INDUSTRY FOCUS WATER & WASTE TREATMENT REVOLUTIONARY RECYCLING
After lengthy research, and with the help of control and instrumentation from ABB, a plastic recycler has found a way of recycling all seven groups of plastics
T
he UK presently produces about 3.7 million tonnes of plastic rubbish a
year, and 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. RT’s 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 – 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. The research team had to collect as much data as possible to understand what was happening inside the reactors as temperatures, flow and feedstock were
34 SEPTEMBER 2017 | PROCESS & CONTROL
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 lab experiments. Gary Egerton, ABB UK & IE Business
varied. Then, once they understood what was happening, they had to be able to control it. Given the central role of instrumentation and control, RT decided to outsource the challenge to Charter Tech, an integrator of process control and ESD systems. 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.
Charter Tech used a distributed control system controlled by the Freelance application, rather than using a blank page PLC SCADA approach. Paul Burns, Charter Tech’s business development manager said 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
The pilot plant is running reliably and operating at command, and the next step is to open a commercial plant
Recycling Technologies’ process converts plastic waste into Plaxx
Development Manager, said: “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.” A large product range was certainly one of the benefits ABB offered. This variety of choice meant that, in many cases, they could begin with a catalogue item that was already quite close to what RT wanted. For example, ABB 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. 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 then progressed 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 finalised, 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. Haworth says the pilot plant is running reliably and operating at command. The next step is to open a commercial plant. To make the transition easier, each element has been designed in a modular fashion at a size that can be loaded on a standard truck bed.
ABB
www.abb.com
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