Products:  Electric:  HVJ

Model HVJ High Voltage Electrode Boiler

Specification

SPECIFICATION FOR
HIGH VOLTAGE ELECTRODE STEAM BOILERS

Model ________________ ( ______ KW )

Job Name: __________________________________________


Provide PRECISION High Voltage Electrode-Type Steam Boilers as manufactured by PRECISION Boilers, Inc, Morristown, TN for operation on _____ volts, 3 phase, 4-wire, ____ cycle AC. Boiler shall be rated ________ max KW, shall be designed for ____psi, and shall be operated at ____ psig nominal steam pressure.

1.0 GENERAL

The boiler shall be built to ASME Code Section I, Part PEB, and shall consist of a pressure vessel having a central column (header) from which water flows through nozzles toward the electrodes which surround the header. Steam is generated from the surface of the streams of water flowing to the electrodes due to heat generated, in proportion to the water's conductance, as the electrical current flows through the water. Steam is similarly produced in the excess streams of water as it falls from the electrodes downward to the counter electrode (fixed neutral).

Regulation of the boiler output shall be accomplished by controlling the water level in the nozzle header so that a greater or smaller number of nozzles are supplied with water, and thus, a greater amount of water comes into contact with the boiler electrodes. Control of this water level, in turn, is accomplished by varying, via the variable speed circulation pump(s), the water flow to the header in accordance with the respective boiler control -- either to maintain the desired steam pressure or to prevent the boiler from drawing more than the desired kilowatts when the steam requirements exceed the KW setpoint. The boiler electrodes shall be located entirely in the boiler steam space so that stopping of the boiler circulation pump will automatically effect boiler shut-down.

2.0 COMPONENT PARTS

2.1 Boiler Shell

The boiler shall consist of a single vertical vessel constructed and stamped in accordance with the ASME Boiler and Pressure Vessel Code, Section VIII, and shall be National Board inspected with a Manufacturer's Data Report provided. The vessel shall be designed and stamped for a maximum operating pressure of ____ psi for operation at ____ psig.

The boiler vessel shall be fabricated of ASTM SA515-70 or SA516-70 steel. A 12" x 16" manhole shall be provided for access to the boiler interior for internal inspection and repair or replacement of internal parts. All boiler connections greater than 2" pipe size shall be flanged; and all steam connections shall be made to the vertical portion of the vessel to preclude the possibility of leaking steam in the proximity of high voltage electrode terminations. The vessel inner surface shall in-corporate a di-electric barrier above the water level to eliminate foam-induced arcing.
2.2 Central Column Nozzle Header

The central column, through which water is supplied to the nozzles, shall be fabricated of mild steel and shall be supported from the top of the boiler. The jet nozzles shall be in vertical rows and mounted flush with the external surface of the header. Nozzles shall be located so as to maintain uniform phase loadings at all levels of water in the nozzle header. Nozzles shall be free of vanes, to facilitate cleaning.

2.3 Load Regulation

Load regulation shall be accomplished by controlling water flow to the header by VFD of the circu-lation pump(s) operated from the boiler control system. The VFD(s) shall either be located in the boiler control cabinet or in proximity of the circulation pump(s), dependent on the job require-ments.

2.4 Boiler Circulating Pump(s)

The boiler circulating pump(s), located inside the pressure vessel, shall be mixed-flow centrifugal type rated for continuous duty at the boiler operating pressure and temperature, and shall be de-signed for compatibility with low NPSH. The pump shall incorporate a double mechanical seal with water cooling, and shall be removable from outside the vessel. The pump motor shall be 3-phase, ____ cycle, rated for inverter duty, and shall be sized for 100% of maximum pump horsepower requirements, (ie, with cold water at full flow).

2.5 Electrodes

Boiler electrodes shall be of mild steel construction, with replaceable electrode strike plates, and shall be supported by insulators of high grade porcelain. The electrodes shall incorporate dielectric barriers on non-conductive surfaces to eliminate spray-induced arcing. The insulators on the steam side shall be protected from flowing steam by throttling shields. Critical surfaces of the porcelain shall be metallized, and shorting clips shall be used to bridge all air gaps. Steam leak-age paths shall be provided to indicate the condition of the insulator sealing gaskets.


