Waste treatment with a renewable motive
Sludge handling technologies have changed greatly in the past few years. CSG is one product supplier that has had to adapt to meet new demands for sustainable solutions.
With an ever increasing demand for energy, and international government pressure on industry to both clean up its act and make energy savings, Castings Services Group (CSG), a leading supplier of quality civil engineering products serving the sewage and wastewater industries, is just one organisation that has had to adapt and develop its product range to meet customer demands for sustainability focused solutions, and to recoup energy gains from sludge.
Wastewater treatment plants are big consumers of electric power, especially when nitrification is involved in the biological process. Therefore it is highly desirable for plants to recover and optimise energy that is contained in the sludge they generate. Energy recovered from the sewage sludge goes a long way towards making the wastewater treatment process energy self-sufficient, and in some cases producing a high percentage of the requirements of the entire treatment works site. This eliminates the need for large amounts of grid electricity and therefore has the dual benefit of cutting energy use and costs.
As a leading supplier to the water and wastewater industries, CSG’s product portfolio has been specifically designed to ensure their customers are ahead of the game in sludge handling technologies, such as Anaerobic Digestion (AD), and Advanced Anaerobic Digestion (AAD) which allow the recovery of energy in sludge generated by a wastewater treatment plant, to be converted into electric power.
"As the industrial landscape has evolved in the production of energy from waste,
Dave Warner, divisional manager of CSG’s Process and Actuation Division, said: "For decades we have been providing solutions for the sewage and sludge industries. However in recent years, as the industrial landscape has evolved in the production of energy from waste, we find ourselves facing a different set of circumstance to overcome on behalf of our customers mainly in the control of imported sludge.
"We are presented with challenges in the types of products and solutions we offer to our customers. Whereas, a decade ago we were dealing with sewage, now as energy from waste sites and landfill we deal with the by-products of releasing energy from sludge, including leachate and various imported waste like oils and fats. These occur in varying concentrations, can be of an irregular consistency and are incredibly pungent and attack elastomers on the sludge handling equipment."
Warner continued: "The treatment methods of some of the sludge produced vary widely, for instance to kill e-coli the sludge needs to be heated to over 72°C and held at this temperature for over an hour. This gives us an issue in terms of providing a valve system with an elastomer resilient to these sustained high temperatures.
"A gate valve with an EPDM wedge is no good as oils and fats will expand the rubber; nitrile has a heat limitation, so we consider products that contain Viton (FKM) of neoprene which is a bit non standard for the UK market. Additionally, we still encounter the usual ragging up and now we are also finding on the energy from waste sites that you can find the odd solid object such as glass, wood, bottle tops which again can damage a seal."
One of the most significant renewable technologies in addressing Britain’s international commitments to address climate change is that of AD, and in the last five years AAD which recovers significant quantities of energy from sludge. AD is the breakdown of organic materials by natural bacteria to produce biogas from waste biodegradable materials including sewage sludge. AAD takes this process one stage further, and significantly enhances the benefits of anaerobic digestion by separating and optimising the key process stages used in more conventional digestion systems.
CSG’s new Process and Actuation Division recently completed a project working with GTM, the Galliford Try and Imtech Process joint venture, on Anglian Water special projects, which involved specifying and supplying the complete scope of valves for two Anglian Water projects with a combined value of £320,000.
The two installations were designed to enhance the AAD facilities at both Basildon and Cliff Quay Sewage Works in Essex by capitalising upon the generation of gas for renewable energy such as electricity, consequently boosting sustainability.
CSG supplied valves equipped to handle efficiently each stage of the AAD process including:
• Robust Orbinox bi-directional knife valves designed to cope with the raw dense waste
• Mueller eccentric plug valves which manage the flow through the pipes
• Butterfly valves that will effectively adjust levels of gas
The Mueller eccentric plug valve is an ideal product to use on screened sludge for isolation and control applications. The plug valve can be installed having the seat on either the inlet or outlet side of the valve. This bi-directional function means that when the valve is closed the media doesn’t become trapped within the valve body, thus keeping the bearings out of the sludge, offering greater protection and giving a longer life expectancy.
The natural closing action of a plug valve means that you get an increased velocity across the seat removing any debris that might prevent closure.
For unscreened sludge, the bi-directional Knife valve made by Orbinox is the true market leader, the EBES valve is ideally suited for this type of application offering a full bore with no areas for snagging. The elastomer that gives a tight shut-off is an edge seal encapsulated within the valve body again outside the flow.
The main advantage of an Orbinox Knife valve over a wedge gate valve is that the spindle and wedge nut are all outside the flow, meaning the valve will not rag up an cause the valve to fail which is a common complaint on a wedge gate valve.
For screened sludge CSG recommend fitting either metal-seated wedge gate valves that are ideal for isolation, and have been used successfully for many years in the control of screened sludge. Or, alternatively swing check valves are often specified, which are installed complete with the lever arm counterbalance weight and protective guard.
Warner said: "At CSG we wholly support new technologies designed to promote renewable energies, AAD offers not only a waste treatment solution but one that delivers a significant energy source and a reduction in sludge volumes. We believe supplying our products to renewable energy projects such as Anglia’s will be a big growth area for our business moving forward."
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