CEMS vs PEMS

CEMS, "Continuous Emission Monitoring Systems" monitor the flue gas exiting to the atmosphere from a boiler, a furnace, or oven. Certain installations are subject to compliance with jurisdictional requirements for emissions at the state or federal level. CEMS are designed to comply with specific regulatory requirements for measuring and collecting data about specifically targeted pollutants, and installed by commercial and industrial plants to ensure operating compliance with applicable EPA or other jurisdictional rules and requirements.

In general concept, a CEMS samples flue gas, measures concentration of targeted pollutants, captures the measurements as data records, stores data records and produces reports of the emissions. CEMS may also incorporate other measurements and functions, such as as measuring and reporting fuel flow, its opacity and the gas moisture content.

CEMS usually have the same primary components.

• Sampling probe 
• Filter 
• Sampling line 
• Sample conditioning 
• Calibration gas 
• Gas analyzers for specific monitoring tasks 

Common targeted measurements include:

• Carbon dioxide 
• Carbon monoxide 
• Airborne particulate 
• Sulfur dioxide 
• Volatile organics 
• Mercury 
• Nitrogen oxides 
• Hydrogen chloride 
• Oxygen
• Liquid or gaseous fuel flow

The US Environmental Protection Agency requires a data acquisition system and handling process to collect and report the data, which CEMS provides. CEMS must operate and provide data continuously in order to assure operational compliance and meet record keeping requirements.

Around the world, air quality standards require various levels of emissions monitoring to assure that excessive levels of harmful chemicals are not spread throughout the environment. The monitoring of emissions involves the application of sensors and processing equipment to provide information regarding the amount of specific pollutants discharged by a plant or process.

A continuous emission monitoring system (CEMS) consists of equipment necessary for determining the emission rate of targeted pollutants, using analyzer measurements and subsequent data processing to provide results in units pertaining to an emission limitation or standard. This type of monitoring system is applicable where required by statute or regulation, but can also be used to provide valuable combustion or process efficiency data to plant operators.

A predictive emissions monitoring system (PEMS) employs an empirical computer model which will relate the inputs of a combustion system (air and fuel) to the emissions produced by the process. Once the model is established for a particular installation, the emissions can be predicted continuously with accuracy in the range of direct measurements used in CEMS. There are instances where this type of system will fulfill governmental compliance requirements, in place of CEMS. PEMS can also be deployed as a complement to a hardware based CEMS. Plant conditions and an engineering evaluation will determine the best implementation of emissions monitoring equipment and systems to meet regulatory requirements and provide the level of risk management needed.

Share your emissions compliance and monitoring requirements with combustion and instrumentation experts. Leverage your own process knowledge and experience with their product application expertise to develop effective solutions.

Rotary and Linear Drives for Damper Control on Combustion Air and Flue Gas Applications

Pneumatic vane damper drive, one of several
variants available.
Image courtesy Rotork

Combustion air and flue gas damper drives fill a critical role requiring safety, accuracy and reliability above all else. It is critical to deploy the best drive technology to maximize combustion efficiency, minimize emissions and reduce installation costs.

Damper Operator (Drives) Types :

Damper drives can be one of three types: pneumatic, electric, or electro-hydraulic, as described below.

• Pneumatic. These damper operators are used whenever controls rely primarily on compressed air (pneumatic) for moving operators.
• Electric. These damper operators are used whenever controls rely primarily electricity as the power source.
• Electro-hydraulic. These damper operators are the same as the electric type described above, but also have a hydraulic system to position the damper.

A very important part of damper design is determination of damper torque, and sizing and selection of the damper actuator for the maximum torque. Actuator torque should be selected to provide the maximum torque required to operate the damper as well as to provide margin and allow for degradation over the life of the damper. Actuators should be evaluated for damper blade movement in both directions, at the beginning of blade movement, and while stroking blades through the full cycle of movement.

The Goal for Selecting the Best Drive Technology:

Reduced emissions, lower fuel consumption and improved boiler draft control.

Ways to achieve this goal:

• High speed continuous modulation of ID/FD fan and inlet guide vanes 
• Improved modulation and control of secondary air dampers 
• Improved automation and burner management 
• Quick response to plant demand 
• Improved reliability in high temperature environments 
• Precise damper and burner positioning 
• Simple commissioning and diagnostics 
• Low running costs, virtually maintenance free 
• Pneumatic, analog and bus network communications 

For more information, share your requirements and challenges with combustion experts. The combination of your facilities and process experience and knowledge with their application expertise will yield an effective solution.

Predictive Emissions Monitoring Systems

Predictive emissions montioring can be used for meeting
compliance requirements

Around the world, air quality standards require various levels of emissions monitoring to assure that excessive levels of harmful chemicals are not spread throughout the environment. The monitoring of emissions involves the application of sensors and processing equipment to provide information regarding the amount of specific pollutants discharged by a plant or process.

A continuous emission monitoring system (CEMS) consists of equipment necessary for determining the concentration of a gas or particulate matter, or emission rate, using analyzer measurements and subsequent data processing to provide results in units pertaining to an emission limitation or standard. This type of monitoring system is applicable where required by statute or regulation, but can also be used to provide valuable combustion or process efficiency data to plant operators.

