Cement plants are increasingly required to install continuous emission monitoring systems (CEMS). While these represent a significant financial outlay, a range of other factors also need to be considered when selecting a suitable CEMS.
To the inexperienced, selecting a suitable CEM can mistakenly be considered as simply ensuring that the applicable national regulations (eg MACT in the USA, Industrial Emissions Directive in Europe) are adhered to, with the necessary international quality assurances for the product to validate the instrument choice.
Whilst it can be quite straightforward to select an instrument that meets the MACT and associated Performance Standards (PS) in the USA and EN 14181’s requirements in Europe, for example, is this really all that should be considered when making such investments?
With continued financial uncertainty in many parts of the world, the purchase cost of such equipment is not an insignificant factor, but really should not be the sole factor when making such decisions.
Selecting the most suitable CEM should take into account how the instrument can benefit the plant itself with added-value benefits such as enhanced process control, which can in turn aid plant optimisation and therefore provide financial benefit to the customer. Alongside this there are the ongoing costs associated with the operation and maintenance of the equipment, with factors such as the cost of instrument air for purging, if required, or the level and frequency of service and maintenance for the product.
A holistic assessment approach
The most valued assessment of a CEM purchase should incorporate a holistic overview of all costs that can be incurred and also those that can be saved from use of the product. It is easy to be blinkered to the differences between initial purchase costs, but really it is the lifespan costs and benefits that need to be considered.
Both Environnement S.A and their particulate monitoring subsidiary, PCME Ltd, also understand that CEMs, especially in developing economies, are often seen as a grudge purchase that is a drain on profitability. To overcome this view, both Environnement S.A and PCME Ltd have developed a range of Gas and Particulate monitors which not only reduce the cost of ownership in comparison to more traditional instruments but also to offer a direct cost saving benefit for the Cement manufacturing process.
In this paper we will discuss both Environnement S.A and PCME Ltd’s unique approach to CEMs monitoring and the additional benefits that their instruments can provide beyond simply monitoring Gas and Particulate.
What should be considered when selecting a Particulate Monitor for Cement Processes? The first priority is to properly define what is required of the instrument in terms of measurement or in addition for Baghouses leak or broken bag detection, and then to clarify if there are any limitations to technology choice by regional regulation or operating permit.
In many countries, the selection of instrument technology is left to the end user making the choice of both instrument manufacturer and instrument technology quite extensive and often somewhat of a challenge. This being the case it is often wise to look at exactly what the instrument can bring in terms of additional features and benefits before a purchase is made.
The performance of a particulate instrument for instance is greatly influenced by the type of dust abatement plant that is being used. In Cement plants, for example, this is normally either Electrostatic Precipitators (ESP’s) or Baghouses which are becoming more commonly used as the worldwide driver for lower levels of particulate emission from industrial processes gathers pace in countries like India (17 Industries legislation).
Dust measurement technologies can be grouped into two types. Firstly, optical technologies, which encompass both
traditional opacity and laser light scatter instruments, are normally favoured for ESP applications. The second group of dust monitoring instruments can be defined as probe electrification devices. This grouping includes traditional triboelectric (DC), AC charge transfer technologies and European QAL1 certified ElectroDynamicTM measurement instruments. Probe electrification devices should not be used on ESP applications as their particle charge transfer monitoring technology can be affected by the operation of the ESP, which will change the particle charge characteristics. This leads to errors in the measurement signal generated in the instrument. Therefore, these dust monitoring devices are best suited to bag filters. Moreover, the limits of each technology in terms of dust loading levels, process temperatures, stack diameters, etc also need to be taken into account.
Once the most suitable instrument has been chosen, the availability and ease of maintenance of the equipment should be evaluated.
Laser Scatter systems are rapidly replacing Opacity instruments due to their ease of installation (single point), their proven measurement capabilities < 1mgm3/>300 mg/m3 (QAL1 approved and US EPA PS11 capable) and Opacity instrumentation’s limited resolution which now makes it often inappropriate for use in the new lower environmental limits being demanded by regulation worldwide.
In choosing the correct laser device, care should be taken to select an instrument without critical moving parts especially when the monitoring section is installed directly in the often harsh environment of combustion chimney stacks. Also, consideration should be made to the materials of construction, for instance in higher temperature applications fibre optics can become opaque leading to instrument misreadings and shorter maintenance intervals which by the very technical nature of Scatter systems is often untaken by skilled instrument engineers.
