WO2019011935A1

WO2019011935A1 - Arrangement for measurement of fouling deposition and optimal cleaning of water wall tubes in the furnace of biomass firing boilers

Info

Publication number: WO2019011935A1
Application number: PCT/EP2018/068705
Authority: WO
Inventors: Alex DITIATKOVSKY; Anatoly Naftaly Menn
Original assignee: Ditiatkovsky Alex; Anatoly Naftaly Menn
Priority date: 2017-07-10
Filing date: 2018-07-10
Publication date: 2019-01-17

Abstract

A method and arrangement for on-line measurement of fouling deposition on the water wall tubes of a biomass firing boilers is described, which provide protection of the measurement sensor from the hot gases, unburned particles and water/steam jet of cleaning equipment. It is also disclosed the method of optimal cleaning based on real time measurement of fouling and calculation of local heat transfer in different zones of the furnace and its influence on the overall Cleanliness Factor. Furthermore, the method of estimation of the long term rate of erosion of the water wall tubes is suggested which can be implemented in the normally operated boiler, with no need for maintenance during outage.

Description

Arrangement for measurement of fouling deposition and optimal cleaning of water wall tubes in the furnace of biomass firing boilers The present invention relates to arrangements for measurement of fouling deposition and optimal cleaning of water wall tubes in the furnace of biomass firing boilers, methods for measurement of fouling deposition and/or erosion as well as systems for performing the methods. Technical Background

In recent years biomass is intensively exploited as a fuel on power generation units in order to improve ecological parameters of utilities. However usage of biomass on the stations initially intended for coal firing causes additional problems resulted from biomass physical and chemical properties. Namely, alkali oxides presented in biomass are mostly featured in relatively low melting point so that the fouling created at high temperature environment of the boiler furnace appears as a slagging firmly attached to the tube surface. In such a situation cleaning of the fouling became a serious problem because removal of slag requires special equipment capable to produce sig- nificant momentum and pressure on the fouling layer which cannot be achieved with air jet soot blowers. Usually exploited are water lance and water cannon cleaning devices creating a powerful jet of water and steam mixture. These devices are activated periodically, in some predetermined procedure. Unfortunately along with effective removal of fouling, they also cause significant erosion of the water wall tubes, so that reducing of cleaning cycles is very much desirable and optimization of cleaning becomes the real need.

Numerous procedures for so called intelligent soot blowing have been suggested and implemented in the coal firing boilers, but they never have been realized in utility burning biomass. Besides of that most of existing intelligent soot blowing procedures are based on the measurement of integral parameters of the boiler and do not take into account dynamics of real situation in the furnace. More reliable optimization of cleaning can be realized provided it is based on monitoring of reduction of heat transfer due to fouling in different zones of the furnace wall. Recently suggested FTR technology, as disclosed in WO 2014/07280 A1 , allows to implement such an approach, but again till now it was implemented only in the coal firing boilers with air jet soot blowers, mainly because FTR extended part comprising optical elements cannot withstand the forces developing in the course of activation of water/steam mixture exploited for cleaning of biomass. FTR is an acronym introduced by the in- ventors and stands for Fouling Thickness and Reflectivity.

Present invention describes a system which further develops the FTR concept enabling to implement it in the conditions of biomass combustion. Furthermore, proper arrangements of the system suggested below allows also to estimate the rate of long term erosion on the water wall tubes in the course of normal operation of the boiler without need to wait for unit outage.

The problem to be solved is to provide means and methods for measuring fouling deposition and erosion on water wall tubes of furnaces that are used for firing biomass and biomass residues.

Summary of the Invention

The problem is solved by providing an arrangement with the features as described in the main claim. Advantageous embodiments of the arrangement according to the invention as described in depending subclaims.

The problem is also solved by providing methods for measurement of fouling depositions and erosion as described in independent method claims. Advantageous embodiments of the methods according to the invention as de- scribed in depending subclaims.

Furthermore, the problem is also solved providing system for performing the methods according to the present invention as described in independent system claims. Advantageous embodiments of the system according to the in- vention as described in depending subclaims.

An object of the present invention is an arrangement for measurement of thickness and reflectivity of the fouling deposition on the water wall tubes of a furnace, wherein the arrangement comprises:

a first branch, comprising means for measurement of thickness and reflectivity of the fouling deposition, said first branch being arranged to move said means inside and outside of the furnace through an opening between two adjacent water wall tubes of the furnace;

a second branch, said second branch being arranged to open or to close the opening between two adjacent water wall tubes of the furnace, when the said first branch is moved inside or outside of the said opening between two adjacent water wall tubes of the furnace; and

a motion control unit to which said first branch and said second branch are interfaced providing timing and direction of motions of said first branch and said second branch avoiding collision between moving parts of both said branches.

