THE CHALLENGE

An existing sulfur dioxide (SO₂) analyzer located at grade in an analyzer shelter utilized a conditioned dry sample feed while an O2 analyzer located near the top of the stack utilized a wet sample basis. Both the SO₂ and O₂ analyzers were connected to a programmable logic controller (PLC) for validation controls. Individual O₂ and SO₂ uncorrected concentration values were being measured and connected to the distributed control system (DCS); where they were then corrected using calculations.

The client needed to install a new continuous emissions monitoring system (CEMS) to meet current federal EPA performance and reporting requirements. This new CEMS would report emissions data back to a central data acquisition system for reporting and historizing the data.

THE SOLUTION

M S Benbow & Associates (MSB) was enlisted to provide engineering, drafting and design, system planning, cost estimate planning and construction assistance to enable the client to comply with this new EPA reporting criteria.

The scope of the project included:

• Replacing and upgrading the O₂ analyzer to one that could measure a dry sample basis. This involved removing and blinding the existing in situ connection.
• Installing a new SO₂ sensor/analyzer in existing shelter at grade and connecting the sample feed to an existing system.
• Replacing validation controls (via an existing PLC) with a new CEMS controller/Data Acquisition and Data Handling System to ensure accurate validation functions. The CEMS controller connected to the existing plant analyzer V-LAN network via newly installed Ethernet switch. CEMS historization and reporting requirements would be available via the CEMS server.
• Connecting priority one hardwire alarms to the DCS as well as the analog concentration readings. The other pertinent data was sent to the CEMS server via the Ethernet connection.
• Existing raw SO₂ and O₂ concentration signal wiring to DCS remained in place, and a new corrected SO₂ measurement value was connected to DCS via the new CEMS controller. Various other data points and alarms were sent to the CEMS Data Acquisition Server via the dedicated fiber network.
• Since the old PLC functionality was replaced by the new CEMS controller, the PLC was converted into the new analyzer building alarm system. New interior building monitors (O₂ depletion, smoke alarm) were installed; exterior beacon and siren warned of possible interior hazards; and alarms were hardwired to the DCS.

THE OUTCOME

MSB recommended an additional level of functionality testing to ensure the system would work as intended. This PLC checkout test procedure, in addition to the factory accepted test procedure, allowed for the seamless upgrade, installation and validation of the CEMS system.

In addition to meeting compliance with new federal EPA performance and monitoring requirements, the client was able to incorporate the PLC function into installing new safety measures.