Retrofit Equipment

PLC Control Systems | Metering Pumps | Injection Probes | Molten Sulfur Flowmeter | Dry Sulfur Feeder

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PLC Control Systems

The controls for the flue gas conditioning equipment are state-of-the-art, Allen-Bradley PLC single microprocessor based, specifically designed and manufactured by FGC, Inc. for a user-friendly interface. An SLC-500 with all I/O cards, prewired cables, terminal block modules and PanelView 1000 operator interface are included.

The controller will provide a local control, local operator interface, PID process loops, setpoints and alarms for each system. Local operator interface is provided by an industrial Allen-Bradley color display. It displays operating status, temperatures, alarms, logs and other user-beneficial data, as well as operator data entry for field modification. A 4-20 mA reference signal is provided to support Process Air heater integrated SCR controller. Remote Distributed Control System support is included, allowing remote operation and monitoring via the DCS in the control room.

Factory tested PLC prewired cable assemblies and terminal block modules are included. The I/O module breakout cables and terminal block modules will provide for field connections. A set of terminal blocks will be included for SO3 Production Equipment 120 VAC interlock circuit. The interlock circuit includes the E-Stop pushbutton, low airflow switch, blower starter enable, and air heater enable. The SO3 Production Controls require only a boiler load reference signal to deliver a constant SO3 conditioning feedrate. Many levels of SO3 Controls integration are possible to meet specific customer needs. If requested, FGC will provide for incoming “trim” ratio signals to further determine conditioning federate. At a minimum for system outputs, an analog reference feedback indicates conditioning and a discrete general alarm status is provided.

Terminal Block Modules and Prewired Cable Assemblies

The Production Controls will be supplied ready for DCS integration via ethernet, allowing easy expansion of control features now or in the future. FGC, Inc. will supply, with DCS integration, a detailed list of PLC addresses, tags, scaling, etc. necessary to integrate the controls into a plant DCS system.

SO3 Production Control ladder logic is included. Local operator interface utilizes the graphical PanelView and Keypad. Pushbuttons, lights and annunciator panels are replaced with an all-in-one operator interface. Basic start/stop operator controls, setpoints and process variables are provided on a single Main Process Screen. User interface is intuitive and advanced process details for diagnostics are provided by sub-screens.

TYPICAL AB PanelView Operator Interface

The SO₃ Production Control Software includes controls to support standard SO₃ Production Equipment applications. Standby, Run, Purge and Shutdown pushbutton commands are selectable on the PanelView and eliminate the need for all but an E-Stop pushbutton. The controls may be run in either an Automatic Mode following a boiler load reference signal or in Manual Mode. Automatic Mode will condition flue gas based on a constant PPM feedrate while Manual Mode will deliver a constant lbs./hr of sulfur and is utilized for maintenance during constant boiler loads.

Key process variables and setpoints are displayed on the Main Process Screen. Low airflow, Boiler Load, Process Air Heater Load, Process temperatures, Injection probe temperatures, Alarm log and Process limits are displayed. The logical permissives to allow the system to enter Run are: Airflow, Converter inlet temperature, Injection probe temperature. A logical interlock is included in the software duplicating 120 VAC interlock circuit and can open the 120 VAC interlock circuit.

Advanced features and operator interface screens are included to assist the customer with online SO₃ Production System diagnostics. An alarm log will store the history of unique alarms with a time/date stamp and request acknowledgment. An injection probe diagnostic screen is provided to disable alarms for individual injection probes that are known to have bad thermocouples or readings. SLC-500 I/O card diagnostic screens are provided to show individual I/O status for each card identified by slot and channel to assist in SLC-500 component troubleshooting. The Sulfur Flow vs. Boiler Load chart is included on a separate screen to assist in setting desired PPM Feedrate. Additional screens are included to provide customers detailed status and with advanced SO₃ Production System diagnostic capabilities.

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Molten Sulfur Metering Pumps

FGC, Inc.'s Positive Displacement Sulfur Metering Pumps are offered as a reliable alternative to submersible sulfur pumps and a flow meter. They meter accurately due to the small dead volume, highly incompressible diaphragm seal, and an accurate displacement and check valve system. The integral steam jacketed pump head allows maintenance of check valves without removal of pump from the system or disconnection of process piping, without taking the steam out of service. In addition, this pump design can be retrofitted on out-dated flue gas conditioning systems. FGC, Inc.'s pump assemblies are optimally designed for molten sulfur handling.

