DMA De-Superheater Instruction Manual

Instruction Manual Form 5296 April 2001

Design DMA and DMA/AF

Design DMA and DMA/AF Mechanically Atomized Desuperheaters Contents Introduction

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Scope of Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Principle of Operation Installation

1 1 1 2

.................... 2

................................. 3

Maintenance

............................... 6 Servicing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Parts Ordering . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7 W6298 / IL

Introduction

Figure 1. Design DMA/AF Mechanically Atomized Desuperheater

Scope of Manual This instruction manual includes installation, maintenance, and operation information for the Design DMA and DMA/AF mechanically atomized desuperheaters.

nozzle and 10:1 with the AF nozzle). These ruggedly constructed devices are capable of maintaining final temperatures to within 6 to 8_C (10 to 15_F) of saturation.

Only personnel qualified through training or experience should install, operate, and maintain a Design DMA and DMA/AF desuperheater. If you have any questions about these instructions, contact your Fisher sales office before proceeding.

The desuperheaters come with either a standard fixed orifice type spray nozzle or the AF nozzle, which can give greater turndown with its variable geometry design. Multiple nozzle units are available with the AF nozzle for higher spraywater quantity applications.

Desuperheaters of the mechanical-atomizing type are generally used for applications with near-constant loads. The Design DMA and DMA/AF mechanically atomized desuperheaters (figure 1) were designed for these applications as well as those requiring moderate turndown ratios (that is, up to 3:1 with the standard

D101617X012

Description

The Design DMA and DMA/AF desuperheaters can be installed in pipe headers, elbows, tees, and other similar pipe fittings. They can be installed directly into the header through an opening as small as a standard 3-inch ANSI raised-face flange connection. Installation causes no appreciable pressure loss due to obstruction of flow. The use of multiple AF nozzles allows for optimum turndown ratio, spraywater quantity, and serviceability.

Design DMA and DMA/AF Table 1. Specifications

Steam Line Sizes J 6 to 60-inch Steam Line Connection Sizes J 3, J 4, and J 6-inch ANSI Class J 150, J 300, J 600, J 900, J 1500, and J 2500 raised-face flange Spraywater Connection Sizes J 1, J 1-1/2, and J 2-inch ANSI Class J 150, J 300, J 600, J 900, J 1500, and J 2500 raised-face flange Maximum Inlet Pressures(1) Consistent with applicable Class 150, 300, 600, 900, 1500, or 2500 pressure-temperature ratings per ASME B16.34.

Inherent Rangeability(2) Design DMA: Up to 3:1 Design DMA/AF: Up to 10:1 Spraywater Pressure Required 3.5 to 35 bar (50 to 500 psi) greater than steam line pressure Minimum Steam Velocity Design DMA: 9.1 m/s (30 feet per second) Design DMA/AF: 6.1 m/s (20 feet per second) Maximum Unit Cv (for Spraywater Flow) Design DMA: 3.8 Design DMA/AF: 15.0 Construction Materials Valve Body: J Carbon steel, J Chrome-moly alloy steel (F11, F22, and F91), or J 300 series stainless steel Nozzle: J 303 or J 316 stainless steel

1. Do not exceed the pressure or temperature limits in this instruction manual, nor any applicable code or standard limitations.

2. Ratio of maximum to minimum controllable Cv.

Specifications Specifications for the Design DMA and DMA/AF desuperheaters are shown in table 1.

Principle of Operation The Design DMA and DMA/AF desuperheaters reduce steam temperatures by introducing cooling water directly in contact with the hot steam. By regulating the water quantity, the degree of cooling can be controlled and final temperature maintained.

The rate of vaporization, and/or cooling, is a function of droplet size, distribution, mass flow, and temperature. Steam velocity is critical and should be maintained at 6.1 to 9.1 meters per second (20 to 30 feet per second) as the minimum. Actual minimum steam velocity will vary by application. As steam velocity increases, a longer distance is required to achieve homogeneous mixing and complete vaporization.

