Top Banner
Waste Heat Boilers and Systems WASTE HEAT BOILERS & SYSTEMS OBJECTIVE Upon completion of this lesson, students should be able to: 1. Know the reasons for waste heat recovery from the diesel engine. 2. Know the various layouts for such a WHR plant. 3. Know how to start, stop and operate the EGE safely. 4. Explain how to control the steam evaporation rate from the EG boiler. 5. Explain the reason for soot fire and hydrogen fire 6. Know the problems associated with dry running of the EG boiler. 7. Know how to combat EG boiler fire and control it. LESSON OVERVIEW In a diesel engine vessel the steam and electricity requirement at sea could be met by heat recovery from the engine exhaust gases using a waste heat recovery (WHR) boiler. The lesson discusses various such arrangements including the design and management issues associated with such a plant. REFERENCES Morton, Thomas D, Steam Engineering Knowledge for Marine Engineers (1994) , Thomas Reed Publications Flanagan, G T H, Marine Boilers Question & Answers (2002) Milton, J H and Leach, Roy M, Marine Steam Boilers (1995) SMA/June 2004 1
24

waste heat recovery system

Oct 29, 2014

Download

Documents

Mariappan Na

marine engine waste heat recovery system
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: waste heat recovery system

Waste Heat Boilers and Systems

WASTE HEAT BOILERS & SYSTEMS

OBJECTIVE

Upon completion of this lesson, students should be able to:

1. Know the reasons for waste heat recovery from the diesel engine.2. Know the various layouts for such a WHR plant.3. Know how to start, stop and operate the EGE safely.4. Explain how to control the steam evaporation rate from the EG boiler.5. Explain the reason for soot fire and hydrogen fire6. Know the problems associated with dry running of the EG boiler.7. Know how to combat EG boiler fire and control it.

LESSON OVERVIEWIn a diesel engine vessel the steam and electricity requirement at sea could be met by heat recovery from the engine exhaust gases using a waste heat recovery (WHR) boiler. The lesson discusses various such arrangements including the design and management issues associated with such a plant.

REFERENCES

Morton, Thomas D, Steam Engineering Knowledge for Marine Engineers (1994), Thomas Reed Publications

Flanagan, G T H, Marine Boilers Question & Answers (2002)

Milton, J H and Leach, Roy M, Marine Steam Boilers (1995)

SMA/June 2004 1

Page 2: waste heat recovery system

Waste Heat Boilers and Systems

INTRODUCTIONThe propulsion diesel engine converts the chemical energy of fuel to heat energy by combustion and that energy is then converted to work in -rotating the crankshaft and propel the ship. When considering a heat balance diagram which, by way of example, is shown in Fig. 1 for a nominally rated highly efficient engine version 6S60MC-C (or 6S60ME-C), operating on 80% SMCR (80% of specified maximum continuous rating), the most attractive waste heat source is the exhaust gas heat. Approximately one fourth of the fuel energy comes out as exhaust gas heat. Even though the exhaust gas temperature the last 25 years has decreased about 130°C, from approx. 375°C to approx. 245°C (ISO), as a result of the obtained higher efficiency of diesel engines, exhaust gas boilers are installed on almost all merchant ships of today.

Fig 1 Heat balance for a diesel engine

TYPES OF WASTE HEAT BOILERS

The various W.H.R. Boilers can be broadly divided into two groups, one with I

natural' and the other with 'forced' circulation.

Natural Circulation BoilerThe Natural Circulation Units are normally low capacity units (maximum 2-5 t/h) with a Tank type design. Tubular designs are also possible, but these must be

SMA/June 2004 2

Page 3: waste heat recovery system

Waste Heat Boilers and Systems

positioned at the same elevated Engine Room position together with the Auxiliary boilers.

In many Tank boiler installations, a Composite design is used. Here, different tube banks are allocated for the oil firing and the exhaust gas flow. This enables simultaneous firing on oil as well as running on exhaust gas. The composite marine steam boiler is a combination of an oil-fired steam boiler and an exhaust gas economizer. When the diesel engine is at full load the fuel oil burner only starts if the steam demand exceeds the steam production achieved from the diesel engines exhaust gases.

