Report on the Decamex cleaning of two fin fan banks. Trial at Australian oil refinery. Prepared by Neil Mahoney. May-09

Transcription

1 Report on the cleaning of two fin fan banks Trial at Australian oil refinery Prepared by Neil Mahoney May09

2 Table of Contents Table of Contents... 2 Summary... 3 Introduction... 3 Results... 4 First fin fans... 4 Table 1: Inlet and outlet temperatures of the first bank during clean... 5 Graph 1: Inlet and outlet temperatures of the first bank during clean... 5 Table 2: Air flow measurement for the first bank... 6 Table 3: Total air flow calculation for the first bank... 6 Table 4: Thermographic profiling of the first fin fan bank... 9 Second fin fans Table 5: Air flow measurement for the second bank Table 6: Total air flow calculation for the second bank Table 7: Thermographic profiling of the second bank Conclusions Recommendations P a g e

3 Summary On May 6, 2009, the two fin fan banks at an Australian oil refinery were externally cleaned through the application of the process. Contract Resources carried out the cleaning work during night shift. Introduction The process was used to perform external cleaning on the two fin fan banks. The process is an online external cleaning method where the powder is applied to the fin fans via low pressure compressed air to physically remove fouling material such as soils and debris, and chemically breakdown binders such as hydrocarbon based products. is safe to apply to aluminium surfaces, and is safe to apply while the fin fan bank is online, including while the fan motors are operating. is applied from the bottom of the fin fan bank. The powder and removed debris exhausts from the top of the bank. The powder is readily biodegradable, and poses no health risks. It is recommended that in the areas near the application of the process, that elevated eye protection requirements be enforced. This method of application has been proven to be able to more adequately penetrate fin fan bundles more readily than water or foam applications. This is particularly important with thicker fin fan banks, such as those with more than 5 or 6 tube rows. Figure 1 is a photo showing the chemical and debris from the fin fans exhausting from the top of a fin fan. Figure 1: exhausting from fin fan top This application allows the efficiency of the fin fans to be improved without the requirement for a unit shutdown. As such, if the benefits are proven, it allows for the process to be introduced as part of the regular unit maintenance schedule. 3 P a g e

4 The fin fans cleaned with the process were monitored for the following parameters: 1. Ambient temperature and humidity. 2. Temperature on the inlet and outlet of fin fan bank; 3. Air flow through the fin fan bank; 4. Infrared thermography conducted on the fin fan banks. The advantages of over other methods typically used are the water savings, as this is a dry process, and the chemical is environmentally safe and biodegradable. Other methods used such as water washing and foam application require large quantities of water to be used, and the application of gelling agents, acids and detergents. As a result, the area beneath the fin fan banks must be barricaded against traffic to avoid safety incidents. This nature of external fin fan cleaning makes liquid waste capture difficult, as the liquid waste falls from the fin fan to grade. Some of the chemicals used are also low ph and as a result can result in difficulty in disposal. Some of the chemicals used may not be biodegradable. Results First fin fans The external cleaning on the first fin fan bank commenced at 2015 on May 6, 2009, and the cleaning on the bank of four exchangers was concluded at 0130 on May 7, Excluding setup time, the cleaning of each fin fan took between 30 to 45 minutes to complete. Number 4 fin fan was cleaned first, and the fin fans were cleaned in series, finishing with number 1. Each fin fan in this bank has 8 rows of tubes, and each fin fan has base dimensions of 9410 x 3048mm. The fin fans are constructed with carbon steel tubes with aluminium fins. This bank is induced draft. From inspection of the underside of the fin fan bank, it was observed that fins in various places across the bank have been damaged, with the most apparent areas being across the middle of number 1, the southern area of number 2, the south western section of number 3, and the north eastern section of number 4. At the start of the cleaning of this bank of four exchangers, the ambient temperature was 20.7 o C with a relative humidity of 79%. At the conclusion of the clean, the ambient temperature was 20.8 o C with a relative humidity of 74%. Conditions were consistent through 4 P a g e

5 the duration of the clean, with a recorded drop in relative humidity from 79% to 74% at 2130, measured after the completion of Number 4. Inlet and Outlet Temperatures At the start of the process the inlet temperature to the bank was 69 o C and the outlet temperature was 62 o C. At the completion of the chemical clean, the inlet temperature was 65 o C and the outlet temperature was 49 o C. The temperature readings were taken at the inlet and outlet headers for the fin fan bank. See table 1 for details. Table 1: Inlet and outlet temperatures of the first bank during clean Prior to Cleaning Completion of Cleaning System ID Inlet Outlet Inlet Outlet Time Temperature Temperature Time Temperature Temperature (oc) (oc) (oc) (oc) Number Number Number Number Graph 1: Inlet and outlet temperatures of the first bank during clean Temperature oc Temperature oc Time Inlet Temperature (oc) Outlet Temperature (oc) T 5 P a g e