In a preferred embodiment of the arrangement according to the invention said first branch further comprises:

a casing for receiving means for measurement of thickness and reflectivity of the fouling deposition, wherein the casing comprises at least one transparent window;

a slide for guiding said casing;

a transmission mechanism interfaced with said casing for moving said casing along said slide; and

means for motion interfaced with said transmission mechanism.

Also preferred in an embodiment of the arrangement according to the invention, wherein said means for measurement of thickness and reflectivity of the fouling deposition further comprises:

a light source;

a light sensor coupled with an image processing unit;

a standard specimen to be used for calibration purposes; and

optical means for guiding light emitted from said light source to said fouling composition and/or to said standard specimen for measurement of thickness and reflectivity and to said light sensor.

A further preferred embodiment of the arrangement according to the present invention is an arrangement, wherein said optical means for guiding emitted light comprise at least a beam splitter, a mirror, a lens and further means for guiding and/or reflecting said emitted light. In a further preferred embodiment of the arrangement according to the present invention, said second branch further comprises:

a closing plate,

a slide for guiding said closing plate, where said closing plate can be posi- tioned for closing said opening of furnace,

a transmission mechanism interfaced with said closing plate for moving said closing plate along said slide for opening or closing said opening of said furnace; and

means for motion interfaced with said transmission mechanism.

An object of the present invention is also a method for measurement of fouling deposition thickness and reflectivity on different locations on water wall tubes of a furnace, wherein the method comprises the following steps:

a) providing at least one arrangement according to at least one of the preced- ing claims,

b) introducing means for measurement and measuring fouling deposition thickness and reflectivity on different locations on water wall tubes of the furnace,

c) measuring and calculating of local heat transfer in said different locations, d) combining said calculated local heat transfer data,

e) calculating a location of reduced heat transfer at measured locations on water wall tubes, and

f) visualisation of said location of reduced heat transfer.

The calculating is performed by using formula (1 ) as described herein. Using the result of calculation according to formula (1 ) a zone of preferred cleaning is identified. The visualisation of said location can be performed by displaying the result on a monitor or on a printout.

In a preferred embodiment of the method according to the invention the method is further comprising the steps of:

providing at least one cleaning equipment, and

activation of said cleaning equipment, wherein the cleaning is performed in said location of reduced heat transfer that has been visualised in step f). An object of the present invention is also a method for measurement of erosion of water wall tubes of a furnace, wherein the method comprises the fol- lowing steps:

a) providing at least one arrangement according to the invention as described herein,

b) introducing means for measurement and measuring fouling thickness and reflectivity on different locations on water wall tubes of the furnace and visualisation of the measured data,

c) measuring fouling thickness and reflectivity on a reference point on a specimen located outside of the furnace and visualisation of the measured data, d) repeating steps b) and c) after a predetermined time period,

e) comparing measured data in step b) and step c) with data measured in step d),

f) visualisation of said compared data of step e),

g) calculating the rate of erosion, and

h) visualisation said calculated rate of erosion.

The calculating is performed by using formula (2) as described herein. Using the result of calculation according to formula (2) the rate of erosion ER is determined. The visualisation of said rate of erosion can be performed by displaying the result on a monitor or on a printout. It is also preferred that an acoustic signal is generated.

In a further embodiment the method according to the present invention it is preferred that the measurement of erosion according to step b) is performed after a cleaning step has been performed. Especially preferred is the method according to the present invention, wherein said predetermined time period is the time period between two cleaning steps that have been performed at different times.

It is also preferred that the determination of the rate of erosion is measured immediately after a cleaning process.

It is also especially preferred that fouling thickness included in the determination of the rate of erosion is measured immediately after a cleaning process. "Immediately" in the sense of the invention means that fouling thickness and/or rate of erosion will be determined in a time period of 10 seconds to 3 minutes after the cleaning process, especially preferred is a time period of 10 seconds to 1 minute. An object of the present invention is also a system for performing a method according to the present invention as described herein, wherein the system comprises at least one arrangement for measurement of thickness and reflectivity of the fouling deposition on the water wall tubes of a furnace accord- ing to the present invention as described herein and wherein the system further comprises at least one cleaning equipment for performing a cleaning step and/or removing fouling deposition from said furnace.

Especially preferred is the system according to the present invention, where- in the cleaning equipment is selected from soot blowers, water streams and water jets or combinations thereof.