Fig 2 Mission OC Boiler Fig 3 Smoke tube boiler

Aalborg MISSION™ OC is a 5 tons/hour vertical composite boiler with an exhaust gas section consisting of smoke tubes. The cylindrical shell surrounds the smoke tubes, the furnace, the steam space and the convective section consisting of pin-tube elements. The boiler pressure part is made of well-proven mild steel with elevated temperature properties.

Forced Circulation BoilerThe Forced Circulation Units are more popular and possess better heat transfer potential. Extreme flexibility in their positioning inside the engine room (E.R.) is possible due to the compact size and force circulation through the boilers.

They can either be of the Coil Type or the Tubular Type.

The Coil type has problem in cleaning and maintenance. The Tubular design is more common to-day because of better thermal efficiency, easier cleaning & repair ability and flexibility to control steam generation.

SMA/June 2004 3

Smoke tube type

Page 4: waste heat recovery system

Waste Heat Boilers and Systems

The design of the W.H.R. Unit depends mainly on the available thermal energy at the boiler inlet and may range from a simple tank type unit to a multi-bank tubular design. The exhaust gas boiler system normally used for the production of

saturated steam needed for heating services is shown in Fig. 6. This is a simple, single-pressure steam system in which the exhaust gas boiler consists solely of an evaporator section. The feed water is pumped directly to the oil-fired boiler which is used as a common steam drum for the oil-fired boiler and the exhaust gas boiler. Separate steam drums may also be used, so that one boiler can be run if the other should malfunction. Because of its simplicity and low capital cost, this system is widely used and is often entirely adequate when the steam production is viewed as a means of meeting the steam demand for heating services on the ship. The loss of water from the exhaust gas boiler is in the magnitude of about 1% of the steam production.

SMA/June 2004 4

Fig 4 Miura Exhaust Gas Economiser –external view

Fig 5 Miura Exhaust Gas Economiser- Internal view

Water tube – Tubular type

Page 5: waste heat recovery system

Waste Heat Boilers and Systems

Fig 6 Normal exhaust gas boiler system for steam production Single pressure steam system with evaporator section only

A larger demand for steam in a Tanker or Specialized cargo vessel may require the use of a high capacity auxiliary water tube boiler. A dedicated W.H.R. Unit is also more likely. A big and powerful engine will mean a lot of waste energy. This could then be used to drive a Turbo-Alternator to supply electrical energy and even aid propulsion through appropriate gearing arrangement.

SMA/June 2004 5

Page 6: waste heat recovery system

Waste Heat Boilers and Systems

Fig 7 Special exhaust gas boiler system with turbo generator for electricity production Fig 8 T/Q diagram

SMA/June 2004 6

170 oC

250oC

130oC

165oC

220oC

165oC 165oC

180oC

15oC

Feed water

Page 7: waste heat recovery system

Waste Heat Boilers and Systems

Pinch pointA temperature/heat transfer diagram, a so-called T/Q diagram, illustrates the characteristic temperature course through the exhaust gas boiler. As an example valid for the special exhaust gas boiler system shown in Fig. 7, a T/Q diagram is shown in Fig. 8. The utilization efficiency of an exhaust gas boiler is characterized by its pinch point. The pinch point is the lowest temperature difference between the exhaust gas and the saturated steam, i.e. the temperature difference between the exhaust gas leaving the evaporator section and the saturated steam, see the T/Q diagram in Fig. 8. Normally, the steam pressure will be above7 bar abs. (6 barg) and often equal to 8bar abs. (7 barg), corresponding to a minimum evaporation temperature of 165°C. According to the T/Q diagram the gas outlet temperature, even for a boiler with feed water preheater section, will therefore not be lower than about165°C, when 20°C or above is used as the pinch point. In principle, the pinch point may be considered a measure of how extensive and how efficient the heat utilisation of the exhaust gas boiler is.

Corrosive action of Sulphur & uptake temperature The exhaust gases enter the superheater at a temperature of 250 °C . As they pass through evaporator section their temperature drops to 180 °C and then to about 170°C at outlet from preheater.

However, if any metal surfaces in the uptakes fall below the 'dew point' temperature at which the water vapour in the exhaust gases condense, then any sulphur dioxide or trioxide present in the exhaust gases, formed by the combustion of any sulphur in the fuel, will be absorbed by the water. This results in the formation of acidic deposits on any metal surfaces below 170°C. This acid can cause corrosive attack on mild steel surfaces at temperatures below 138°C, and on cast iron at temperatures below 115°C.

