Predictive vs. Continuous Emissions Monitoring Systems

 

PEMS

CEMS

Capital Cost PEMS systems typically cost about 1/2 or less compared to CEMS installations. PEMS typically cost much less than CEMS. The purchase price of a PEMS is even lower if a CEMS is on site to provide QA’d emissions data.
Installation Time A PEMS can be installed in 4-6 weeks.
Installing a PEMS requires the installation of one computer with the software installed & interfaced to the boiler control system. Typically, a one-day installation and start up process.
CEMS are generally delivered in 12-14 weeks.
Installation requires skilled trades (electrical, mechanical, computer) to install ports, probes, umbilical/trays, etc.
Startup Costs PEMS have lower startup costs, normally one day including DAS. CEMS normal start up is 2-4 days, depending on complexity.
Training PEMS require less on-site training.
PEMS training is usually 1 to 1 1⁄2 days plus DAS training.
CEMS vendors typically offer 3-day introductory system training. In-depth training is an additional 5 days. DAS training can be another 2 days.
On-Site Emergency Service PEMS should require no on-site emergency service.
A direct modem to the system takes care of 99% of all service requirements.
On site emergency service for a CEMS is inevitable. Rates run $1200.00 to $1600.00 per day plus portal to portal expenses.
Calibration Gases PEMS do not require EPA protocol calibration gases, piping, wiring, gas regulators or software to operate the auto-calibration sequence. CMC PEMS analyzers do have auto calibration just like a CEMS. CEMS require calibration systems and the ongoing purchase of EPA Protocol Gases.
Cylinders of calibration gases also require safe storage and supplier documentation is necessary. No more demurrage expenses with a PEMS.
Preventative Maintenance PEMS have no ongoing preventative maintenance requirements.  The only maintenance for a PEMS is a periodic cleaning of the PEMS computer. CEMS require daily, monthly, quarterly, semi and annual maintenance. Consumable and spare parts inventories are required to maintain uptime, and generally are equal to 7-10% of the system’s cost. Trained personnel are required to perform maintenance on CEMS, including on-call duties.
Data Availability PEMS have higher data availability which should normally approach 100%.
PEMS uses numerous inputs for a robust data base. Even with a PEMS failure, the data from the DCS inputs for the predictions still reside within the DCS. This data can be retrieved, calculated, and back filled by the PEMS when brought back on line. No down time or missing data should ever be reported.
CEMS typically are considered doing well if they maintain 95% uptime which is a minimum requirement.
If an analyzer fails (NOx, CO or O2 etc.) or a critical component fails the system is consider down and down time is logged. When a CEMS analyzer or critical component fails the system has no capability to retrieve any missing data and data substitution may be required.
Excess Emissions Troubleshooting PEMS can be used to determine the source of excess emissions.
Combustion input parameter(s) that are out of normal range can be identified and alarmed for immediate action and provide a trail to the diagnosis of excess emissions.
CEMS do not provide any insight as to the cause of an excess emission or the ability to facilitate process control or correction of the problem.
CEMS cannot point the operator to the cause or solution of excess emissions.
Obsolescence and service contract costs The PEMS analyzer is not vulnerable to obsolescence. CMC PEMS are continually upgraded for any new regulatory changes or software upgrades through inexpensive ongoing service contracts that typically cost $400 per month. CEMS annual service contracts typically cost $1000.00 to $2500.00 per month plus portal to portal expenses.

NOTE

CMC Solutions has certified many PEMS over the past 15 years. The relative accuracy for PEMS was under 5.0%. This includes the PEMS on gas turbines, natural gas, and BFG fired boilers, natural gas and fuel oil fired boilers, and an ethanol production source. Many CEMS typically find it difficult to achieve a low RA on a regular basis especially following several years of continuous operation and minimal maintenance.

Regulatory acceptance is not an issue in today’s environment. CMC assists in all regulatory communication and documentation required for site installation. The EPA demonstration ending in early 2003, was conducted and endorsed by the EPA so that sources using CMES or installing CMES have a much lower cost alternative that satisfies all the monitoring requirements / regulations. With the advent of the PEMS Performance Specification 16 (PS-16, March 2009) PEMS now have an objective criteria for certifications across the United States.

CMC Solutions guarantees PEMS certification for State, Local, and Federal EPA Part 60/75 regulations. The PEMS purchase has a return on the investment (ROI) of normally less that one year. References provided.