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.

Components for Industrial Tank Venting and Flame Arresting

Flammable gas line flame arrester
Image courtesy Groth Corp.

Pressure and Vacuum Relief Valves are protection devices often mounted on a nozzle opening on the top of a fixed roof atmospheric storage tank. Their primary purpose is to protect a tank against rupture or implosion by allowing the tank to breathe, or vent, when pressure changes in the tank due to normal operations.

Pilot Operated Relief Valves serve the same primary purpose as pressure/vacuum relief valves, but with better performance characteristics than weight or spring loaded valves. Lower leakage and better flow performance make a pilot operated valve the solution when the focus is product conservation, expanded tank working band, and reduced fugitive emissions. A pilot operated relief valve provides the maximum available leakage control technology as specified in the Clean Air Act of 1990.

Emergency Relief Valves protect tanks against excessive pressure caused by external fire exposure or flashes within the tank. Emergency relief valves provide higher flow capacity than standard pressure/vacuum relief valves.

Deflagration Flame Arresters are fire safety devices used to protect stored or process media from deflagrations. A deflagration flame arrester can be used on the top of a tank or as an in-line safety device where combustible gases are transported through low pressure pipe lines.

Detonation Flame Arresters provide flame protection in cases where the ignition source pipe lengths are greater than what can be protected with a deflagration arrester.

Blanket Gas Regulators can provide both pressure and fire protection for storage tanks by supplying a blanketing gas which maintains a constant positive pressure in the vapor space of a storage tank. In addition to preventing outside air and moisture from entering the storage vessel, a blanket gas regulator reduces the evaporation of the stored product to a negligible amount, resulting in product conservation and greatly reduced emissions.

Matching the function and capacity of each of these safety valves requires engineering expertise to assure proper operation. Share your requirements with product application specialists, combining your own process knowledge and experience with their product application expertise to develop an effective solution.

Flame control products for industrial fluid operations from CTi Controltech

Reliable Level Switch Technology

Level switches in steam and other fluid systems deliver value by providing reliable service over long periods of time, and under sometimes challenging conditions. The Mercury-Free Level Switch, from Jerguson®, utilizes an external float chamber and a magnetic coupling of the float to the switch mechanism. The three magnet system produces a smooth and reliable snap action that is illustrated in the short video,

Share your fluid control and steam system challenges with combustion and steam system experts, combining your own knowledge and experience with their product application expertise to develop effective solutions.

Electric Actuator for Linear and Quarter Turn Control Valves

Many process control valve installations present the option of selecting either electric or pneumatic actuators as part of the control component train. Pneumatic actuators have been in use for many years, but advances in electric motor design that delivered greater torque and more precise operation have brought electric valve actuators into a prominent market position.

Electric actuators are compact and comparatively self contained, requiring only cable connections and none of the additional devices sometimes needed for a pneumatic installation. There are some points of advantage to consider with electric actuators. Rotork introduced their CVA line of electric actuators almost ten years ago, making it something of a mature product now. Here are some advantageous points about the CVA actuators that likely apply generically as well.

• Setup is accomplished with a Bluetooth enabled device which provides quick calibration of open and closed positions, as well as establishment of valve setup parameters.
• A separately sealed electrical connection compartment keeps motor and mechanical compartment isolated from the environment while electrical connection section cover is removed.
• An on board datalogger records thrust and position data over time for use in asset management and service functions. Data can be downloaded by Bluetooth or transmitted by common protocol to another station.
• Change in setpoint produces a rapid and precise change in valve position with high resolution accuracy and repeatability.
• Actuator can be programmed to move to a preset condition in the event of a loss of electric power. The energy to achieve the failsafe position is stored in the actuator.
• Force balance positioning used in pneumatic valves, with spring force vs. air pressure, has resilience that can result in a change in position of the valve trim in response to a bump in system pressure. Resistance from the gear train on electric drives prevents this movement.
• Static friction of the valve packing and other parts increases the amount of force to intially get the valve moving toward a new position. The additional time required to build air pressure and force to overcome static friction results in delayed valve response, then overshoot of the new setpoint. A combination of a sensor system and the mechanical drive section of an electric actuator eliminates overshoot and delayed response.

Electric actuators can be had in quarter turn and linear versions, with torque ranges suitable for a broad range of process control applications. The datasheet below, from Rotork, provides useful illustrations of the actuator interior, along with additional detail about electric actuators. Share your process control valve requirements and challenges with product application specialists, combining your own process knowledge and experience with their product application expertise to develop the best solutions.

Differential Pressure Transmitter Inferential Applications

Differential pressure transmitter for industrial
process control applications.
Image Courtesy Azbil North America

Differential pressure transmitters are utilized in the process control industry to represent the difference between two pressure measurements. One of the ways in which differential pressure (DP) transmitters accomplish this goal of evaluating and communicating differential pressure is by a process called inferential measurement. Inferential measurement calculates the value of a particular process variable through measurement of other variables which may be easier to evaluate. Pressure itself is technically measured inferentially. Thanks to the fact numerous variables can be related to pressure measurements, there are multiple ways for DP transmitters to be useful in processes not solely related to pressure and vacuum.

An example of inferential measurement via DP transmitter is the way in which the height of a vertical liquid column will be proportional to the pressure generated by gravitational force on the vertical column. The differential pressure transmitter measures the pressure exerted by the contained liquid. That pressure is related to the height of the liquid in the vessel and can be used to calculate the liquid depth, mass, and volume. The gravitational constant allows the pressure transmitter to serve as a liquid level sensor for liquids with a known density. A true differential pressure transmitter also enables liquid level calculations in vessels that may be pressurized.

Gas and liquid flow are two common elements maintained and measured in process control. Fluid flow rate through a pipe can be measured with a differential pressure transmitter and the inclusion of a restricting device that creates a change in fluid static pressure. In this case, the pressure in the pipe is directly related to the flow rate when fluid density is constant. A carefully machined metal plate called an orifice plate serves as the restricting device in the pipe. The fluid in the pipe flows through the opening in the orifice plate and experiences an increase in velocity and decrease in pressure. The two input ports of the DP transmitter measure static pressure upstream and downstream of the orifice plate. The change in pressure across the orifice plate, combined with other fluid characteristics, can be used to calculate the flow rate.

Process environments use pressure measurement to inferentially determine level, volume, mass, and flow rate. Using one measurable element as a surrogate for another is a useful application, so long as the relationship between the measured property (differential pressure) and the inferred measurement (flow rate, liquid level) is not disrupted by changes in process conditions or by unmeasured disturbances. Industries with suitably stable processes – food and beverage, chemical, water treatment – are able to apply inferential measurement related to pressure and a variable such as flow rate with no detectable impact on the ability to measure important process variables.

Share your process measurement challenges with instrumentation specialists, leveraging your own process knowledge and experience with their product application expertise to develop an effective solution.

Industrial Transmitters for Pressure and Differential Pressure from CTi Controltech