Feed water temperatureThe feed temperatures are also important as the metal temperatures involved are a function of these feed temperatures, being in general some 5°C higher.

It is thus important to maintain these minimum temperature values under all steaming conditions. If the normal feed temperature entering the economiser is about 140°C there is an allowable margin of some 15-20°C, but the feed temperature should never be allowed to fall below the 115°C limit under steaming conditions; if it does, heavy fouling can occur in addition to the corrosive attack, due to soot deposits building up on the acid dew forming on the cool metal surfaces. Thus some means should be provided to maintain the feed temperatures above these minimum values; for example, by supplying extra steam to a deaerator in a system where one of these is fitted.

These points are vital as the gas temperature leaving the economiser, provided it is above the dew point temperature, has little to do with fouling or corrosion as long as the metal temperatures are kept above the minimum value quoted.

The water temperature within the economiser should not be allowed to exceed a temperature 30°C below the corresponding evaporation temperature; this prevents the formation of steam within the economiser.

SMA/June 2004 7

Page 8: waste heat recovery system

Waste Heat Boilers and Systems

A DOUBLE EVAPORATION SYSTEM: CONTAINING WATER TUBE AND TUBULAR WASTE HEAT BOILER

The above system was designed to safeguard the aux. w.t. boiler tubes from early failures. In tankers a w.t. boiler/tubular waste heat boiler utilising an open feed system may develop frequent tube rupture problems due to contamination from air, dissolved salts and rust particles. In the double evaporation system, the water tube boiler is part of the 'primary' circuit and steam produced at the w.t. boiler is fed to a submerged coil in the Steam/Steam Generator that is part of the 'secondary' system. Heat contained in steam produced at the w.t. boiler is given off at the steam/steam generator and the coil return of pure distilled water comes back to the primary w.t. boiler water drum. Water circulating in the primary system, is thus confined within the system without having any chance of being contaminated.

The steam produced at the steam generator is supplied to the saturated steam line. The secondary steam generator is also connected to the W.H.R. Unit. A circulating pump sucks water from the low pressure heat exchanger and supplies to the waste heat unit. Steam from the waste heat economiser is supplied back to the steam generator that then acts as the steam receiver.

The steam pressure at the primary drum could be as high as 30 bars. At sea, steam supply pressure would depend on the waste heat boiler capacity and would vary from 7 - 11 bars.

The system such as the above obviously would be expensive and more complicated and it would be seldom selected unless on a very large tanker with high steam demand.

SMA/June 2004 8

Page 9: waste heat recovery system

Waste Heat Boilers and Systems

SMA/June 2004 9

Page 10: waste heat recovery system

Waste Heat Boilers and Systems

Fig 9 Double evaporation boiler system for a tanker

SMA/June 2004 10

Page 11: waste heat recovery system

Waste Heat Boilers and Systems

Advanced Total Heat Recovery Plant from Wartsila

The proposed Total Heat Recovery Plant consists of a dual-pressure economiser, a multiple-stage dual-pressure steam turbine, a power turbine, an alternator driven by both the steam turbine and the power turbine, feed water pre-heating system and a shaft motor/alternator system (Fig. 10).

Fig 10 Schematic of Total heat recovery plant… Wartsila

Exhaust gas economiserThe exhaust gas economiser consists of a high-pressure part with HP evaporator and superheating section and a low-pressure part with LP evaporator and superheating section. The pressure in the high-pressure steam drum is at about 9.5 bar(g) pressure. The economiser outlet temperature is not less then 160°C to avoid sulphur corrosion in the economiser outlet. With a pinch point of 10 degrees centigrade, a pressure of about 3.8 bar(g) in the low-pressure steam drum is achieved (Fig. 9). Saturated steam is drawn from the HP steam drum for ship service heating.

Fig 11 T/Q diagram for exhaust boiler

SMA/June 2004 11

Page 12: waste heat recovery system

Waste Heat Boilers and Systems

.Operating modes for the Total Heat Recovery Plant are:A. Motor modeThe heat recovery system generates more electrical power than is needed for shipboard service. The surplus electric power is applied in a motor/alternator adding power to the propeller shaft.

B. Alternator modeThe heat recovery system generates less electrical power than is needed for shipboard service. The missing electrical power is generated by the motor/alternator system.

C. Booster modeMore propulsion power is needed than what is available from the main engine. The motor/alternator system acts as motor with the required electrical power being generated by the heat recovery system and the auxiliary engines.

