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Study looks at role of sensors in energy from waste plant

A company behind the development of emissions testing and pollution control in energy from waste (EfW) plants has published a case study on its technologies.

 Viridor's energy from waste plant in Runcorn

Viridor’s energy from waste plant in Runcorn

Released by pollution monitoring and gas analysing technology company SICK UK of St Albans, the case study explores the new INEOS Viridor EfW plant at Runcorn and its use of emissions monitoring technology.

The study written by the company is published in full below. It highlights the importance of sensors to maintaining uninterrupted operating efficiency, as well as setting in place the right arrangements for maintenance and servicing.

Emissions technology in Cheshire

The Runcorn Energy from Waste (EfW) combined heat and power facility is designed to receive about 850,000 tonnes of refuse derived fuel produced from non-recyclable wastes arising from local authority (eg. Greater Manchester) and local business contracts.

The facility is capable of generating up to 70MW of electricity and up to 51 MW of heat for exclusive use by INOVYN at its neighbouring Runcorn site with chemical manufacturing operations, helping to secure a major source of employment within Halton.

Continuous monitoring to meet stringent environmental regulations, especially the Waste Industry Directive WID/2000/876/EU, is essential to the plant’s operation. At the same time, high levels of operating efficiency are demanded without interruption.

Consistently accurate and reliable 24/7 gas measurement and monitoring systems therefore make a vital contribution both to pollution-free operation of the plant and for optimal control of the combustion processes.  Regular planned servicing and Quality Assurance monitoring of the instrumentation are also critical to achieving ongoing regulatory compliance.

Rhodri Jones, SICK UK project & environmental specialist – process automation, explains:  “The Runcorn plant was built as a turnkey design and build contract by Keppel Seghers, who specified an integrated package of gas monitoring and analysis from SICK, based on their previous experience working with our instrumentation on other projects worldwide.

“SICK UK has the ability to provide the essential instrumentation capability to meet the requirements of the Industrial Emissions Directive (IED) for continuous, recorded and fully-traceable quality standards.

“SICK sensors are installed, firstly, for measurement of untreated raw gas to provide essential data for optimum combustion performance in the incineration process. Secondly, emissions monitoring of stack gases is also provided by SICK to help ensure the plant meets air pollution regulations, and complies with the site’s Environmental Permit.â€?

RDF delivery

Around 20,000 tonnes of waste will be converted into RDF and sent to Viridor's Runcorn EfW

Viridor’s Runcorn EfW plant is capable of treating up to 850,000 tonnes of non-recyclable wastes from businesses and local authorities

Pre-treated Refuse Derived Fuel (RDF) arrives by road or rail and is unloaded at the main reception hall, then held in the main fuel bunker. RDF is fed to one of four incineration lines where it is heated to 850 deg C using heat from the previous RDF combustion, under strictly controlled and monitored conditions.

As part of the proprietary Keppel Seghers solution, a variety of technologies is used in the flue gas scrubber to treat waste gases from the combustion chambers. For example, hydrated lime is introduced into the raw flue gas stream to reduce the emission of sulphur dioxide and hydrogen chloride. Activated carbon is also injected to adsorb total organic carbons, heavy metals and polychlorinated biphenyls.

Dust from the combusted waste is captured in a bag filtration system over a large surface area.

SICK instruments are installed to analyse the raw gases before and after purification in the scrubber.  They provide real-time feedback for control and optimisation of the combustion and purification processes, and meet obligations under WID and the site Environmental Permit.

Before-and-after sensing

SICK MCS300P analysers are installed for raw gas measurement to measure levels of sulphur dioxide and hydrogen chloride on the inlet, as well as on the outlet of each scrubber. These signals are used to automatically determine the levels of lime to be injected in the scrubber.   One of the benefits of this installation is ensuring the gas stream is not over-dosed with neutralising agents which leads to more cost-effective plant operation.

The analyser uses a well-proven hot/wet extractive system, based on non-dispersive infrared and gas filter correlation principles to provide a continuous measurement. The SICK MCS300P’s automatic purge system prevents clogging of the sample filter by untreated gases.  The analysers can be calibrated directly or via a sample probe making them easy and quick to use for the operators and sensor engineering team.

A SICK Dusthunter SB100 measures dust content in the gases on each inlet. The Dusthunter determines in-situ dust concentrations in mg/m3 using back-scattered light from an emitted laser beam. A great benefit of the technology is that its sender and receiver are contained in one unit. The instrument can therefore be inserted or accessed from only one side of the gas duct, reducing installation and maintenance/inspection costs.

The main exhaust stack consists of four flue ducts, each carrying waste gases from the four combustion chambers.  Further SICK gas and Dustbuster monitoring instruments are positioned in the flue ducts at critical monitoring points. Two SICK Flowsic 100 Gas Flowmeters also provide final monitoring of the emissions prior to exhaust to the atmosphere.

The SICK monitoring system measures emissions on a continuous basis in the stack and half-hourly and daily reports are automatically collated for Environment Agency verification to comply with the facility’s Environmental Permit.

Measurements and monitoring from all the SICK instruments are collated by SICK MCS 100FT monitoring and analysis systems housed in cabins at the base of the main stack, from where the data is uploaded via SICK’s innovative Meeting Point Router (MPR) to the Runcorn EfW plant Distributed Control System (DCS) network.

Back-up

In each cabin there are three SICK MCS 100FT analysers, two for each combustion  line and a third redundant analyser as an automated back-up that can provide immediate sampling and reporting, should a fault occur with the operating systems. This ensures waste can continue to be burned without interruption and avoids a shutdown in the event of a failure to monitor pollution.

The complete system facilitates effective and real-time combustion control to ensure the most efficient combustion of the waste, both for energy yield and to minimise pollutants.

To provide complete robustness and reliability of the system, the instrumentation package is integrated by the MPR to facilitate remote diagnostics and calibration, as well as communication with the Viridor DCS network.

QA monitoring

The fulfilment of EN14181 Quality Assurance of Automated Measurement Systems (AMS) is a critical part of meeting the facility’s Environmental Permits and WID compliance as well as giving Viridor total confidence in the measurement data generated.

SICK’s service engineers attend the site every week to carry out QAL3 calibration checks on all six MCS100FT analysers using certified gases as a comparison. In addition, six month preventive maintenance visits and annual functional and linearity tests provide further layers of assurance. Routine assessment of the measurement and analyser condition status is an essential part of SICK’s contribution to the continuous operation of the EfW site.

[Note: article amended October 2016]

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