In both Design DMA desuperheater nozzle styles, the spraywater quantity is controlled by an external control valve which responds to signals received from the temperature control system. The water passes through the main tube of the desuperheater to the spray nozzle and discharges into the steam line as a fine spray (see figure 2.

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W6310-1

Figure 2. Detail of Design DMA/AF Desuperheater

Design DMA and DMA/AF STEM

Installation

BODY SPRING

WARNING PLUG

SPRAY ANNULUS A7191 / IL

NUT PIN SWIRL CHAMBER

WATER INJECTION HOLES (COMPOUND ANGLED ORIFICES)

Figure 3. Design DMA Desuperheater AF Nozzle

The particular nozzle in the sprayhead is tailored to meet a specific set of operating conditions. The nozzle design optimizes the spraywater particle size so that when combined with reasonably high steam velocity it results in complete vaporization and excellent temperature control. The Design DMA desuperheater uses a fixed geometry nozzle, while the Design DMA/AF desuperheater uses a variable geometry AF nozzle. In the AF nozzle design (see figure 3), water enters the swirl chamber via compound angled orifices, thus creating a rotational flow stream. This flow stream is further accelerated as it is forced up and out through the spray annulus. The cone-shaped plug varies the geometry of the spray annulus using a force balance principle between water pressure and the preload exerted by a helical spring. This variable geometry design sprays a thin hollow cone over a wide range of flow rates, which results in excellent temperature control over a wide range of operating conditions.

Personal injury or equipment damage caused by sudden release of pressure may result if the desuperheater is installed where service conditions could exceed the limits given in table 1 or on the nameplate. To avoid such injury or damage, provide a relief valve for over-pressure protection as required by government or accepted industry codes and good engineering practices.

CAUTION

When ordered, the desuperheater configuration and construction materials were selected to meet particular pressure, temperature, pressure drop, and fluid conditions. Do not apply any other conditions to the desuperheater without first contacting your Fisher sales office.

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Design DMA and DMA/AF 1. Mount the Design DMA or DMA/AF desuperheater in a ’’Tee’’ piece at the desired location in the pipe, in accordance with standard piping practice. The nozzle should be positioned at approximately the center of the pipe (see figure 4 for the proper ‘‘T’’ length dimension).

2. Clean and flush out the cooling water line before connecting to the desuperheater. Use only clean sources of cooling water. Use of clean water decreases wear and prevents clogging of the nozzle by solid particles.

Note Fisher recommends installation of a strainer and an isolating valve on the water line between the desuperheater and the water control valve. Failure to do so may result in clogging of the desuperheater by solid particles, thus hampering temperature control of the steam.

3. A straight run of pipe is required downstream of the desuperheater to ensure complete vaporization of

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cooling water. Consult the desuperheater certified drawing for the required distance of straight pipe.

4. The temperature sensor should be mounted according to the manufacturer’s instructions. Minimum distance to the sensor is 30 feet (9.1 meters) downstream of the desuperheater. This distance changes with higher velocity steam flow and the percentage of spraywater required. Consult the desuperheater certified drawing for this distance.

5. There should be no branching out from the steam line to divide the steam flow between the temperature sensor and the desuperheater.

6. A typical installation is illustrated in figure 5. A temperature sensor (TE) measures changes in temperature and transmits a signal to a remote temperature-indicating controller (TC) or distributed control system (DCS). The output signal from the controller is sent to the positioner on the spraywater control valve. The positioner output signal is piped to the actuator. The actuator strokes the stem/plug of the spraywater control valve, as required, to supply the required cooling water to the desuperheater to maintain temperature setpoint.

Design DMA and DMA/AF

203 (8.0)

MOUNTING FLANGE (ANSI RF FLANGE (WATER) SAME SIZE AND PRESSURE CLASS AS BODY FLANGE)

DIMENSION A mm

Inches

360

14.19

448

17.63

524

mm (INCH)

20.63

D (Nominal Pipe Size), Inches

T mm

Inches

6(1) 8 10 12 14 16 18

273 248 216 279 267 241 216

10.75 9.75 8.50 11.00 10.50 9.50 8.50

20 22 24 >24

267 241 216 216

10.50 9.50 8.50 8.50

1. Design DMA only.

Note: For 6-inch and 8-inch (Design DMA/AF only) mounting flange, add 69.6 mm (2.75 inches) to the A and T dimensions.