Optional operating mode:

D. Emergency propulsion modeThe main engine is disconnected from the propeller shaft. The ship is then propelled by the shaft motor with power supplied from the auxiliary diesel engines. The system thus offers considerable flexibility in optimising plant operation to minimise operating costs or maximise propulsion power.The number of auxiliary diesel generating sets can be reduced by employing a heat recovery system. The use of these sets is considerably reduced thereby providing a further potential to reduce operating costs.

Fig 12 Process diagram Total Heat Recovery Plant from Wartsila

WASTE HEAT BOILER OPERATION

SMA/June 2004 12

Page 13: waste heat recovery system

Waste Heat Boilers and Systems

Starting

Consider an economizer type single pressure installation getting circulation from the aux. boiler and steam from the EGE go back to the aux. boiler drum for distribution.

Fig 13 Normal exhaust gas boiler system for steam production Single pressure steam system with evaporator section only

a) Make sure that the inspection covers, header hand hole covers, etc. are back in place and that the safety valve is operational & not gagged; checks such as above would be very important particularly after the boiler has undergone some repairs.

b) Close the header drains and open the vent at the outlet end.c) Open the circulating water valves and start circulating water from the aux. boiler drum 30

minutes before the main engine is started; close the vent as water issues.d) Maintain proper water level at the aux. boiler.

CONTROL OF STEAM GENERATION IN THE WASTE HEAT BOILER

The control of steam output or evaporation is necessary to suit the plant demand and this can be achieved in various ways.

1. Elimination of parallel sections of heat exchanger surface.

2. Exhaust Gas By-passing.

SMA/June 2004 13

Page 14: waste heat recovery system

Waste Heat Boilers and Systems

3. Increasing System Pressure to reduce Generation rate.

4. By Dumping Steam.

1. Elimination of parallel sections of heat Exchange Surface

This system was used for a number of years in the early stages of exhaust gas boiler development, but is now largely superseded by the 'Exhaust Gas by-passing' and 'Steam Dump' systems.

Cutting down a tube bank or coil mean reduction in available heating surface and thus steam generation. This is an easily controlled, fast response, inexpensive and low maintenance system and is really a step ahead of the older manually controlled inlet valves for control of steam generation.

Tube rows or banks are controlled by automatic valves, usually pneumatic from a step-controller action that depends on its signal from the master steam pressure controller.

But the elimination of a section of the boiler heating surface from service by closing off the water supply to that section permits the metal temperature of the tubes in the shut-off section to rise to a metal temperature close to the gas temperature. This should be avoided as the practice can lead to combustion of unburned carbon on the boiler surfaces, particularly if the boiler gas side has been dirty.

2. Exhaust Gas By-passing

The use of an exhaust gas by-pass controlled by modulating dampers is the most common method of steam flow control.

The job is accomplished rather simply in case of a tank type boiler by having inlet by-pass damper. For the tubular design, a number of dampers are fitted at the gas outlet, located on spindles which are position parallel to the tubes. The drum pressure is sensed and the damper positioner would regulate the dampers accordingly. The damper in the generating section operates in reverse proportion to the dampers fitted for the by-pass duct, to control the amount of exhaust gas that would be utilized for steam generation.

The above system is widely used for high pressure boiler systems but may present certain problems when used for W.H.R. system. Gas flow control at relatively lower temperature may result in slower response time and difficulty in accurate and finer degree of control. Damper leakage, buckling of spindles and problems at the bearings are some of the possible system shortcomings. In order to minimise damper problems, it is normal to locate the dampers on the outlet side of the exhaust gas boiler where the gas temperatures are lower. This arrangement would however result in a limited amount of steam production, even under full by-pass conditions.

Considering the possibility of 'soot fire' in the system with inlet valve control, the only other system which can ably incorporate automatic control would be the 'gas bypass' system.

SMA/June 2004 14

Page 15: waste heat recovery system

Waste Heat Boilers and Systems

3. Increasing system pressure to reduce generation rate and vice-versa

A system may be designed to run at higher pressure than at which it would normally operate. For example, if the pressure at the w.h.r. unit is made to increase to that of the auxiliary boiler, the output would be reduced by as much as 10%; as the saturation temperature increases with the pressure, the temperature difference between gas and the internal boiler fluid is reduced, which in turn reduces amount of steam generation.