A predictive emissions monitoring system (PEMS) employs an empirical computer model which will relate the inputs of a combustion system (air and fuel) to the emissions produced by the process. Once the model is established for a particular installation, the emissions can be predicted continuously with accuracy in the range of CEMS. There are instances where this type of system will fulfill governmental compliance requirements, in place of CEMS. PEMS can also be deployed as a complement to a hardware based CEMS. Plant conditions and an engineering evaluation will determine the best implementation of emissions monitoring equipment and systems to meet regulatory requirements and provide the level of risk management needed.

Share your emissions compliance and monitoring requirements with combustion and instrumentation experts. The combination of your process knowledge and their product application expertise will produce effective solutions.

Comparison of PEMS and CEMS from CTi Controltech

Boiler Efficiency - Small Gains Can Bring Big Savings

Every boiler and steam system has a unique
set of efficiency challenges

There are numerous, actually about a half million, articles on the web about boiler efficiency. Because of the scale of even modest sized boilers, small increases in production efficiency can translate into very substantial monetary savings. Even when you have squeezed that final increment of efficiency from your boiler, a closer look will likely show there is something more you can do.

Increasing boiler and steam system efficiency is not a "one and done" proposition.

Boosting efficiency will undoubtedly involve controlling elements that were not controlled before, or at least controlling them in a more rigorous manner. This means additional instrumentation and controls that were not part of the system previously. Keeping those measurement and control elements in top working order is key to maintaining operating efficiency at stellar levels. The takeaway point here is that...

Higher efficiency operation is likely accompanied by increased system complexity.

Higher efficiency results from operating within a narrower set of conditions. Excess air, combustion temperature, flue gas composition, and more must be continuously monitored and maintained within the necessary envelope to keep the goal efficiency level throughout the varying demand levels on the system. With proper implementation, this additional complexity should not be an undue burden on the system operators. Automation and functionality built into modern measurement and control elements are capable of handling the normal operation and providing notice when conditions adversely vary from predicted or required ranges.

Increased maintenance activity is an integral part of reaping efficiency savings.

Steam systems, whether for heating a commercial building or driving an industrial process, generally involve extensive piping. The consumptive devices serviced by the system, most often where steam becomes condensate, are also part of the efficiency plan. Their productive use of the process steam contributes to overall savings. If an equipment unit, through the efforts of good maintenance and control, can perform its task with 95% of it previous consumption, that is a positive return on the effort and cost expended to boost performance.

Attaining elevated efficiency can result from added equipment, but maintaining high efficiency is a function of attitude and commitment. 

It is important that the managers, supervisors, technicians and contractors responsible for the day to day operation of the system consider efficient operation as a valuable and useful goal. Diligence, discipline, and attention to detail are solid elements of a successful maintenance program.

The US Department of Energy summarizes combustion efficiency on their website.
http://energy.gov/sites/prod/files/2014/05/f16/steam4_boiler_efficiency.pdf

Combustion Efficiency

Operating your boiler with an optimum amount of excess air will minimize heat

loss up the stack and improve combustion efficiency. Combustion efficiency

is a measure of how effectively the heat content of a fuel is transferred into

usable heat. The stack temperature and flue gas oxygen (or carbon dioxide)

concentrations are primary indicators of combustion efficiency.

Given complete mixing, a precise or stoichiometric amount of air is required

to completely react with a given quantity of fuel. In practice, combustion

conditions are never ideal, and additional or “excess” air must be supplied to

completely burn the fuel.

The correct amount of excess air is determined from analyzing flue gas oxygen

or carbon dioxide concentrations. Inadequate excess air results in unburned

combustibles (fuel, soot, smoke, and carbon monoxide), while too much results

in heat lost due to the increased flue gas flow—thus lowering the overall boiler

fuel-to-steam efficiency. The table relates stack readings to boiler performance.

Combustion Efficiency For Natural Gas

Here are some items that can impact boiler efficiency and steam system operating costs. While the list may point you toward some areas that need attention in your system, a good strategy is to consult a combustion specialist and share your concerns and goals for system operation. Their expertise will be an integral part of your good decision making.

• Minimize losses due to leaks throughout the entire connected system.
• Rigorously follow boiler and component manufacturer maintenance schedule recommendations.
• Establish means to provide boiler blow-down when excess accumulation of dissolved solids occurs. Conductivity monitoring can be an effective indicator of dissolved solids.
• Insulate all steam and condensate piping and traps. 
• Establish steam system operation at the lowest effective pressure. Special condensate return accommodations may enhance ability to operate at lower pressure.
• Perform timely maintenance of steam traps in accordance with best practices.
• Use energy recovery units to heat makeup water with waste heat from flue gas.
• Add variable speed drive controls to boiler feed pumps for lower energy consumption and finer control of feed flow.
• Monitor flue gas O2  and temperature levels to determine combustion efficiency and optimize air-fuel ratio.
• Monitor and control air flow and fuel flow using mass flow measuring and control devices for best accuracy.
• On systems with multiple boilers, incorporate load sensing controls that will sequence and optimize the operation of the units in response to demand.

Certainly there is more detail involved in each item listed, plus numerous other potentially energy saving activities. By continuing to properly maintain your existing system and stay informed about new equipment and technology with promising application, you will keep your steam system operating at the top end of its efficiency range.