6 The temperature trend line shows the change in the difference between the inlet temperature and the outlet temperature during the cleaning process. Air Flow through fin fans Air flow measurement was taken prior to the application of and at the completion of the external clean on each fin fan. Measurements were taken from near the centre of the fin fan, using a TSI 8386A Velocicalc anemometer. The same instrument was used to take all air flow measurements. The anemometer had a current calibration certificate. Results are tabulated below. Table 2: Air flow measurement for the first bank System ID Air Flow before (m/s) Air Flow after (m/s) Air Flow Improvement (m/s) Improvement in Air flow (%) Min Max Ave Min Max Ave Min Max Ave Min Max Ave Number % 7.0% 18.9% Number % 16.2% 14.6% Number % 13.9% 19.4% Number % 50.8% 33.3% Based on the dimensions of the fin fans in the bank, this allows for calculation of total air flow, as tabulated below. Table 3: Total air flow calculation for the first bank Total Air Flow Total Air Flow Total Air Flow before after Improvement System ID (m 3 /s) (m 3 /s) (m 3 /s) Ave Ave Ave Number Number Number Number P a g e

7 Digital photographs visual record Below are photographs of the first bank of fin fans prior to cleaning and after cleaning. All photographs have been taken from the underside. No top side photographs are available due to lack of access to the top of the fin fan bank. These photographs display the presence of fouling material present on the tubes and caught between the fins. The photographs were taken using Fuji S3500 4MP camera. Figure 2: Number 1 before cleaning Figure 3: Number 1 after cleaning Figure 4: Number 2 before cleaning Figure 5: Number 2 after cleaning 7 P a g e

8 Figure 6: Number 3 before cleaning Figure 7: Number 3 after cleaning Figure 8: Number 4 before cleaning Figure 9: Number 4 after cleaning Infrared Thermography Infrared thermography was conducted on the fin fans prior to application of the and after external cleaning had been completed. A Testo 8803 V4 proset thermal imager was used to capture images and conduct thermographic analysis on the fin fan tubes. All image capture and analysis was performed from the underside of the fin fan bank as there was no access to the top side of the fin fan bank. Testo s proprietary software was used to analyse and perform a temperature profile of each image. These results are summarised in the table below. 8 P a g e

9 Table 4: Thermographic profiling of the first fin fan bank Temperature before System ID ( o C) Temperature after ( o C) Temperature Change ( o C) Min Max Ave Range Min Max Ave Range Min Max Ave Number Number Number Number Below are the thermographic captures for each fin fan. These allow a visual representation of the distribution of temperature across the fin fan, and allow the areas where fouling is providing an insulating effect to the tubes and fins to be observed. These images also provide a visual representation of the areas between tubes that have been blocked by fouling material. The temperature is highest in the red areas and grading down through yellow with blue/green being the coolest. On some images, a dark blue bar is present. This portion is a strut present on the fin fan. Figure 10: Number 1 before cleaning Figure 11: Number 1 after cleaning 9 P a g e

10 Figure 12: Number 2 before cleaning Figure 13: Number 2 after cleaning Figure 14: Number 3 before cleaning Figure 15: Number 3 after cleaning Figure 16: Number 4 before cleaning Figure 17: Number 4 after cleaning 10 P a g e

11 Second fin fans The external cleaning on the second fin fan bank commenced at 0140 on May 7, 2009, and the cleaning on the bank of two exchangers was concluded at 0215 on May 7, Only number 2 was cleaned as number 1 was out of service. Excluding setup time, the cleaning of the fin fan took 35 minutes to complete. Each fin fan in this bank has 6 rows of tubes, and each fin fan has base dimensions of 9410 x 3048mm. The fin fans are constructed with carbon steel tubes with aluminium fins. This bank is induced draft. From inspection of the underside of the fin fan bank, it was observed that fins have been damaged in the south western section of number 2. At the start of the cleaning of this bank of four exchangers, the ambient temperature was 20.9 o C with a relative humidity of 74%. At the conclusion of the clean, the ambient temperature was 21.3 o C with a relative humidity of 72%. Conditions were consistent through the duration of the clean. Inlet and Outlet Temperatures At the start of the process the inlet temperature to the bank was 70 o C and the outlet temperature was 46 o C. At the completion of the chemical clean, the inlet temperature was 67 o C and the outlet temperature was 42 o C. The temperature readings were taken at the inlet and outlet headers for the fin fan bank. Air Flow through fin fans Air flow measurement was taken prior to the application of and at the completion of the external clean on each fin fan. Measurements were taken from near the centre of the fin fan, using a TSI 8386A Velocicalc anemometer. The same instrument was used to take all air flow measurements. The anemometer had a current calibration certificate. Results are tabulated below. 11 P a g e

12 Table 5: Air flow measurement for the second bank System ID Air Flow before (m/s) Air Flow after (m/s) Air Flow Improvement (m/s) Improvement in Air flow (%) Min Max Ave Min Max Ave Min Max Ave Min Max Ave Number 1 Number % 5.7% 7.5% Based on the dimensions of the fin fans in the bank, total air flow has been calculated, and is tabulated below. Table 6: Total air flow calculation for the second bank Total Air Flow Total Air Flow Total Air Flow before after Improvement System ID (m 3 /s) (m 3 /s) (m 3 /s) Ave Ave Ave Number 1 Number Digital photographs visual record Below are photographs of the second fin fan bank prior to cleaning and after cleaning. All photographs have been taken from the underside. No top side photographs are available due to lack of access to the top of the fin fan bank. These photographs display the presence of fouling material present on the tubes and caught between the fins. The photographs were taken using Fuji S3500 4MP camera. 12 P a g e