An object of the present invention is also a computer program comprising program code means for performing all the steps of any one of the methods for measuring fouling deposition and/or erosion according to the present invention and/or running and/or operating and/or actuating the arrangement according to the present invention and/or the system according to the present invention when said program is run on a computer. An object of the present invention is further a computer program product comprising program code means stored on a computer readable medium for performing the methods for measuring fouling deposition and/or erosion according to the present invention and/or running and/or operating and/or actuating the arrangement according to the present invention and/or the system according to the present invention when said program product is run on a computer.

Brief description of the drawings

Fig. I shows the concept of dual motion arrangement.

Fig. 2 demonstrates schematics of the FTR sensor when it is moved into the furnace.

Fig. 3 demonstrates schematics of the FTR sensor when it is moved out of the furnace.

Fig. 4 explains the procedure of calculating the erosion rate basing on meas- ured data. Description of Embodiments

As described herein above, the main object of the present invention is an arrangement that allows to introduced the measuring device into the furnace and to withdraw the measuring device from the furnace immediately after the measurement has been performed. This will reduce damage on the measuring device as the measuring device is not subjected permanently to the corrosive and hot conditions inside the furnace. As the measuring requires only a short time period, the measuring device is not intensively subjected to the conditions inside the furnace.

In other words, one object of the present invention is a double motion arrangement for measurement of thickness and reflectivity of the fouling deposition on the water wall tubes of the furnace of the biomass firing boiler providing protection of the measurement sensor from hot gasses, unburnt particles and jet of water/steam cleaning equipment, which arrangement includes;

(i) the first branch moving sensor inside and outside of the furnace through the opening between two adjacent tubes;

(ii) the second branch closing the opening when the sensor is moved by the first branch out of the furnace;

(iii) motion control unit to which both branched of the arrangement are interfaced providing proper timing and direction of both motions and avoiding collision between moving parts.

According to the present invention an arrangements is preferred, wherein the said first branch comprises;

(i) the light source which may be selected from laser diode or a LED or other suitable light sources known in the art;

(ii) optics of illuminating beam which creates the light spot on the surface of the fouling or the surface of the cleaned tube;

(ii) imaging optics creating the spot image on the surface of CCD or other suitable image sensor known in the art;

(iv) the image processor to which video sensor is interfaced and where all calculations of measured thickness and reflectivity are performed;

(v) the standard specimen calibrated in advance in the lab with respect to its reflectivity and located in a constant position relative to the tube. According to the present invention an arrangement is also preferred, wherein the said second branch comprises:

(i) the closing plate;

(ii) the slide limiting the motion of the closing plate

(iii) transmission between the motion source (the motor or pneumatic valve) and the closing plate enabling proper motion of the closing plate.

Another object of the present invention is a method of optimal cleaning based on real time measurement of fouling thickness and reflectivity followed by calculation of local heat transfer in the locations of FTR devices and finding the maximal influence of reduced heat transfer on the Cleanliness Factor, as defined by formula (1 ) as given below.

Another object of the present invention is a method of direct measurement of erosion of the water wall tubes in a furnace with firing biomass or other solid fuel based on measurement locations of the tube surface just after cleaning relatively to the location of the reference point (the light spot on the surface of standard specimen) and calculation according to the formula (2) as given below.

As it is known, FTR technology is based on imaging onto electro-optical detector a light spot created by the FTR optics, first on the surface of the water wall tube and then on the surface of a standard specimen included in the system but does not affected by fouling deposition. The measurements are car- ried out while the boiler is normally operated and therefore the high temperature gases and unburnt components of fuel may affect and even damage the FTR optics. Even more dangerous for FIR sensor is water/steam mixture activated while cleaning of such fuel as biomass is activated. The dual motion arrangement described below enables to avoid this problem and to protect FTR sensor from possible damage. The concept of suggested arrangement is depicted on Fig. 1. The water tubes 1 of the furnace wall are usually connected to each other by metal diaphragm where the opening 2 is created through which the extended part of the FTR sensor is moving periodically in and out from the furnace. It is carried out by the first branch of the dual mo- tion arrangement. This branch comprises the extended part 4 attached to the slide 6 activated by transmission mechanism 7 with means 8 for horizontal motion. While moving out of the furnace the FTR sensor is stopped far enough from the opening 2. To assure that any thermal or mechanical contact with hot gases or fouling components or jet of cleaning water /steam mixture is avoided along with removal of FTR from the furnace the second branch of dual motion arrangement is activated. It comprises the closing plate 9 moving along vertical slide 10 by transmission mechanism 1 1 with means 12 for vertical motion. Activation of both branches of the arrangement are controlled by the motion control unit 13 which provides motion in proper directions of each branch, one after another, with a small delay between them and avoiding any collision and mismatch between moving parts.