Historically, positive displacement molten sulfur pumps were of a 40-year-old design that leaked, froze, jammed and had to be completely removed for routine maintenance. State of the art molten sulfur pumps from Germany have overcome these design problems and have operated reliability in Europe for over twenty years. FGC introduced these pumps in the USA in 1992 and they have provided reliable molten sulfur metering service since.

The benefits of FGC, Inc.'s Positive Displacement Sulfur Metering Pumps are as follows:

• Lower cost over traditional submersible pump/flowmeter combination in retrofit projects.
• Short delivery times for standard pump sizes, typically 8-10 weeks.
• Steam jacketed pump head prevents freezing and jamming.
• Molten sulfur is never exposed to atmosphere.
• Integral check valves may be removed on line while still hot for cleaning.
• No process piping need be disconnected for maintenance, if required.
• Standard 3 phase motor driven with VFD solid state control module.
• Integrated pressure relief valve preventing over pressurization at discharge outlet.
• Mounted at grade level and inside weather protection for the operator.
• 80:1 Turndown ratio

Submersible pumps are an attempt to solve an out dated design problem. However, because the gear pump is operating in a hot abrasive environment (molten sulfur) bearing wear and slippage are problems with only a four year life expectancy. Repair or replacement of a submersible pump requires removing the pump head outside on top to the tank and handling hot parts covered with molten sulfur. When the sulfur cools and freezes, it must be removed to work on the gear head and shaft.

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Injection Probes

FGC Inc.'s SO₃ injection probe assemblies are the ideal choice for both new and replacement applications. FGC, Inc. manufactures injection probes for hot or cold side applications, in either horizontal or vertical duct work. Probes are custom designed per site specific conditions with respect to hot gas piping, duct sizing, flow distribution, and process air flow. Incorporating a flue gas flow study, FGC, Inc. can bias the nozzle location and size to compensate for inconsistent SO₃ concentrations from temperature stratification or poor gas flow. These advantages allow FGC, Inc. to supply injection probes suited to replace many styles of SO₃ flue gas conditioning systems.

Features:

• Stainless Steel hot gas pipe and nozzles prevent corrosion.
• Mounting flange designed to fit existing port or FGC supplied mounting port.
• Probe hot gas flange oriented for connection to SO₃ process air flow.
• Stainless Steel slide plates prevent corrosion and allow thermal expansion.
• Mineral wool 1200° pipe insulation covered with 14 ga. sheathing on inserted section of probe.
• Orifice sizing calculated for maximum air flow without plugging of nozzles.
• Nozzle spacing and quantity calculated for best gas distribution.
• Thermocouple inserted full length of probe to determine temp. at the far end where plugging will first occur.
• Thermocouple can be replaced with zero down time while system is online without removing probe from duct work.

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Molten Sulfur Flowmeter

Many SO₃ Injection systems are operated by metering the displacement of sulfur in the metering pump. Although this is a proven method, it has to be trusted that there is no slippage in the metering pump when metering sulfur flow rates. FGC, Inc. has installed sulfur flowmeters in numerous installations for continuous monitoring of sulfur flow rates.

 

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Dry Sulfur Posimetric Feeder

FGC developed an upgrade component to improve the reliability and accuracy of existing dry sulfur metering systems. The Posimetric feeder replaces the existing problematic auger metering device that is used on dry sulfur feed systems.

The feeder utilizes positive displacement action to feed the sulfur prill with accuracy, offering uniform discharge, consistent volume, and gentle handling. This eliminates the breakdown of material caused by augers, which will reduce plugging in the pneumatic air transfer line. The feeder works by the material locking up between two rotating discs. The discs vary speed to feed the required amount of sulfur to the system as required by the process. The remainder of the SO3 production equipment is reused with this upgrade, maintaining the original capital investment of the equipment.

How It Works

The dry sulfur is consolidated into the feeder (Zone 1) from the storage hopper, once locked up in the feeder, the discs rotate (Zone 2) until they reach an opening at the bottom where the sulfur relaxes (Zone 3) from the locked state and discharges (Zone 4) into the transfer line.

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