AU2010201302A1

AU2010201302A1 - Condition based soot blowing system

Info

Publication number: AU2010201302A1
Application number: AU2010201302A
Authority: AU
Inventors: Ivan Budimir; Vladimir MEDIC
Original assignee: IT 1 ENERGY Pty Ltd
Current assignee: IT-1 ENERGY Pty Ltd
Priority date: 2009-04-09
Filing date: 2010-04-01
Publication date: 2010-10-28

Description

1 CONDITION BASED SOOT BLOWING SYSTEM FIELD OF THE INVENTION The present invention relates to a process and method for controlling and removing solid deposits which build up as a result of solid fuel combustion. In 5 particular, the present invention relates to a method or process for monitoring and cleaning the build up of solid deposits in coal fired generators. DESCRIPTION OF THE PRIOR ART Steam generators, hot water generators, and waste heat boilers utilise coal as a fuel source. Coal is a combustible sedimentary rock and is a major fuel that 10 is still used to produce electricity. In 2006 world coal consumption was approximately 6.12 x 1012 tonnes with production expected to increase by approximately 45% in the next 20 years. When coal is used for electricity generation it is first usually crushed and then combusted in a furnace with a boiler. The combustion of the coal creates a 15 number of by-products, ash or fly ash being the most prevalent and this sediment material often builds up on the surfaces of the boiler tubes, which are exposed to the combustion process. This build up of sediment or soot results in the formation of a layer that covers the tubes of the boiler and acts as an insulator to the heat generated from the combustion of the coal. This 20 then reduces proportionally the heat transfer into the tubes and so if the build up of soot or ash is not monitored or controlled then it can become very hard and thick (clinkers) and the removal of this can be very difficult, possibly causing damage to the boiler system. As a consequence, soot build up is therefore directly related to reducing the 25 efficiency of the steam generators and cause them an increase in fuel consumption and energy consumption. If the soot build up is not removed in a controlled way this can lead to erosion of the tubes, fatigue failure of the system caused by damage from cleaning and other associated deficiencies.

2 Due to the design and configuration of steam generators soot build up is often uneven on the tube surfaces and varies dramatically according to the locations of the tubes. As a result designers of coal fired steam generators often introduce a large number of cleaning units so as to cover all exposed 5 surfaces however, the cleaning process is typically initiated at a particular servicing interval time period as it is necessary to temporarily shut down the power station so that cleaning can be carried out. This can take several days to complete and cause considerable disruption. OBJECT OF THE INVENTION 10 It is an object of the present invention to provide a method and/or process to clean coal fired steam generators in an efficient and cost effective manner. It is an object of the present invention to overcome, or at least substantially ameliorate, the disadvantages and shortcomings of the prior art. Other objects and advantages of the present invention will become apparent 15 from the following description, taking in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed. In order to reduce heat transfer losses, increase steam/hot water production and reduce erosion of the tubes, a comprehensive dynamic control is required 20 to monitor the heat transfer efficiency in the boiler tubes and, as appropriate, execute corrective action by activating particular cleaning devices at particular locations within the boiler at a particular time. The optimum efficiency for steady state operation is then a controlled balance between the lowest cost of electricity produced from the fuel used with 25 minimum C02 emission in producing the electricity and then optimizing maintenance cost as a consequence of the operation process. This then overcomes the disadvantages in present cleaning processes where tube erosion or damage to the system can be caused by uncontrolled cleaning.

3 The present invention is a comprehensive dynamic automatic system for soot/ash cleaning inside steam generators and similar combustion devices so as to minimize the loss of heat transfer due to the soot build up on the heat transfer surfaces and to reduce erosion of the tubes which can be caused by 5 frequent/unnecessary cleaning. This, in part, is achieved by selective and controlled activation of particular cleaning devices within the steam generator. This is referred to as condition based soot blowing (CBS). The present invention CBS is carried out by using in-line processes for measurement of temperature, flow and pressure measured at particular 10 locations on the boiler to monitor soot build up and loss of heat transfer. SUMMARY OF THE INVENTION According to the present invention, although this should not be seen as limiting the invention in any way, there is provided a method for optimizing the removal of combustion deposits from the surfaces of a steam generator, 15 including: a. Dividing a steam generator into a plurality of specific segments; b. Each segment having at least one soot cleaning device located thereon or nearby; c. Generating a numerical analysis (ie FEA) model of each 20 segment; d. Monitoring temperature readings on boiler tube surfaces and on web surfaces between tubes; e. Pairs of Thermocouple temperature readings with the numerical analysis to estimate heat transfer through the tubes; 25 f. Determine heat flux measurements in a zone and calculating a cleaning zone index (CIZ) between 0 and 100; g. Generating a segment priority cleaning list (PCLS) based on the cleaning zone index; h. Activating the at least one soot cleaning devices based on the 30 segment priority cleaning list.

