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Selecting a portable industrial combustion analyser

04 February 2020

Jon Bawden, product manager, Testo UK, explains how to select the right combustion analyser for different sizes of combustion plant

Portable combustion analysers with electrochemical sensors can provide the most cost-effective and quickest method of carrying out emissions spot checks or for carrying out commissioning and servicing work on combustion plants. They have the advantage of being very quick to set up and can be carrying out measurements within minutes of arriving on site. 

There are several different types of portable combustion analyser on the market and the choice depends on the type of work to be carried out. Portable analysers, also know as Handheld Emissions Monitoring Systems (HEMS), are suitable for working on combustion plants with thermal input capacity up to 20MW. For emissions measurements on plants over 20MW a Continuous Emissions Monitor (CEMS) or a Transportable-CEMS must be used. In this article we look at features of analysers suitable for working on plants up to 20MW.

Regulatory background

The effects of poor air quality have been well documented in recent years. To improve air quality the UK Government has adopted the Medium Combustion Plant Directive (MCPD) which became UK law in January 2018. New plant delivered from January 2019 must comply with MCPD and there is a phase-in for existing plant depending on the size. It applies to generators and plants with a thermal input of 1MW to 50MW. Plants greater than 50MW are covered by the Industrial Emissions Directive and plants less than 1MW are already covered by the ECOdesign Directive.

Small combustion plants (<1MW)

Combustion Engineers working on Small Combustion Plants less than 1MW should use an analyser which meets EN50379 or optionally an MCERTS-approved HEMS. There are many analysers which meet EN50379. Key factors to consider are whether the analyser has sensors to cover the scope and range of combustion gasses, and also whether it is sufficiently robust to deal with the gas concentrations, temperatures, dust load, flue pressure etc.

Most handheld or portable gas analysers use electrochemical sensors. The sensors have to be zeroed in fresh air before measurements can be made, and should be periodically zeroed during longer term measurements. Simple analysers require the gas sample probe to be removed from the stack in order to be zeroed in fresh air. For greater convenience analysers such as Testo 340 or Testo 350 have fresh air valves which enable the sensors to be zeroed without removing them from the flue or stack. For longer term measurements these analysers can even be programmed to go through measurement and rinse cycles automatically.

In ideal combustion, stack emissions are generally at low concentrations. However, in large systems the CO concentration, for example, can increase rapidly, which is dangerous for the analyser sensors. Analysers with dilution features can automatically mix the gas sample with a predetermined volume of fresh air to dilute the sample, keeping it within the operating range of the sensors.

Industrial processes often involve high dust or particulate loads in the stack emissions. Careful attention is needed in selecting a suitable sample probe for the portable analyser. Probes with built-in filtering options can be important.

To remove excess moisture from emissions gasses some analysers offer gas preparation devices. Testo 350, for example, can be configured with a built-in gas preparation feature which cools the sample gas, removing excess moisture before it gets to the sensors.

Medium Combustion Plant Directive (MCPD)

The MCPD aims to improve air quality by controlling the emissions of sulphur dioxide, nitrogen oxides and dust. It brings a new focus on combustion analysis because it broadens the scope of plant operators required to report on emissions of SO2, NO, NO2 and CO. 

Working on plants from 1MW to 20MW now falls into the Medium Combustion Plant Directive, which means analysers conforming to EN50379 may not be sufficient. HEMs with MCERTS certification will be required. In fact, from January 2025 all analysers used on MCP must be MCERTS certified.

Operating licences for MCP specify Emissions Limit Values (ELVs) which must be periodically measured, with the results recorded and stored for at least 6 years. Often the ELV’s are specified in kg/m3, whereas many portable analysers use ppm as their default unit of measure. Choosing an instrument with selectable units of measure makes life a lot easier, as does combining the analyser with PC software to create professional and paperless reporting.

The Environment Agency established its Monitoring Certification Scheme (MCERTS) over 20 years ago. November 2018 marked the 20th anniversary of the MCERTS scheme. Instrument manufacturers such as Testo have submitted analysers for independent testing under the scheme. In fact Testo is proud to have had products certified for over 10 years. MCERTS certification is a robust process which includes annual audits of manufacturers. 

The scheme gives peace of mind that the analyser provides accurate reliable data which is accepted by the Environment Agency. It also gives the user the confidence that the instrument is robust and fit for purpose. 

Testo 350 has been awarded MCERTS in the Handheld Emissions Monitoring (HEMs) category, which used to be referred to as Portable Emissions Monitoring. The instrument is approved for measurement of O2, CO, NO, NO2 and SO2, making it suitable for many combustion applications, from stack and landfill emissions monitoring, to industrial combustion process analysis.

One of the benefits of portable analysers as opposed to fixed or transportable instruments is the speed of measurement. Even from a cold start, portable analysers will typically be capable of stable measurements within minutes.

A good quality combustion analyser is a must-have in any combustion engineer’s toolkit. They are powerful instruments in saving time through fast diagnosis and efficient reporting. They have to deal with varied and harsh environments which is why product selection is so important.

 
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