For ANSI Class 2500 mounting, consult your Fisher sales office.

Refer to the certified drawing to verify the inside-diameter requirements of mounting for Design DMA/AF.

A5094-1 / IL

INSTALLATION CONFIGURATION (1 GASKET REQUIRED) NOTE: ALL FLANGE BOLT HOLES STRADDLE STEAM PIPE CENTERLINE

Figure 4. Design DMA and DMA/AF Dimensions

TC

FISHER DESIGN DMA DESUPERHEATER

B2317 / IL

Figure 5. Typical Design DMA or DMA/AF Desuperheater Installation

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Design DMA and DMA/AF Table 2. Troubleshooting Guide Problem

Corrective Action

Temperature setpoint is not reached

Check water source availability and pressure

Temperature setpoint is not reached

Check nozzle(s) for plugging

Temperature setpoint is not reached

Make sure that steam saturation pressure is not above setpoint

Temperature setpoint is not reached

Check to ensure full actuator stroke is reached on the spraywater control valve

Temperature setpoint is not reached

Check for proper orientation of nozzle in steam flow

Temperature is below setpoint

Check temperature control loop - reset

Temperature is below setpoint

Check nozzle for fouling/poor spray pattern - clean/replace

Temperature is below setpoint

Check temperature sensor location - relocate per guidelines

Temperature is below setpoint

Check for proper orientation of nozzle in steam flow

Water in steam line

Check that steam traps are functioning properly

Water in steam line when steam line isolated

Check for proper desuperheater actuator installation

Water in steam line when steam line isolated

Replace desuperheater seat and plug assembly

Maintenance

Servicing When subjected to normal operating conditions, it is unlikely that wear will occur to the desuperheater body or nozzle. During regularly scheduled maintenance, inspect the nozzle for wear or blockage.

If the nozzle(s) appear damaged or blocked, remove the nozzle(s) and clean the internals of the desuperheater before replacing the damaged or blocked nozzle(s) with a new nozzle(s). After replacement of the nozzle(s), replace the anti-rotation tab or tack weld to prevent the new nozzle(s) from unscrewing during service.

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If it is necessary to remove the Design DMA or DMA/AF desuperheater from service, heed the following warning.

WARNING Avoid personal injury or damage to property from sudden release of pressure or uncontrolled process fluid.

Before starting disassembly: D Isolate the desuperheater from process pressure. Relieve process pressure on both sides of the desuperheater. Drain the process media from both sides of the desuperheater.

D Use lock-out procedures to be sure that the above measures stay in effect while you work on the equipment.

Design DMA and DMA/AF Troubleshooting

Parts Ordering

The following guide (table 2) is intended as a basic first line troubleshooting guide. Contact your Fisher sales office for assistance if you are unable to resolve your field operation problem.

Each Design DMA and DMA/AF desuperheater assembly is assigned a serial number which can be found on the mounting flange of the desuperheater.

Refer to the serial number when contacting your Fisher sales office for technical assistance.

The only recommended spare parts for these desuperheaters are the nozzles.

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Design DMA and DMA/AF

Fisher and Fisher-Rosemount are marks owned by Fisher Controls International, Inc. or Fisher-Rosemount Systems, Inc. All other marks are the property of their respective owners.

EFisher Controls International, Inc. 1990, 2001; All Rights Reserved

The contents of this publication are presented for informational purposes only, and while every effort has been made to ensure their accuracy, they are not to be construed as warranties or guarantees, express or implied, regarding the products or services described herein or their use or applicability. We reserve the right to modify or improve the designs or specifications of such products at any time without notice.

For information, contact Fisher: Marshalltown, Iowa 50158 USA Cernay 68700 France Sao Paulo 05424 Brazil Singapore 128461 8 Printed in U.S.A.