1 Introduction The leakage of the pipe is an accident that is more likely to occur in the boiler. After the pipe is perforated, the boiler will not be able to maintain the normal water level and can not be burned normally. This will have a direct impact on the operation and bring economic losses to the owner. The furnace is reported to the local boiler safety supervision department. This paper takes a case of boiler pipe perforation leakage as an example to analyze the causes of such events and gives measures to prevent them from happening. The peak of boiler use in winter is coming. I hope that this article can be used as an example to attract the attention of relevant personnel of relevant units and effectively prevent the occurrence of similar incidents.
2Overview of an imported horizontal internal combustion pyrotechnics fuel-fired boiler with a rated evaporation of 6t/h, rated pressure 1.0Mpa, operating pressure 0.78Mpa, commissioned in June 1997, intermittent operation (accumulated nearly 4 years).
During the routine inspection in May 2008, it was found that there was dripping mark on the lower part of the smoke box behind the furnace, and it was required to stop the operation immediately. After the furnace was cooled, the smoke box was opened, and there was a phenomenon of water seepage in the lower part of the tube plate, and the pot water was drained. On the day of internal inspection, it was found that the pipe was corroded and perforated, and the specific position was the second return inlet from the top to the bottom of the row, from the left to the second, and the water side of the second return pipe was found to be close to the flashback. There is ulcerative oxygen corrosion at the chamber end.
3 Inspection and analysis 3.1 Macroscopic inspection The perforation of the pipe is located near the weld joint between the pipe and the tube sheet. There is a gray-brown corrosion product at the perforated part. After the corrosion product is scraped, it is corroded, and the depth is 2.9mm. The cross-section sample tube was cut by the nearby cutting. It was found that the corrosion of the corrosion pit originated from the outer wall of the pipe and was located beside the weld. The thickness of the bottom of the corrosion pit was obviously thinned, and the thin part of the zui had penetrated.
After the smoke pipe is taken out at the site, it can be seen that except for the perforated part of the pipe, the outer surface of other parts is also obviously scattered with a plurality of pits, and the pit has a layered covering, which is suspected of corrosion products.
Due to the limitation of the means, further chemical composition analysis and metallographic analysis of the extracted pipe section have not yet been carried out. However, since the boiler has been in normal operation for 10 years, it is preliminarily determined that the metallographic structure of the raw material of the pipe is normal, the chemical and mechanical properties are normal, and indirectly Exclude material reasons.
3.2 Data investigation On-site inspection of the product quality certification document of the boiler, found that the boiler product has a complete material certificate and inspection certificate, complete documentation, smoke pipe use in accordance with German TRD201St37.8, specifications φ63.5 × 2.9mm, equivalent In domestic 20# boiler tube (GB3087).
3.3 Operational investigation 3.3.1 The purpose of the steam boiler is to provide daily air consumption in the hotel laundry, heat exchangers for daily hot water through the heat exchanger, and heat source for the winter air conditioning system.
Due to the provision of a backup furnace, the boiler is not operated at full load for a long time. The annual operating state is intermittent use. The total operating period is about 4 months per year. The steam pressure during the operation is maintained at 0.68~0.78Mpa.
3.3.2 The furnace is supplied with water from the building pool. The raw water is municipal water supply. In order to ensure the sanitary standard of the water quality of the pool, the property personnel put the slow-release chlorine balls purchased from the health and epidemic prevention station into the pool, but the residual chlorine in the water was not monitored.
The furnace is equipped with the original US sodium ion exchanger, and it runs normally. The water is tested at the soft water outlet point of the exchanger, and the result is qualified.
The furnace is equipped with a thermal deaerator. For various reasons, the thermal deaerator is in intermittent operation. In 2005, the thermal deaeration was stopped and the chemical deaeration was changed, but the concentration of the dosing was constant all the year and the deionized water quality test was not carried out. .
The boiler reuses the condensate from the steam system. The soft water effluent enters a steel open water tank, and the condensed return water also directly enters the water tank. After the two are simply mixed, the water tank directly supplies water to the boiler. The current feed water temperature averages 40 to 50 ° C, and the Zui height can reach 70 ° C. .
3.3.3 Due to the civil construction of the boiler house, the installation of the sewage discharge expansion vessel and the corresponding pipeline is not perfect, and the regular sewage discharge during the daily operation of the boiler is not complete.
