ was not the only stoppage. There have been numerous hiccups along the way, which knocks back the ability to use alternative fuels.
GC: Are there any challenges specific to the Lepol kiln regarding the use of alternative fuels?
JP: The challenges are similar to most other kilns because one of the hardest things is getting the right fuel quality and consistency. One difference compared to a preheater kiln is that we have more capacity in our ID fans. That means that we are not as constrained on the amount of air that can be pulled through the kilns, which allows the extra moisture from the Climafuel to be handled relatively well by the kiln.
GC: Are there plans to introduce other alternative fuels in the future?
JP: Not at present. We are focused on increasing the amount of RDF. We are, however, conducting trials with coal, with a view to replacing petcoke.
GC: What environmental protection systems does the plant use?
DM: We use urea to control NOx and inject lime to remove acidic gases from the stack. For dust we have electrostatic precipitators (EP), both of which are fairly new. This is because, while a bag filter is better at trapping dust, the EPs are more forgiving with respect to the temperature spikes that are typically seen with Lepol grate kilns.
Markets and the future
GC: Where are South Ferriby’s main markets and how is cement transported to each of them?
JP: The plant distributes to Scotland and the north of England. In terms of transport type, everything leaves the plant by truck. Cement for Scotland is loaded onto barges at Grimsby, approximately 40km to the east. Around 25% of the plant’s cement is sent there. In terms of truck distribution to the local area, we supply across the whole of the north of England. Our sister plant at Rugby predominantly covers the south. Both plants also send clinker to our Tilbury grinding plant in the south east of England.
GC: What are your expectations for the UK cement market in the coming months and years, especially given the recent vote to leave the EU?
JP: Like everyone else we are waiting to see what will happen. We know that the fundamentals of the UK construction sector are strong. With respect to the ‘Brexit’ I think a lot of scenarios can be ‘imagined’ but it’s too early to say what will happen.
GC: What one thing would you change about the plant, be it technical, regulatory or otherwise?
DM: Technically, there is only one answer – to replace it with a dry process line. That said, this plant is very efficient within Lepol kiln plants. It has been extensively modified to increase its efficiency. For example, the kiln speed is much faster than it was originally designed for. We push it to the maximum and then go beyond.
GC: Thank you very much for your time.
PJ/DM: You are most welcome.
