ABB Control and Instrumentation solution used in revolutionary plastic recycler
12 June 2017
The UK presently produces about 3.7 million tonnes of plastic rubbish a year, and the job of dealing with it is probably the waste management industry’s least favourite.
Unlike metals, which are lucrative, or glass, which is easy, the rewards of dealing with plastics are few and the difficulties many. Of the seven groups that plastics are divided into, only two are recycled at all: polyethylene terephthalate, used for drinks, and high-density polythene, which is what shampoos and cleaning products generally come in. But according to the 2016 Plastic Market Situation Report produced by the Waste & Resources Action Program (WRAP), bottles make up only 800,000 tonnes of the 3.7 million total. What’s more, they are not truly recyclable. Rather, they are “downcycled” into a lower grade product, such as garden furniture. The result is that 3.3 million tonnes of plastic waste is either burned or goes to landfill, and the only justification for that is that there is no alternative.
Soon, however, that excuse may no longer be acceptable, because a Swindon-based start-up called Recycling Technologies (RT) is currently developing a process that is able to turn all seven types of plastic waste back into raw material. The question now is whether it can turn that process into a full-scale commercial operation, and if it can, how it has managed to solve a problem that has beaten all the other chemists who attempted it.
What the process does
RT’s process is based on a work experiment performed in 2010 Warwick University. The experiment demonstrated a way to use heat to crack the polymers that make up all plastics and turn them back into their original monomers. RT’s project developed this concept as the basis of a chemical engineering process, and fits that process inside a business model that creates the possibility of transformational change on a global scale.
The process works by pyrolysis: that is, it extrudes the waste plastic into a circulating fluidised-bed reactor heated to around 500°C in the absence of oxygen. This breaks it down into particulates and gases that can be separated into hydrocarbons and non-hydrocarbons. The former are condensed into an end product called Plaxx – for all intents and purposes a kind of sweet crude oil – or used in a second fluidized bed at higher temperatures, thereby providing the heat required to make the process work. This is the world’s first commercially viable technology which is able to recycle a waste stream made up of unsorted plastics.
This may sound simple enough in theory, but it has proved challenging to set up outside the laboratory. Adrian Haworth, an energy industry veteran, is the company’s marketing manager. He says much of the past four years has been spent working out how standard grades of Plaxx could be obtained from a variable feedstock – Easter egg wrappers in April, turkey wrapper in December, as he puts it. As this was novel research, the team had to collect as much data as possible to understand what was happening inside the reactors as temperatures, flow and feedstock were varied. Then, once they understood what was happening, they had to be able to control it. Haworth says: “It’s complex. There are several feedback loops, not just one, and the integration of the loops is itself complicated. We needed sensors that could measure the different environments, and we needed very reliable control systems.”
Control and instrumentation
Given the central role of instrumentation and control, RT believed it would have to design its own. After some discussion with a company called Charter Tech, a specialist integrator of process control and ESD systems, back in 2013, it decided instead to outsource that part of the challenge. Paul Burns, Charter Tech’s business development manager, says: “We got to know RT about four years ago through the work we’d done at Imperial College’s chemical engineering facility. They said they were looking at a proprietary system for instrumentation and controls, and I said that’s all well and good but how are you going to support it in the future? I said, if you go with a big supplier, you can focus on your process and the innovation rather than worrying about the control system.” The combination of Charter Tech and the ABB platform offered the flexible approach required by such an untested technology.
What RT was envisaging was a global network of RT7000 recycling units, each feeding back information to its central hub. The control system had, therefore, to allow RT to monitor what was happening with remote units and offer advice as needed. The process is hazardous, so it also required a safety integrity level 3 logic solver, and although the plant was compact, its internal three-tank structure was complex, so a distributed IO control system was needed.
Charter Tech, an ABB channel partner, put forward ABB and a rival for consideration. After careful review RT decided to source its control, instrumentation and drives from ABB, and employed Charter Tech to provide the control solution. In effect a turnkey contract for the vital instrumentation and control elements of the package. Both these companies then became RT’s development partners. For Charter Tech, that meant showing RT’s technicians how it had set up the control and safety system, and thereafter being available as and when required. For ABB, there was a longer lasting involvement as its catalogue had to be searched and adapted to meet the particular challenges posed by 1,000°C fluidized reactors.
