Air Monitoring 33


In gas measuring applications, PEMS can be used either alone or alongside CEMS to improve effi ciency and accuracy.


coupled its comprehensive CEMS offering with its digital expertise to provide a wide range of solutions for all environmental applications. This helps operators to comply with regulations, reduce costs and maintenance, optimise emission monitoring, and improve system uptime.


Benefi ts of PEMS


A key benefi t of a PEMS system is cost. Compared to an equivalent CEMS, PEMS can typically reduce lifecycle costs by up to 50 percent over a space of fi ve years. This is because the lack of any measurement-related hardware means that the purchase cost is much lower, and with no physical equipment required apart from a PC from which to operate the software, there is no need for continual equipment maintenance beyond adjusting the software model and calibrating. A PEMS also does not need replacing as any changes can be managed through updates to the software, server or operating system.


Another benefi t is speed of implementation. PEMS can be installed more quickly, with less training required to be able to use the system. As long as the system has an online connection, it can be operated remotely either by in-house staff or a third party.


While a CEMS can fl ag up excess emission levels, it typically does not provide any insight as to why they have occurred. In contrast, a PEMS can use dynamic set points to trigger alarms based on information inferred from historical events. The more data the system parses over time, the more accurate it can become.


ABB’s PEMS applications take this a step further by utilizing Inferential Modeling Platform. This is the product of decades of experience in emission monitoring and modeling applications to provide an easy-to-use, powerful and effi cient tool to develop and deploy advanced mathematical models and to deliver the specifi c functionalities prescribed by the environmental regulations (e.g. US EPA Performance Specifi cation 16, EU TS-171198). Its Sensor


Validation system pre-analyzes the input values before feeding to PEMS models, preventing the PEMS from inputting faulty variables that could affect the quality and reliability of the system’s operation. This makes it possible to verify in real-time that PEMS inputs are consistent and, where applicable, replace faulty values with reconciled ones to maintain high accuracy. This advanced sensor validation system allows to keep PEMS output quality assured and further increasing the availability of the system.


A PEMS example


ABB’s PEMS solutions have been implemented at various sites around the world. In one application involving a major oil and gas company, the solution is being used to help measure gas turbine emissions. In this application, a temporary CEMS analyzer was used to acquire proper emissions data to help develop and design the appropriate models for PEMS, with process data simultaneously being collected directly from the plant distributed control system (DCS). The data collected was designed to cover the widest range of process conditions.


Data processing, model design and offl ine validation and site implementation activities were executed using the ABB proprietary software Inferential Modelling Platform.


Data processing is a key task during the development of an empirical model and involves crucial steps.


After the optimal sampling rate was identifi ed to ensure an adequate set of representative records were available for modelling purposes, sophisticated statistical and mathematical techniques were then applied to select the most relevant parameters to be included as input variables for the models. Neural Networks algorithms were used for model fi nalization as they proved to be the most effi cient and robust in terms of accuracy and reliability.


The fi nal PEMS system was integrated with the DCS and other plant automation infrastructure.


To enable the relative accuracy of the PEMS system to be determined, the installed system was then subjected to an Environmental Protection Agency (EPA) assessment and certifi cation process by an authorized third-party company. During this process, emissions estimations by PEMS were compared to values measured by CEMS at different operating conditions. As the performances for each emission were compliant with EPA regulation, the system was certifi ed and accepted by the customer.


Summary – consider your emissions measurement requirements


Obtaining proper, accurate and reliable information about emission levels is crucial both for determining strategies for keeping emissions within regulatory requirements and in the ongoing effort to tackle climate change.


PEMS can take on the duties of a CEMS in certain circumstances, but they are not a direct replacement for all applications. PEMS should instead be considered as a complement to the traditional CEMS. Depending on application and local constraints, best practice may require the installation of a CEMS, PEMS or a combination of both. For stable processes with little variance, a PEMS can do the same job as a CEMS at a fraction of the cost, while in more complex processes they can dovetail effectively to improve accuracy and uptime.


Industrial companies should contact a trusted emission monitoring system supplier to assess the best options for their plants and operations, which may often be a combination of both CEMS and PEMS.


For more information about ABB’s PEMS solutions, visit: https://bit.ly/ABB_PEMSys


Author Contact Details Gregorio Ciario, ABB Measurement & Analytics • Howard Road, Eaton Socon, St Neots, Cambridgeshire, PE19 8EU, UK • Tel: 0870 600 6122 • Email: enquiries.mp.uk@gb.abb.com • Web: www.abb.com/measurement


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