The above system is less encountered as the range of control is limited and the gas temperature from the inlet to the exit is more or less fixed.

4. Steam dump system

This system does not control steam output from the w.h.r. unit as such but whatever excess is generated is dumped through a large surplus valve to a suitably sized condenser. This method should not be considered as one able to control steam generation but is mentioned as being a practical easy solution to operate the plant as per the steam demand.

W. H. R. unit, when connected to the auxiliary boiler which is equipped with an automatic burner light-off system to overcome any shortfall in steam production, would normally be fitted with a surplus valve and a condenser to avoid 'hunting' of the burner unit and allow the burner to operate with a satisfactory minimum level of throughput.

Fig 14 Steam Dump System

SOOT DEPOSITS AND SOOT FIRE

SMA/June 2004 15

Page 16: waste heat recovery system

Waste Heat Boilers and Systems

The ignition of an accumulation of soot, rich in carbon, caused by poor combustion either in port or when operating at low power for prolonged periods, can when supplied with the necessary oxygen be the source of a fire sufficiently intense to melt and burn steel. Air heaters, with their thin steel plates or air tubes and an abundance of oxygen, can, unless kept clean, be very susceptible to this kind of damage.

The underlying causes of the increase in soot fires are linked to a growing reliance on cheaper, low-grade fuel oils, resulting in more soot in exhaust gases. Another problem is the growing number of long-stroke diesel engines, which calls for larger quantities of cylinder lubrication oil, also adding to the soot build-up.

Air heater and pin tube elements are prone to this fire Indicated by very high uptake temperatures of gases Shut off fuel and air supply to burners and close all dampers Keep circulating pump running through EGE Use water jet and not water spray to fight the fire. Prevent soot deposits by promoting good combustion and regular soot blowing and

cleaning.

Hydrogen fireWhen overheating of a superheater due to insufficient steam circulation is very severe, the tube material may ignite at about 700°C and, burning in the steam, produce free hydrogen. The iron will continue burning independently of any supply of oxygen from the air, and the hydrogen produced by the reaction will burn on coming into contact with air. This means that once such a fire has started there are likely to be two fires burning simultaneously, one, iron burning in steam and the other, hydrogen burning in air, the combined fire being self supporting and probably lasting until the supply of steam is exhausted. The conditions necessary for the initiation of a hydrogen fire fortunately rare are generally accepted to be as follows:

Tube metal temperatures of over 705°C. Tubes with some steam content (usually quiescent or of poor circulation). The presence of a catalyst in the form of a carbon ash.

It is important, therefore, that boiler economisers and exhaust gas heat exchangers are kept clean on the gas side to prevent soot fires, and that if defective are either bypassed on the gas side, or if not bypassed have their defective sections properly blanked off, drained and vented.

.

Stages of soot fire

SMA/June 2004 16

Page 17: waste heat recovery system

Waste Heat Boilers and Systems

RECOMMENDED OPERATION PROCEDURE FOR EGE …. MAN B&WIn view of the damage that can be caused by an extensive soot fire in the exhaust gas boiler, it is recommended, during the operation of the ship, to give due consideration to the following:

Normal operating conditionsa) Soot-blowingIf soot-blowing equipment is installed, it is recommended to check its efficiency and adjusting the number of daily soot-blowings accordingly.

b) Preheated feed water during start-up In order to avoid the condensation of some of the gas constituents, preheated feed water should always be used (temperature higher than about 140°C) during start-up and during low load operation, especially if the boiler is not fitted with an on/off by-pass duct/valve which can be activated in these running conditions.

c) Water circulation, correct functioning It should be ascertained that the boiler’s water circulation system and its control system are functioning properly.

SMA/June 2004 17

Page 18: waste heat recovery system

Waste Heat Boilers and Systems

d) Water circulation after engine stopAfter the engine is stopped, the boiler’s water circulating pump should be kept running until the boiler temperature has fallen below 120°C, because wet oily soot may catch fire at temperatures as low as this. On the other hand, it is recommended not to stop the circulating pump in harbour unless the boiler has been checked and is clean.

e) Heavy smoke from engineIf excessive smoke is observed, either constantly or during acceleration, this is an indication of a worsening of the situation. The cause should be identified and remedied. Excessive smoke could be caused by defective fuel valves, a jiggling governor, incorrectadjustment of the governor fuel limiter, or the malfunctioning of one (of two) auxiliary blowers, etc. The boiler should be checked and cleaned if necessary.