The means 8 and 1 1 activating two motions could be electrical motors or pneumatic valves or any other arrangements provided necessary motion in two directions. Also the motion in vertical direction in the second branch was chosen here just as an example - it could be any other motion providing the closing of the opening between measurement cycles of the first branch.

When the closing plate 9 is removed from the opening 2 the first branch of the arrangement perform measurement of two most important parameters of the fouling- deposition thickness and reflectivity. It is done in two steps - first the extended part is moved into the furnace, as shown on Fig. 2, creating the light spot image on the fouling surface and registering its position and intensity on the detector 18 surface, and then, on the second step, the extended part is moved out of the furnace (see Fig. 3) creating the spot on the surface of the standard specimen 20 and registering position and intensity of this second spot. (On Fig. 2 the closing plate, removed from the opening, is not depicted). In both positions, in and out of the furnace, the light spot is originated in the light source 17 (it could be laser diode or LED) followed by mirror 16. The illuminated beam and the reflected (scattered) beam pass through the transparent windows 5 whereas the imaging beams are created by the lens 14 and beam splitter 15 on the video sensor 18 (CCD or any other type) interfaced to the image processing unit 19. Timing provided by the controller 13 is arranged in such a way that the second step of the first branch operation is done when the second branch close the opening with the closing plate. The same sequence is repeated in each measurement cycle. Once the arrangement described above allows measuring locally parameters of fouling deposition at biomass combustion, reduction of local heat transfer can be estimated using standard methods of heat transfer calculations.

Moreover, local heat transfer data can be combined in a heat transfer model of entire furnace and expressed through the Cleanliness Factors, CF, , of all zones where FTR devices with dual motion arrangement are installed (i = 1 ,2 ... ,n). We define the optimal cleaning as the one which enables at each time t to find the zone which impact on CF is maximal and therefore its cleaning is more effective than cleaning of any other zone. Then the method of optimal cleaning can be suggested when at each chosen moment t the values CF, (t) are calculated, based on measured parameters of local fouling, for all / and

{ max CF. ) = CF_k ^ is found indicating the zone / of preferred cleaning. This indication can be transferred to a manual operator or converted in a digital message transferred to the controller automatically activated the cleaning equipment.

Furthermore, the dual motion arrangement described above allows measur- ing the long term rate of erosion caused by biomass fouling. To do that we have to address position of the water tube surface just after cleaning when the fouling is mostly removed.

Let at time ^tJ the extended part 4 of the first branch is inside the furnace, creating the spot on the (clean) tube surface at point A, and then it is moved outside the furnace creating the spot in point C on the surface of the standard specimen 20.The images of those spots onto the video sensor 18 are shown on the Fig.4 where is the distance between two images in pixels. Let that at some other time ^T: the extended part 4 illuminates the tube surface (again clean from the fouling) at point B different from A, if erosion was developing.

The spot on the standard specimen remains at the same point C (the specimen is inside the device and is not subjected to erosion). When erosion is increasing the thickness of the tube wall decreasing and the spot B on the tube surface moves to larger distance from A which causes corresponding change of image location on the detector 18. Repeating measurements in a number n of time intervals along some long time period allows to estimate the rate of erosion ER as following

ER = Cfi_: - 3₀) CT_: - T₀)_Y where K is the calibration factor which takes into account dimension of the detector pixel element, geometry of the incident light beam with regard to direction of growing erosion (usually it is direction of tube radius coming to the location of the light spot).

In order to run or operate or actuate the arrangement or the system according to the invention as described above means for receiving, transmitting, measuring and/or calculating data will be further provided. Such means comprise sensor and actor technology, computer technology and data transfer technology as known in the art. The said technology is at least coupled with motion control unit 13 and image processing unit 19 and cleaning equipment as known in the art. A computer program code and a computer program product according to the invention is present in order to perform the method of the present invention as described above and to control the arrangement and the system according to the present invention. The program code also comprises code for processing mathematical formulas (1 ) and (2) as described above in order to calculate the cleanliness factors CF and the rate of erosion ER.