Charter Tech used a distributed control system controlled by the Freelance application, rather than using a blank page PLC SCADA approach. Burns comments that the control system is fairly standard, and Freelance, being an entry level DCS is very flexible and the ideal package for a pilot plant. Flexibility, ease of use, together with a remote IO node offered a scalable solution that could be easily transferred to the production model. It allowed IO to change location from one node to another without large scale reworking of the system. Where Charter Tech really made a difference was in making rapid adaptations to the system as RT found out more interesting things about depolymerisation that had not been apparent in Warwick’s lab experiments.
“Because it was a pilot plant, they were constantly changing things and that was the biggest challenge for us. However because we are a small organization we have the ability to react quickly. The process was dictating things, and our competence with the product meant that we could implement the changes quickly. We were able to react, implement and conclude.”
Gary Egerton, ABB UK & IE Business Development Manager, says the instrumentation was a stiffer challenge. “The process contains many high temperature and abrasive environments within it which had to be considered in relation to specification of instrument in order to maintain their high accuracy and integrity over long periods of the plants operation. Our product management team worked closely with the project engineering team from the beginning to ensure that we provided the very best solution on each part of the process to achieve this requirement. A great example of this, was the use of ceramic thermowells which were engineered to provide accurate temperature measurement in the most extreme conditions of the plant, as per the customer requirements.”
In this respect, Burns’ advice paid off, because ABB had such a variety of choices that in many case they could begin with a catalogue item that was already quite close to what RT wanted, for example it was able to supply high accuracy electromagnetic flow meters for conductive liquids, high accuracy Coriolis mass flow meters for mass flow measurement, as well as variable area flow meters. “It wasn’t a case of someone sending a specification sheet and our quoting engineers looking at it – we brought our top product managers expertise to sit alongside RT in the consultative phase of the project and that's not something that all companies would have the capabilities to do,” says Egerton.
Hawarth says: “We’ve had a lot of advice from ABB on which sensors are the right ones for the application we have because of our strange environments. We go to them and tell them ‘look we’re trying to measure this flow and we’re having difficulties – what do we do?’ So they come back and tell us to try a radar type or a microwave that we hadn’t thought of.”
Naturally, there is a price to pay for this extra service – all the more so since RT was pretty much living hand-to-mouth on crowdfunding and risk capital from a few angel investors. Haworth says: “There is often a tendency when you’re an SME running off your own capital to go with people who offer you prices that are lower than the market price. We learned from experience that that’s not always the best way to go. Both Charter Tech and ABB are providing great support and so we’ve made the decision that they are our strategic partners.”
Once it had its instrument and control system in place, RT operated a small-scale facility in Swindon that handled about 1 kg of feedstock per hour. It was during this period that it built up a picture of how variables affected the chemical processes. After it worked out how to control the output from this bench-scale unit, it moved up to a pilot plant that was able to deal with 100 kg of plastic an hour. This began work last June and proved that it really could make Plaxx from all seven grades of plastic. At the time of writing, the company has set up its pilot plant at a site provided by Swindon council, who will also provide a flow of plastic to process.
During this period the control system was finalized, so that temperature and flow could be adjusted in response to changes in the kind of feedstock, with the overall aim of producing the desired grade of Plaxx. Quite early on, RT was happy that the control and instrumentation system were up to the job. As Haworth says: “The thing we’ve had the least problem with has been the instruments and controls. Most of the issues have been basic mechanical problems or flow problems. Getting things sized right, getting the right temperature, getting the sand movement the way we want it, getting the fluidization right or getting the plastic fed into the machine in a homogeneous way.”
Now RT believes that it is almost there. According to Haworth, the pilot plant is running reliably, operating at command, and there is a queue of people coming from “Africa, Japan the US, South America, Saudi Arabia” to take a look at what it does.
The next step is to open a commercial plant, which is earmarked for a site near Perth in eastern Scotland. Once the process is proven, it can emerge from the “valley of death” and begin to solicit serious money from many potential sources, foremost among them, one presumes, a plastics industry eager to shed its image as a polluter of land and seas. To make the process easier to mass produce and set up at waste treatment facilities, each element has been designed in a modular fashion at a size that can be loaded on a standard truck bed.
So, to answer one final question, why has nobody else ever done this? Haworth says it is not because of the complexity of the chemical formulae. “Anyone can do what we do with a home chemistry set. What is hard is putting that into a robust industrial system. Other people have tried and for various reasons they haven’t been successful, but with our model we're sure as soon as we demonstrate our robust system, people will be lining up to get involved and take one of our machines.”
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