Operating conditions in water leakage situationsDnV recently informed about a case where a water leakage was discovered from a water tube type exhaust gas boiler. In order to get to port, the water circulation was shut off. When arriving at anchorage, the exhaust gas boiler overheated, and the crew found that a high temperature soot fire had occurred.

The above case shows how important it is to cool the tubes, i.e. that the water circulating through the tubes always functions correctly, in order to avoid ignition of the soot.In this case, the water circulation could not continue because of the water leakage. Therefore, in such a situation the below actions are recommended.

Actions to be taken prior to dry running:

a) When shutting off the water circulation, the main engine should also be shut down so that the exhaust gas boiler can cool down and any smouldering of soot deposits on the boiler tubes can die out.

b) The heating surface should be inspected carefully for soot deposits, and water washing performed, both for cleaning and cooling.

c) Make every effort to re-establish the water circulation to the boiler and thereby reduce the dry running period to a minimum.

d) Boiler manufacturers allow dry running of exhaust gas boilers only in the case of emergency and with a clean boiler. In addition they emphasize that every possible precaution must be observed to prevent soot fire.

Actions to be taken during dry running:e) Increase the frequency of soot blowing considerably, and perform soot blowing several times prior to manoeuvring.

f) Inspect the boiler frequently and, if any soot is present, then water wash the boiler and increase the soot blowing frequency.

g) The boiler’s instruction manual must be read carefully and its instructions are always to be followed.

COMBATING AND CONTROLLING EGE SOOT FIRE

SMA/June 2004 18

Page 19: waste heat recovery system

Waste Heat Boilers and Systems

On the other hand, if a soot fire does start after all, it is recommended either of the following two types of measures, depending on the level of fire:

Fire level 1, where an initial soot fire has just been discovered:a) Stop the main engine, and thereby the oxygen supply to the fire.

b) Continue operating the water circulating pump.

c) Never use soot blowers for fire fighting, as air will feed the fire with oxygen, and steam will involve a risk of high temperature fire.

d) Stop the air circulation through the engine, and thereby the air supply to the fire, i.e. keep air pressure on the diesel engine’s exhaust valve closing mechanism (closed valves).

e) Water washing, if fitted, may be used to extinguish the fire. This is normally connected to the ship’s fire fighting water system. In a well-run plant any fire that starts will be small, and if the above emergency action is taken immediately, the fire will be damped down quickly, and water circulated by the pump will help keep the tubes cool and reduce any heat damage caused by the fire.

If the soot fire has turned into an iron fire, this can be indicated by a loss ofwater, for example, if the feed water consumption increases very much and/ or if a low level alarm in the steam drum is activated. A temperature sensor (normally max. 400°C) will not normally be able to measure the high temperatures.

Fire level 2, where boiler tubes have melted down:a) Stop the main engine, if it is not stopped already.

b) Stop the circulating water pump.

c) Close valves on the water circulation line.

d) Discharge the (remaining) water from the exhaust gas boiler sections.

e) Cool down with plenty of splash water directly on the heart of the fire.

DnV warns that, if a soot fire has turned into a high-temperature fire (hydrogen/iron fire), care should be taken when using water for extinguishing, otherwise, the fire may become worse unless large amounts of water are applied directly to the heart of the fire. The main aim, when one discovers an initial small fire, is to prevent it turning into a high-temperature fire.

SMA/June 2004 19

Page 20: waste heat recovery system

Waste Heat Boilers and Systems

Prevention of soot fires by cleaning the economiserKeeping the economizers clean will result in a longer lifetime of the plant, better operational economy and most importantly avoiding the risk of soot fires.

To prevent soot file regular cleaning is necessary to remove soot and cylinder oil deposits.

The cleaning system is used after the engine has been stopped, while the circulation keeps the economizer hot. When the washer operates, soot deposits crack from the tubes, bringing back the clean, metallic surface.

The monitor continuously measures pressure and temperature differences across the economizer, indicating the best time for cleaning. It is a precision device that eliminates excessive use of steam for soot blowing, thus slashing operating costs while increasing security onboard. Damage prevention is vital because once an economizer is impaired,the only remaining option is to start up an oil-fired boiler, which – still not counting the off-hire time – will be expensive.

SMA/June 2004 20