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Preferred Instruments

Preferred Instruments manufactures microprocessor based controllers, instruments, and electric actuators for combustion and process applications. Preferred Instruments also manufactures oil tank gauging and leak detection equipment. A major component of the Instrument group sales is from control systems integration and personal computer based Supervisory Control and Data Acquisition systems. Preferred Utilities' industrial factory is located in Danbury, CT

Feedwater Center Control System

Boiler feedwater control systems are often the most archaic controls in the steam plant. Poor boiler waterside control contributes to scaling, corrosion, and eventually hot spots and tube failures. The Preferred Feedwater Center can control the surge tank, Deaerator (DA) tank, transfer pumps, and feedwater pumps (on-off or VSD) to improve water quality and feedwater system reliability.

Application

The Preferred Feedwater Center is designed to control the surge tank, Deaerator (DA) tank, transfer pumps, and feedwater pumps (on-off or VSD) to improve water quality and feedwater system reliability.

Overview

Boiler feedwater control systems are often the most archaic controls in the steam plant. Poor boiler waterside control contributes to scaling, corrosion, and eventually hot spots and tube failures. The Preferred Feedwater Center can control the surge tank, Deaerator (DA) tank, transfer pumps, and feedwater pumps (on-off or VSD) to improve water quality and feedwater system reliability.

Better Feedwater Delivery Control

  • “Smart” Pump Sequencing
  • Pump Speed demand based Start-Stop
  • Header Pressure based Start-Stop
  • Lead-Lag Sequence
  • Field Adjustable Parameters

Easy to Use

  • “Overview”, “Alarm”, “Historical Trend” and “Setup” displays enable informed initial setup and process assessment.
  • In a single NEMA 4 wall-mounted enclosure, the Feedwater Center integrates a modem for off-site monitoring, RS485 Modbus communications and 24 VDC power supplies.
  • Optional 10” Operator Interface Touchscreen (OIT) provides graphical overviews as well as Ethernet communication to BAS systems.

Easy to Order, Stock and Field Upgrade

  • Complete system is ordered using a single part number
  • “Plug In” option boards can be used to upgrade a system in the field.

Smart Pump Sequencing: In “headered mode,” pumps are automatically sequenced on/off to ensure that the number of pumps in service meets the demand. If any pump fails to start when called, the Feedwater Center immediately starts another pump to replace the faulted pump. The operator may manually select the lead pump or allow the lead pump to rotate automatically. Additionally, the total number of pumps in service may be set automatically or manually as selected by the operator or all pumps may be shutdown by a building automation system (BAS) ‘enable/disable’ contact input.

Easy Installation & Setup: The Feedwater Center integrates Modbus communications, relays, 24 VDC power supplies, and outdoor reset functions into a single wall mountable controller. Simple menu-style fill-in-the-blanks setup displays minimize commissioning and training time.

LCD Graphic Display: LCD graphic display brings plant overviews, outdoor reset, alarms and event status and setup displays right to the operator’s touch.

Alarms & Event Summary: Up to 200 alarms, system events and operator actions are listed in “first in first out” order with a time/date stamp.  Alarms include system fault, pump failure and both over and under temperature conditions.

Hard Manual Backup: Hardwired control switches and dials provide simple manual control for easy troubleshooting and service. Each pump has an individual speed demand bar graph, a manual speed demand output knob, and an Auto/Manual switch.

Modbus Communication Interface: A factory configured RS485 MODBUS interface is available for building automation or SCADA system monitoring and control.

Optional Features: The Feedwater Center has many features that can be added or removed according to your needs.  This controller was designed to accommodate the needs of any 1-4 pump system.  It is able to run with a surge and a deaerator tank (or one of each, or none).  It accommodates 0-3 transfer pumps and 0-4 feed water pumps. The JC-FWC-FC can be used in headered pump applications as well as individual feed water pumps to each boiler.  The JC-FWC-FC can have all of these following sensors;

Temperature:

  • Condensate Return Line
  • DA Tank

Pressure:

  • DA Tank
  •  Feedwater Header
  •  Steam Header
  •  Make Up Water

Level:

  • 1 DA Tank
  •  1 Surge Tank

Flow:

  • Make Up Water Flow
  • Condensate Return Flow

As well as controlling the speeds of up to three transfer pumps and four boiler feed pumps. The Feedwater Center controls a number of valves in order to maintain levels/pressures/flow rates within the system.

The following valves can be maintained:

  • DA Level Valve
  • DA PSI Control Valve
  • Surge Tank Make Up Water Valve
  • Chemical Feed Pump Valve

This system is easily configured by using the menu driven initial set-up screens. No programming knowledge is required.