13 Figure 18: Number 2 before cleaning Figure 19: Number 2 after cleaning Infrared Thermography Infrared thermography was conducted on the fin fans prior to application of the and after external cleaning had been completed. A Testo 8803 V4 proset thermal imager was used to capture images and conduct thermographic analysis on the fin fan tubes. All image capture and analysis was performed from the underside of the fin fan bank as there was no access to the top side of the fin fan bank. Testo s proprietary software was used to analyse and perform a temperature profile of each image. These results are summarised in the table below. Table 7: Thermographic profiling of the second bank Temperature before Temperature after Temperature Change (oc) (oc) (oc) System ID Min Max Ave Range Min Max Ave Range Min Max Ave Number 1 Number Below are the thermographic captures for each fin fan. These allow a visual representation of the distribution of temperature across the fin fan, and allow the areas where fouling is providing an insulating effect to the tubes and fins to be observed. These images also provide a visual representation of the areas between tubes that have been blocked by fouling material. 13 P a g e

14 The temperature is highest in the red areas and grading down through yellow with blue/green being the coolest. Figure 20: Number 2 before cleaning Figure 21: Number 2 after cleaning Conclusions There was an observed reduction in outlet temperature of the first fin fans of 13 o C, and over the same time period the inlet temperature dropped by 4 o C. This indicates that there has been an increase in cooling capacity through the fin fans. As external weather conditions were stable throughout the clean, it is unlikely that the observed reductions in temperature were due to changes in ambient weather conditions. It is safe to conclude that the drop in outlet temperature is partly due to the reduced inlet temperature, and partly due to the external cleaning. The T on the first bank prior to cleaning was 7 o C, and was 16 o C at the conclusion of the clean. On the second bank, the inlet temperature dropped by 3 o C and the outlet temperature dropped by 4 o C. The T increased from 24 to 25 o C. The observed reduction in outlet temperature, and the increase in T, indicates that when is applied to an entire fin fan bank, that an observable net improvement in fin fan performance is obtained. The temperature observations indicate that second bank, number 2 was less fouled than the other fin fans that were cleaned. 14 P a g e

15 The positive effect on temperature, resulting from the application of is supported by the infrared thermographic observations. Inspection of the images shows that the overall temperature has reduced across the fin fans. The images show that there are still some hot spots present. The thermographic analysis shows that on the first exchanger bank, numbers 1 and 3, the temperatures have reduced. The temperatures on the other fin fans show a slight increase. The range of temperatures on all exchangers has reduced after cleaning. This indicates that fouling material has been removed, allowing a more even temperature profile. The range of temperatures has tightened by between 1.5 to 8.9 o C, with the largest change being reductions in the maximum temperature of the exchanger tubes and fins. Where the temperatures have reduced, this is more than likely due to the heat being generated being dissipated more readily once the insulating effect of fouling material has been removed, and air flow has been increased. The first bank displayed an increase in airflow ranging from a 14.6% to 33.3% increase through the exchangers. The second bank showed an increase of 7.5%, supporting the conclusions from the temperature results, that this exchanger was less fouled than the exchangers in the first bank. The net calculated increase in airflow through the first bank is in excess of 40m 3 /s. Observation of the photographs shows that tubes and fins of the exchangers prior to cleaning have a dull appearance. After cleaning all fins and tubes have a reflected shine from the camera flash. This shine indicates that material fouling the surface has been removed. Figure 1 shows material exiting from the top of the fin fan. This indicates that all tubes have been contacted by the process. It is important to note that as with any external cleaning process, any material fouling the tube internals will not be shifted, and will contribute to reduced performance, particularly with temperature based metrics. We conclude that the process has provided an improvement to the performance of the fin fans cleaned. The main supporting information for this conclusion is the increase in air flow through the banks. There is also evidence from the temperature profiling that indicates that a benefit has been realized through the net reduction in outlet temperatures, and a lower and more even temperature profile across the exchanger tubes. 15 P a g e

16 Recommendations Contract Resources recommend that temperature trend data for the exchangers, for the 24 hours prior to the application of, and for the 24 hours after the application of be obtained, and investigated to see if the same temperature improvement observations that have been made with the instantaneous spot samples can be supported through trends. The analysis of trends will allow observation of unit operational fluctuations, and allow a more complete understanding of the performance benefits obtained. We recommend that the air flow results be compared against design data to allow comparison of the air flow data against the exchanger design. This will allow the calculation of an overall efficiency gain. We recommend that access be provided to the top of the fin fan bank to allow infrared thermographic analysis and photographs to be taken of the top side of exchangers prior to and upon the completion of the clean. This will provide firm evidence that has had positive effect through the entire exchanger. As there is potential for power saving through the reduction of fan motor speed and stress, we recommend that amperage measurements be made on fan motors during future cleans. 16 P a g e