Reference Signs List

1 water tubes

2 wall

3 opening

4 extended part

5 transparent window

6 slide

7 transmission mechanism

8 means for horizontal motion

9 closing plate

10 vertical slide

1 1 transmission mechanism

12 means for vertical motion

13 motion control unit

14 lens

15 beam splitter

16 mirror

17 light source

18 video sensor

19 image processing unit

20 standard specimen

A tube surface point

B tube surface point

C standard specimen point

Claims

1 . An arrangement for measurement of thickness and reflectivity of the fouling deposition on the water wall tubes (1 ) of a furnace (2), wherein the arrangement comprises:

a first branch, comprising means for measurement of thickness and reflectivity of the fouling deposition, said first branch being arranged to move said means inside and outside of the furnace (2) through an opening (3) between two adjacent water wall tubes (1 ) of the furnace; a second branch, said second branch being arranged to open or to close the opening (3) between two adjacent water wall tubes (1 ) of the furnace (2), when the said first branch is moved inside or outside of the said opening (3) between two adjacent water wall tubes (1 ) of the furnace (2); and

a motion control unit (13) to which said first branch and said second branch are interfaced providing timing and direction of motions of said first branch and said second branch avoiding collision between moving parts of both said branches. 2. The arrangement according to claim 1 , wherein said first branch further comprises:

a casing for receiving means for measurement of thickness and reflectivity of the fouling deposition, wherein the casing comprises at least one transparent window (5);

a slide (6) for guiding said casing;

a transmission mechanism (7) interfaced with said casing for moving said casing along said slide (6); and

means for motion (8) interfaced with said transmission mechanism (7). 3. The arrangement according to claim 1 or 2, wherein said means for measurement of thickness and reflectivity of the fouling deposition further comprises:

a light source (17);

a light sensor (18) coupled with an image processing unit (19);

a standard specimen (20) to be used for calibration purposes; and optical means for guiding light emitted from said light source (17) to said fouling composition and/or to said standard specimen (20) for measurement of thickness and reflectivity and to said light sensor (18).

4. The arrangement according to claim 3, wherein said optical means for guiding emitted light comprise at least a beam splitter (15), a mirror

(16), a lens (14) and further means for guiding and/or reflecting said emitted light.

5. The arrangement according to at least one of the preceding claims, wherein said second branch further comprises:

a closing plate (9),

a slide (10) for guiding said closing plate (9), where said closing plate (9) can be positioned for closing said opening (3) of furnace (2), a transmission mechanism (1 1 ) interfaced with said closing plate (9) for moving said closing plate (9) along said slide (10) for opening or closing said opening (3) of said furnace (2); and

means for motion (12) interfaced with said transmission mechanism (1 1 ). 6. A method for measurement of fouling deposition thickness and reflectivity on different locations on water wall tubes of a furnace, wherein the method comprises the following steps:

a) providing at least one arrangement according to at least one of the preceding claims,

c) measuring and calculating of local heat transfer in said different locations,

d) combining said calculated local heat transfer data,

f) visualisation of said location of reduced heat transfer. 7. The method according to claim 6, further comprising the steps of:

providing at least one cleaning equipment, and activation of said cleaning equipment, wherein the cleaning is performed in said location of reduced heat transfer that has been visualised in step f).

8. A method for measurement of erosion of water wall tubes of a furnace, wherein the method comprises the following steps:

a) providing at least one arrangement according to at least one of the claims 1 to 5,

c) measuring fouling thickness and reflectivity on a reference point on a specimen located outside of the furnace and visualisation of the measured data,

d) repeating steps b) and c) after a predetermined time period, e) comparing measured data in step b) and step c) with data measured in step d),

f) visualisation of said compared data of step e),

g) calculating the rate of erosion, and

h) visualisation said calculated rate of erosion.

9. The method according to claim 8, wherein the measurement of erosion according to step b) is performed after a cleaning step has been performed.

10. The method according to claim 8 or claim 9, wherein said predetermined time period is the time period between two cleaning steps that have been performed at different times.

1 1 . A System for performing a method according to at least one of the

claims 6 to 10, wherein the system comprises at least one arrangement for measurement of thickness and reflectivity of the fouling deposition on the water wall tubes of a furnace according to at least one of the claims 1 to 5 and wherein the system further comprises at least one cleaning equipment for performing a cleaning step and/or removing fouling deposition from said furnace.

12. The system according to claim 1 1 , wherein the cleaning equipment is selected from soot blowers, water streams and water jets or combinations thereof.

13. A computer program comprising program code means for performing all the steps of any one of the claims 6 to 10 and/or running and/or operating and/or actuating the arrangement of any one of the claims 1 to 5 and/or the system of any one of the claims 10 to 12 when said program is run on a computer.

14. A computer program product comprising program code means stored on a computer readable medium for performing the method of any one of the claims 6 to 10 and/or running and/or operating and/or actuating the arrangement of any one of the claims 1 to 5 and/or the system of any one of the claims 10 to 12 when said program product is run on a computer.