4 In preference, the segments are selected from at least one of the following group consisting of: evaporators, superheater, re-heaters, economizers and air pre-heaters. In preference, a segmental heat transfer resistance value (mK/W) is calculated 5 for each segment. In preference, the segmental heat transfer resistance value is a measure of soot build up on the segments. In preference, the method further includes the step of measuring the temperature reading of the boiler tube surfaces after activation of the at least 10 one soot cleaning devices based on the segment priority cleaning list and comparing with the temperature readings in step (b). BRIEF DESCRIPTION OF THE DRAWINGS By way of example, an employment of the invention is described more fully hereinafter with reference to the accompanying drawings, in which: 15 Figure 1 is a schematic of the method of the present invention DETAILED DESCRIPTION OF THE INVENTION The condition based soot blowing method f the present invention is using on line process measurements from the process: temperature, flow and pressure measured at strategic locations to monitor build-up and heat transfer 20 deterioration. Steam Generator may be divided in segments that may be named Evaporators, Superheaters, Reheaters, Economisers and Air Pre-heaters. Segmental Heat Transfer Resistance Rs [mK/W] is calculated online and increase of heat transfer resistance is determined as well as soot build-up for 25 each steam generator'segment is calculated.

5 Change of coefficient R is summarized as a segment cleaning index (CIS). CIS index is measure of heat transfer resistance increase or measure of soot build up in the each segment. Segment Priority Cleaning List (SPCL) is a list where all segments are listed 5 according to their individual segment cleaning index value CIS (m). Each CIS (m) value could be normalized and for example can start from 0 to 100. The segments to be cleaned may have highest index value and are on the top of the list while segments with least heat transfer deterioration, not to be cleaned, are placed on the bottom of the list. 10 In each segment of a stem Generator heat fluxes are calculated from a numerical analysis such as Finite Element Analysis (FEA) model and temperature measurements taken in large number of the tubes in locations in vicinity of cleaning devices. Temperature measurement of the tube surface and web surface (between two 15 tubes) is done with temperature sensors like thermocouples but not limited to them and/or flux meters. Temperature readings from temperature sensing devices placed on the web centre in between the tubes and on the back of the tubes (centerline) and they are coupled with a FEA model and used to estimate heat transfer through the 20 tube wall and soot buildup. Heat Flux metering devices placed on the web in between the tubes are used for calibration and may remain permanently installed in strategic locations for quick calibration. Thermocouples and/or flux meters are strategically positioned in vicinity of 25 soot cleaning devices. Deterioration of heat flux measured by change of temperatures in each zone is monitored and expressed with a calculated Zone Cleaning Index (CIZ).

6 Each segment may have one or multiple cleaning devices and for each cleaning device the Cleaning Zone Index is calculated CIZ (n), based on the temperature measurements. Range for CIZ (n) may be normalized and expressed with 0 (for clean tubes) 5 to 100 (for dirty tubes). Priority cleaning list (PCLZ) for all cleaning devices within the same segment is produced according to the CIZ (n) values. Activation procedure of cleaning devices in CBS is divided in two steps. Step 1. 10 From the Optimiser or segment priority cleaning list (PCLS) select first segment on the list to be cleaned. Step 2 In the selected segment find zone cleaning list (PCLZ) and select first cleaning device to be activated and give command for execution of cleaning. 15 Activation of soot cleaning devices can be through relay systems and PLCs. Direct influence of selected cleaned zone will be monitored and its influence on overall optimum efficiency of the system will be calculated. According to the results further cleaning may be automatically scheduled. Although the invention has been herein shown and described in what is 20 conceived to be the most practical and preferred embodiment, it is recognized that departures can be made within the scope of the invention, which is not to be limited to the details described herein but it is to be accorded the full scope of the appended claims so as to embrace any and all equivalent devices and apparatus. 25 Various modifications may be made in details of design and construction [and process steps, parameters of operation etc] without departing from the scope and ambit of the invention.

Claims

1. A method when used to optimize the removal of combustion deposits from the surfaces of a steam generator, including the steps of: a. dividing the steam generator into a plurality of segments; 5 b. each segment having at least one soot cleaning device located thereon or nearby; c. generating a numerical analysis (ie FEA) model of each segment; d. monitoring temperature readings with thermocouples on boiler 10 tube surfaces and thermocouples on web surfaces between tubes; e. pairing of thermocouple temperature readings with the numerical analysis to estimate heat transfer through the tubes; f. determine heat flux measurements in a zone and calculating a 15 cleaning zone index (CIZ) between 0 and 100; g. generating a segment priority cleaning list (PCLS) based on the cleaning zone index; h. activating the at least one soot cleaning devices based on the segment priority cleaning list. 20

2. The method of claim 1, wherein the segments are selected from at least one of the following group consisting of: evaporators, superheater, re heaters, economizers and air pre-heaters.

3. The method of claim 2, wherein a segmental heat transfer resistance value (mK/W) is calculated for each segment. 25

4. The method of claim 3, wherein the segmental heat transfer resistance value is a measure of soot build up on the segments.

5. The method of anyone of claims 1 - 4, wherein the method further includes the step of measuring the temperature reading of the boiler tube 8 surfaces after activation of the at least one soot cleaning devices based on the segment priority cleaning list and comparing with the temperature readings in step (b).

6. The method when used to optimize the removal of combustion deposits 5 from the surfaces of a steam generator as herein substantially described with reference to the drawings.