Features

  • “Overview”, “Alarm”, “Historical Trend” and “Setup” displays enable informed initial setup and process assessment
  • In a single NEMA 4 wall-mounted enclosure, the Feedwater Center integrates a modem for off-site monitoring, RS485 Modbus communications and 24 VDC power supplies
  • Optional 10” Operator Interface Touchscreen (OIT) provides graphical overviews as well as Ethernet communication to BAS systems

Specification

Application: Supply a fully integrated Feedwater Control system to coordinate the operation of (up to) four VSD controlled Feedwater pumps,  Daearator Level and Pressure Control, (up to) three Transfer Pumps, Water Softener Regeneration and Chemical Feed.  The control system shall be microprocessor-based and suitable for wall mounting.

Pump VSD Modulation: The control system shall provide a PID based control scheme.   As demand increases, the speed of the pump will increase.  Each running pump will modulate in Unison. Modulation signals shall be 4-20 mADC and shall be electrically isolated channel-channel and channel-ground.

Headered Feedwater Pressure Setpoint: The Feedwater Pressure setpoint must be field selectable between Steam Header based or manual.  In steam header based mode, the Feedwater Pressure setpoint must be calculated based on an adjustable deviation from the actual Steam Header Pressure.  In manual, the operator may set the Feedwater Header Pressure Setpoint via a front panel display.

Pump Sequence: The control system shall utilize both Feedwater Header Pressure  (Deaerator Level for Transfer Pumps) and Pump Speed to start and stop the pumps and minimize the total number of pumps in operation. The controller shall start and stop pumps when the Feedwater Header Pressure is outside an adjustable pressure limit band for longer than an adjustable short time delay. To anticipate and minimize header pressure deviations, the control system shall start or stop the next pump if the “lead” pump has been near max or min speed for longer than the adjustable time delay. The control system shall monitor each pump’s flow switch and shall rapidly and automatically replace any pump that fails to prove flow. The lead pump shall either automatically rotate on a time of day / day of week (or month) schedule, or shall be manually selected by the operator.  The control system shall be field adjustable to “per boiler” mode which would run one feedwater pump per boiler.  Additionally, the control system shall be field adjustable to choose between headered or boiler specific piping to determine which pumps should be started.  A 120 VAC Discrete input is to be provided as a Deaerator low level signal that disables all Feedwater Pumps.  A 120 VAC Discrete input is to be provided as a Surge Tank low level signal that disables all Transfer Pumps.

Deaerator Control: The control system shall output a demand signal based on DA Level.  When used with transfer pumps, this is the speed at which the transfer pumps must run.  Without transfer pumps, this would drive a level control valve.  The control system shall drive a Deaerator pressure control valve based on Deaerator Pressure.

Surge Tank Control: The control system shall output a command to a fresh water makeup valve based on surge tank level.  Field adjustable level for valve at 0% open and valve at 100% open shall be provided.

Chemical Feed Control: The control system shall monitor Makeup Water Flow and send that flow signal to a Chemical feed pump.

Soft Water Regeneration Control: The control system shall initiate a soft water regeneration cycle based on time, or upon receiving a soft water alarm.  The operator shall also be able to initiate the soft water regeneration cycle manually.

Monitor Points: The control system shall monitor Deaerator Temperature, Fresh Water Makeup Pressure, Condensate Return Flow and Condensate Return Temperature for display purposes.

Operator Controls, Trends, Indications and Alarms: The control system shall include a 16 line x 40 character (or greater) LCD display for boiler sequence control and status, alarm and event summaries, and setup menus for easy operation, tuning and troubleshooting.  Alarms, events and operator actions shall be logged with Time/Date stamp and English language description.  The control system shall include a minimum of 200-point memory. The control system shall include a minimum 100 x 150 pixel historical trending display or a paperless chart recorder or other videographic hardware to permit logging of at least 32 data points for at least 45 days.  Provide a minimum of 4 “pens” per chart with 8-minute through 24-hour chart “width” selections available.

Communication: The Control System shall have the ability of simultaneously communicating to a Data Acquisition System (DAS), Building Automation System (BAS) or Building Management System (BMS) via RS485 Modbus protocol and to a Personal Computer and an alphanumeric pager via standard telephone lines.  The individual boiler limits, lockout, start/stop, warm standby, and firing rate status shall be readable. Header setpoint, plant firing rate, boiler quantity called to start, boiler selected as lead and all setup parameters shall be readable and writable.

Quality Assurance: The control system shall be manufactured and labeled in accordance with UL508 requirements (CSA C22.2 #14 for use in Canada).  Inspection and labeling shall be supervised by UL or other OSHA approved Nationally Recognized Test Lab (NRTL).  The control system shall be a Preferred Instruments, Danbury, CT, Model JC-FWC-FC.