2.6 BOILER CONTROL SYSTEM

2.6.1 Pressure and Load Controls

The boiler control system shall incorporate both pressure control and current load control in the primary control system in a manner which will permit the boiler to maintain the desired steam pressure so long as the steam demand does not exceed a set maximum KW limit; and, at such times as the demand exceeds this set limit, the control shall regulate the boiler output to this maximum. The maximum allowable KW output shall be adjustable by the operator, either locally or remotely, through a range of 0 to 100% of the maximum rated output; and the boiler shall also regulate from 0 to 100% of the maximum rated output as required by the pressure control.

Unless otherwise specified, the control system shall be via PLC with a Touchscreen HMI. The PLC shall include a modem and shall also be able to communicate with the Customer’s DCS/BAS processor as required. System shall be Siemens, or AB at a premium cost.

2.6.2 Load Shed Option

A load shedding circuit, which will operate in conjunction with either a central or local load pro-grammer system, is available as an option.

2.6.3 Limit Controls

The boiler shall be equipped with limit controls to shut down the boiler in the event of occurrence of any of the following conditions:
(1) excess pressure; (2) low water; (3) high water.

In addition, high conductivity and loss of circulation pump cooling water shall be alarmed. Limit controls, such as supervisory relays, overcurrent or ground fault relays (supplied by others), may be connected into the limit control circuit.

2.6.4 Water Level Control

The boiler water level control shall be a single element system incorporated into the boiler master PLC which will operate a normally closed control valve in the feedwater supply line to maintain the flow of feedwater in proportion to the drum water level. Unless otherwise specified, the water level control system shall incorporate a level transmitter, and shall operate a Cashco, Fisher, or equal, pneumatic valve.

2.6.5 Conductivity Control

Conductivity of the water being circulated to the boiler electrodes shall be controlled by an indicat-ing-type conductivity controller which will continuously measure/indicate the conductivity of the water via a bleed off the circulating pump discharge. All water flowing to the conductivity cell will be returned to the boiler to effect minimal energy loss.

Means for isolation of the conductivity cell shall be provided so that normal cell maintenance can be performed with the boiler in operation.

The control will have separately adjustable high and low set points. On actuation of the "high" set point, an automatic boiler blowdown cycle will begin and the HMI will indicate that bleed is in process. Actuation of the "low" contact will be indicated on the HMI and may be used either to sound an alarm or to initiate a chemical feed cycle (neither alarm nor chemical feed pump is sup-plied as standard equipment with the boiler). The conductivity control shall be Rosemount, and shall include the proper conductivity measuring cell.


2.7 BOILER ACCESSORIES

The boiler shall be supplied with the following necessary equipment:

2.7.1 Water Column

A water column shall be provided and shall be suitable for mounting of the water sight gauge and the high and low water cutoffs. A water column drain valve will be provided. The water column connection to the boiler shall be 1" pipe size minimum. The cutoff switches shall be independent of the level control system.

2.7.2 Safety Valves

The boiler will have a minimum of two safety valves, each mounted on a nozzle extending from the vertical portion of the boiler drum. Each valve shall be ASME rated and stamped. Aggregated capacity of the safety valves at their set pressure will not be less than 3.5 pounds per hour per KW input.

2.7.3 Back Pressure Regulating Valve

A back pressure regulating valve will be supplied for installation on the steam outlet of the boiler, and shall be set to control pressure at approximately 5% below normal operating pressure in the event that the steam requirement exceeds boiler output. Control of the back pressure regulating valve shall be incorporated into the boiler master PLC.

2.7.4 Other Accessories

Other accessories in the standard boiler package include:
Standby heater rated ____ KW (____/3/___), steam pressure gauge, boiler water temperature gauge, feedwater stop valve, check valve and 3-valve bypass, one slow-opening and one quick-opening blowdown valves, auto and manual air release valves, steam outlet non-return stop and check valves, steam outlet gate valve with 1” free-blow vent valve, sample cooler, bypass feeder (for electrolyte), and circulation pump cooling water flow switch(es).