Scatter systems can be used on both ESP and Baghouse applications but consideration should be made regarding the availability of skilled instrument technicians to due routine maintenance and the requirement of this type of instrument for 24 hours a day air purging with good quality, clean and dry air.
An Alternative for Baghouses
As an alternative to Optical devices, many Cement manufactures, in both developing economies and in countries where the monitoring of particulate has been the norm for many years, are utilising Probe Electrification devices for both Compliance and Process monitoring.
Probe electrification technologies
Many cement producers that regulate dust emissions with baghouses use probe electrification devices for both compliance and process monitoring.
Early versions of probe electrification devices (triboelectric and AC charge transfer) share common issues such as probe contamination in triboelectric instruments, and sensor insulation fouling in both tribo and AC charge transfer instruments. This leads to incorrect (often low) readings and a general feeling that these types of instrument could not be guaranteed to perform well without relatively high levels of maintenance, especially when used as measurement devices. ElectroDynamicTM instruments that utilise a non-contact charge induction technique monitored at a specific band width have overcome the contamination issues traditionally associated with probe electrification devices.
The ElectroDynamicTM Sensor The ElectroDynamicTM sensor is unaffected by particle build-up on the sensor rod. This eliminates the cost of air purging encountered in optical devices.
Unlike traditional Triboelectric and AC charge instruments, ElectroDynamicTM sensors provide automatic sensor health checks to monitor fouling of the sensor insulator to warn if the insulation material is being breached (an issue normally found in high dust loads, eg 100mg/m3 or in applications which damp dust is found, eg some Cement mills). The technological benefits found in ElectroDynamicTM devices and the sensor test features including automatic drift checks which they incorporate result in the reduction of in maintenance time required to keep sensors working correctly and ensure the integrity of the measurement.
Cost-saving maintenance tool
A further benefit when using ElectroDynamicTM systems with baghouses is the opportunity to use the instrument as a cost saving maintenance tool in addition to its role as a compliance instrument.
Used with either individual or multicompartment baghouses, baghouse bag row faults can be identified before high dust levels are found at the emission stack. This allows proactive maintenance programmes to be undertaken, saving costs in labour time, filter downtime and re-bagging costs. It not only saves in operational costs of the filter, but also reduces total particulate emission releases to the atmosphere by improving filter performance.
Range of emissions to be measured
The rising use of waste-based fuels in the cement industry, both for economic and Environmental objectives, combined with the strengthening of air emission regulations around the world is pushing many operators to face a wider list of pollutants to monitor this, with associated costs. The design of appropriate solutions meeting local regulation is the key to maximize the cost benefit of the fuel while maintaining good relationships with local authorities and populations.
Aside from the usually requested parameters, like SO2, NOx, CO, total particulate matter, and NH3, additional parameters can also be measured such as HCl, HF, Dioxins & Furans (PCDD/PCDF), Mercury (Hg) and VOC/TOC.
The monitoring of each gas pollutant, when required, can present specific difficulties, but in general keeping the cost low means trying to operate a multi components analyzer able to measure all of them, except Dioxins & Furans and Mercury which requires very specific technologies and dedicated sampling devices.
Environnement S.A (France) has developed a broad range of analyzers and sampling systems dedicated to meet cement operator needs according to their local regulation. Some of these solutions are described below:
The MIR 9000H is a new generation of heated NDIR analyzer able to simultaneously measure traditional components such as NOx, SO2, CO, CO2 and O2, as well as H2O and pollutants like NH3 and HCl, representing a very cost effective, turnkey solution. This analyzer was designed to be operated without any chiller or catalytic oven, allowing the flues gas directly into the measurement cell without any kind of disturbance. As the entire system is heated to 180˚C (~360˚F), no condensation can occur, even in conditions with up to 40 per cent moisture. This analyser’s robust design is particularly suited to demanding wet stack gas mixtures, including those with potentially-high NH3, HCl and HF content. This analyser is completely immune to NH3, HCl and HF: both its integrity and its metrological performances are unaffected by these chemicals. As a cost-effective heated analyser, the MIR 9000H is also an ideal solution for process control to monitor ammonia slips in SCR/SNCR processes, where either ammonia or urea can be used. It is important to emphasise that in the case of urea, MIR 9000H takes into account the N2O which is created as a byproduct. MIR 9000H can also cope with formaldehyde, a compound which can be produced with some types of fuels and cause issues to NDIR measurements.
