Product category:
Solid Waste Disposal and Land Pollution
News Release from: Elga Process Water | Subject: CEDI unit in Bolton
Edited by the Processingtalk Editorial
Team on 18 October 2007
Energy from waste by incineration
A combination of reverse osmosis, CEDI and mixed bed polishing cylinders in two standard 40foot ISO containers provide feedwater for the power generation boiler at the waste incinerator in Bolton
Greater Manchester Waste, a company owned and controlled by the Greater Manchester Waste Disposal Authority, has just completed a multi-million pound improvement programme to its Bolton Thermal Recovery Facility An integral part of the Greater Manchester integrated waste management programme, the facility handles over 125,000 tonnes of Bolton's waste each year which is converted into energy by incineration
This article was originally published on Processingtalk on 17 Dec 2002 at 8.00am (UK)
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The condenser is currently cooled by evaporative cooling towers, although plans are being considered for a district heating scheme that could eventually recover this heat to provide local residents with space heating and hot water, reducing consumption of fossil fuels even further.
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The water required for cooling tower make-up comes from the local River Croal but, to protect the heat exchange surfaces from fouling, the river water has to be filtered to reduce the suspended solids content to less than 10mg/l.
The water treatment system, now six years old, was designed and built by Elga Process Water.
Pumps deliver up to 40m3/h of river water into a 15m3 break tank that provides storage for filter cleaning.
A coagulant chemical is added to the flow to improve filtration and the water is then filtered using two Double Filtration in Series units, each capable of handling 50% of the required flow.
The Double Filtration in Series is a two stage, deep bed sand filter in which the first filter vessel provides a 'roughing' duty and the second stage operates as a 'polisher'.
Separately, the boiler requires about 3m3/h of make-up water with conductivity less than 0.2uS/cm and silica less than 20ug/l, and the deionisation plant that produces it is fed with town mains water.
This is first pre-treated by duty and standby combined organic scavenging and softening units, each containing a layer of cation softening resin and macroporous anion scavenging resin.
This reduces the organics level at the same time as softening the water to prevent fouling of the downstream reverse osmosis unit.
The two resin layers are regenerated at the same time with brine.
The water is de-chlorinated by activated carbon filters and then the pre-treated water is passed through 5 micron filters and then on to a Compact III RC304HF reverse osmosis unit for primary deionisation.
The Compact III uses thin film composite membranes to produce 4m3/h of permeate with conductivity less than 10uS/cm at a recovery of 75%.
The permeate is fed directly into a H060 CEDI unit.
CEDI is short for continuous electro-deionisation, an electrically driven membrane process capable of producing deionised water with conductivity typically less than 0.2uS/cm.
CEDI requires no regeneration chemicals because it is continuously regenerated by an electrolytic process, and the loss to drain is less than 10% of the feed flow.
The treated water from the CEDI unit is pumped to the boiler feed tank via C940 mixed bed polishing cylinders as the final stage of treatment, to ensure that the silica specification of <0.02 mg/l SiO2 is maintained at all times.
Due to the light ionic loading on these cylinders, they are replaced relatively infrequently.
The combination of reverse osmosis, CEDI and mixed bed polishing cylinders produces make-up water of around 0.06uS/cm which, as Greater Manchester Waste's Assistant Operations Manager, Steve Robinson, rather proudly points out, is "good enough for a nuclear power station".
The water treatment plant is built in containers, which minimises site installation time.
Constructing the plant in two standard 40foot ISO containers, one for the Double Filtration in Series system and one for the deionisation plant, meant that they could be completely prefabricated and tested at the Elga Process Water manufacturing site.
On site, the only things that had to be done were the connections to the water supply and drain.
As is the case with most boiler systems, the make-up plant is relatively small in comparison with the boiler capacity and, after a maintenance drain-down, it would take a several days to re-fill the boiler circuit.
"Elga Process Water has helped us there" says Steve.
"They hired us a trailer-mounted, mobile deionisation plant which filled the system ten times quicker than our make-up plant would.
It was all done very professionally: it was here on time and connected up and operating within a couple of hours".
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