2.8 INSULATION, CASING AND TERMINAL GUARDS

The boiler shall be insulated with 4" of foil-faced glass fiber insulation secured to the boiler to pre-vent sagging.

Boiler casing will be 16 gauge steel panels secured to the boiler by means of supports welded to the boiler shell. The boiler high voltage terminals will be enclosed in a protective screen enclosure with "Type D" Kirk-Key interlocks on the access openings to prevent entrance unless the boiler supply switchgear is locked open.

2.9 CONTROL PANEL

The electrical control relays, circulating pump VFD(s), standby heater contactor(s), ____V disconnect and associated push buttons, lights, voltmeter, wattmeter, ammeters (3), and other compo-nents of the boiler control system shall be mounted and prewired in a floor-standing Nema 12 cabinet which will be finished to match the boiler. Control shall be via PLC with a Touchscreen HMI, and should include a UPS to assure continuous operation of the control system during mo-mentary power outages. The control system shall include a telephone jack and modem, as well as communication ports (eg, RS232, RS485, Ethernet, etc) as required for communication with a central DCS/BAS processor. The PLC shall be Siemens, or AB at a premium cost.

Control cabinet wiring shall be of 16 ga stranded copper wire, and shall be color coded. Terminal blocks shall be Marathon or equal; starters, contactors, disconnects, control relays, pilot lights, and pushbuttons shall be Siemens, ABB, or equal; meters shall be switchboard class GE, Yew, Multitek, or Electro Ind. All safety controls shall be in an energized condition during normal boiler operation.

3.0 BOILER ERECTION

The boiler will be shipped partially assembled and will require some field assembly, and comple-tion of electrical, pneumatic and piping connections. The boiler manufacturer shall furnish an erection engineer to supervise the assembly, connection and start-up of the boiler.

Labor and material (except for boiler components) required for erection of the boiler are to be fur-nished by others.


4.0 ELECTRICAL SUPPLY SYSTEM

The boiler will require a 3-phase, 4-wire supply circuit from a wye-connected transformer with the transformer neutral solidly grounded at the transformer and extended by means of a full size insu-lated (600 V) conductor to the boiler neutral lug. The boiler enclosure and control cabinet shall be grounded to the building ground system via property sized equipment grounds. Unless otherwise specified, the motor of the boiler circulating pump and the standby heater will be ____/3/___; and the boiler control circuits will be ____/1/___ from either an external power supply or from a ___/___ control transformer located in the control panel. A 20A ____/1/___ lighting circuit shall be provided to supply lighting and a convenience outlet within the control cabinet.

4.1 High Voltage Switchgear

High voltage switchgear for the boiler supply circuit is to be furnished by others, unless otherwise specified. The switchgear should be a stored energy type rated for the boiler voltage and ampere load, and should be equipped to protect both the branch and feeder circuits, as required, and to protect the boiler from instantaneous overcurrent. The switchgear should also incorporate remote tripping, so it can be opened by the boiler limit controls for safety shutdown, and remote closing, so that the operator can conveniently close the breaker. PT’s, CT's, and an auxiliary switch shall also be provided for use in the boiler control circuit.

NOTE: Fused disconnects or air-magnetic breakers are not recommended for this service.


5.0 CONDENSATE RETURN SYSTEM

The boiler condensate return system, including deaerator and feed pump(s), is to be furnished by others, unless otherwise specified.


6.0 ELECTROLYTE FEED SYSTEM

The boiler shall be supplied with a 4-valve bypass/shot feeder connected in the feedwater line to the boiler to effect electrolyte feed at startup. An automatic electrolyte feed system may also be included and if so shall be furnished by others, unless otherwise specified.


7.0 FEEDWATER TREATMENT

Feedwater treatment equipment, if needed, is to be furnished by others. Feedwater hardness lim-its shall be based on a feedwater analysis and the percent of makeup water required. Conductiv-ity required for the water in the boiler to enable full load operation will be in the 1400 to 2200 mi-cromho/cm range. Feedwater conductivity, however, is recommended at less than 50 mi-cromho/cm for efficient boiler operation, unless blowdown losses can be economically recovered via heat exchangers.