For low SO2, HCl or NOx concentrations, the SEC-MIR9000 system combining an exclusive membrane-based drying technology (sampling) and state-of-theart NDIR multigas analyser provides an effective solution. It allows for the measurement of a wide range of pollutants, including CO, CO2, HF and TOC, as well as N2O and formaldehyde for interference correction purposes. The SEC-MIR9000 system, while being an extractive system, also exists as an in-situ all-in-one setup (MIR IS). Very low NOx concentrations can also be measured with a chemiluminescence CEMS bench, either as an option of an NDIR system, or as a standalone analyser.
In addition, Environnement S.A was one of the first companies to introduce Fourier transform infrared (FTIR) technology for CEMS applications. This technology allows the monitoring of a wide range of pollutants, including SO2, NOx, CO, CO2, NH3, HCl, HF and VOC/TOC, with low measurement ranges, making it the ideal solution for the strictest regulations.
Recently, Environnement S.A have also added the TDLS technology (Tunable Laser Diode Spectroscopy) to their portfolio and offer either in situ cross duct or extractive solutions allowing selective measurement and a fast response time of parameters such as NH3, HCl, HF, NO, CO, O2 and H2O with the LAS 300 XD analyser.
However, measuring just the concentrations of the ‘common’ pollutants does not qualify the full environmental impact of an emission release point. The mass reporting given by the stack flow measurement when linked to gas and dust CEMS, as well as the dioxin and mercury emissions, are also highly important. Environnement S.A has launched on the market in the past years, different solutions for flow measurements, QAl 1 certified and considered as Best Available Techniques.
The burning of waste and other alternative fuels increasingly causes concern about dioxins and furans in the community surrounding the cement plant. The AMESA-D continuous sampler allows for the ongoing measurement of dioxin emissions and is already considered the standard for monitoring dioxins/furans (PCDD/PCDF) around the world.
There are other emissions of compounds which are more difficult to monitor continuously. While mercury (Hg) can be monitored continuously, for plants with low concentrations in the range of μg/m3 the accuracies of the existing mercury CEMS depend very strongly on the experience and maintenance efforts of the operators. In addition, the availability of such systems remains restricted. The continuous Hg sorbent trap measurement system (STMS) AMESA-M represents a cost-effective alternative to mercury analysers, especially when the limit or detection is low, and complex and expensive technologies are necessary. Based on the adsorption trap method described in the performance specifications 12B of the MACT standard for the continuous monitoring of mercury emissions, the system is suitable for nearly every application.
The AMESA-M system requires very low maintenance and is adapted to the different flue gas conditions and requirements given by the operators. Its availability under difficult flue gas conditions is almost 100 per cent.
In recent years, Environnement SA has launched different solutions on the market for flow measurements, QAl 1 certified and considered as Best Available Techniques. To ensure accurate, reliable and stable measurements, the Stackflow® series has been designed to measure the flow using a flow profile technique.
The Stackflow 400 is an advanced flue gas flow measurement system for continuously monitoring releases from industrial sources complying with international monitoring standards. Based on ultrasonic technology, it offers an extended measurement path (400mm) for accurate and increased representative measurement. It satisfies the need for high quality assurance on emission release data, reporting mass emissions (kg/year) as well as concentration monitoring. An angled probe version is also available to fit existing perpendicular ports (patented) and consequently, reduce costs.
The Stackflow 200 uses the wellestablished averaging Pitot technology to provide continuous emission monitoring of flow, temperature and pressure for the direct calculation of the corrected value of flow upon the standard conditions. Both are installed on single point installation and make on-site work easier for set-up and maintenance.
Toward full compliance Environnement SA operates a continued development programme to maintain its position at the forefront of advanced environmental monitoring solutions. Its extensive knowledge and experience enable the company to help cement plants ensure full compliance with local, national and international environmental directives for environmental monitoring, measuring and reporting, together with optimising plant efficiency.
By Environnement S.A and PCME Ltd, UK. All rights reserved