3.3.4 In the summer of 2006, the fuel system was reformed from single fuel to oil/gas. It has been in gas service for nearly one year.
4 Corrosion mechanism and cause analysis Corrosion refers to the damage of metal surface caused by chemical or electrochemical action under the action of surrounding medium. Corrosion damage can be either monolithic or local, and it can be uniform or non-uniform. From the morphology and analysis of the corrosion of the boiler pipe, it can be concluded that the corrosion of the pipe is a local uneven electrochemical corrosion. Specifically, the reason for the corrosion of the pipe is as follows.
4.1 Oxygen corrosion and its causes For boiler pressure components, the water side is mainly electrochemical corrosion, and the fire side (or smoke side) is mainly chemical corrosion. Oxygen corrosion is electrochemical corrosion, mainly due to dissolved oxygen in water. At normal temperature, the dissolved oxygen concentration in water is about 9.1mg / L (1 absolute atmospheric pressure, 20 ° C), while GB1576-2001 "industrial boiler water quality" requires rated steam pressure ≤ 1.0MPa, dissolved oxygen concentration ≤ 0.1mg / L, too High is likely to cause metal corrosion. The mechanism is that iron and oxygen form two electrodes, which constitute an etching battery. In the corrosion battery, the potential of iron is always lower than the electrode potential of oxygen, so iron is the anode of the battery, and the pot water is a polar electrolyte in water. Under the attraction of the polar molecules, a part of the iron atoms on the surface of the steel began to move into the pot water to become positively charged iron ions, while the excess electrons on the steel were negatively charged. If iron ions continue to enter the pot water, pits are gradually formed on the steel sheet (tube), causing corrosion.
Dissolved oxygen in the pot water has a depolarizing effect that exacerbates this process. The strength of depolarization is related to the amount of oxygen, that is to say, the amount of dissolved oxygen determines the strength of corrosion, and the two are linearly proportional. The main factor affecting oxygen corrosion is the concentration of dissolved oxygen in water. Dissolved Oxygen Corrosion As the amount of dissolved oxygen in the water increases and the water temperature increases, the corrosivity becomes stronger.
The boiler has an evaporation capacity of 6t/h. Although chemical deaeration is now used, there is no means to measure the oxygen content, which results in incomplete dehydration of the feed water. Therefore, the pot water must contain a certain concentration of oxygen, and oxygen corrosion is formed after the operation. The macroscopic feature of oxygen corrosion is the formation of ulcerated rust on the surface of the metal. The surface of the ulcer rust is a yellow-brown or brick-red hard shell, and the lower layer is a black powder. After the powder is removed, it will appear as a pit. In this case, the obvious ulcer rust on the perforation of the pipe, the corrosion on the metal surface will locally expand to the depth, and the perforation is gradually formed. It can be confirmed that oxygen corrosion is an important cause of leakage and perforation of the pipe.
4.2 Chlorine Corrosion and Its Causes Chloride ion exchange has a high corrosion rate to metals due to its small chloride ion radius and its typical activated anion, which is more active in the presence of dissolved oxygen. With the operation of the boiler, if the salt content of the pot water increases, the chloride ion concentration increases continuously, and more chloride deposits appear in the bottom of the boiler, the pipe and the water circulation are weak. When oxygen corrosion occurs, the metal is continuously dissolved, and the metal cations in the corrosion pit are continuously increased. In order to maintain the charge balance, the chloride ions in the water continuously migrate into the corrosion pit, so that the concentration of chloride ions in the pit is continuously increased, and the corrosion is intensified.
In this case, the boiler feed water is not dechlorinated (in fact, it is not generally treated). The pot water contains a certain amount of chloride ions. If the boiler does not discharge normally enough, it will cause the concentration of chloride ions in the pot water. Increase, that is, the concentration of chloride ions. It can be judged that chlorine corrosion is also one of the causes of leakage and perforation of the pipe.
4.3 Interaction of Oxygen Corrosion and Chlorine Corrosion When oxygen corrosion occurs, the participation of chloride ions greatly accelerates the corrosion rate due to the higher concentration of chloride ions, and increases as the concentration of chloride ions increases. The chemical composition of ions in water is different, and the corrosion rate of dissolved oxygen is also different. If the water contains C1-, C1-, it has the ability to damage the protective film, thus promoting corrosion. Internal corrosion under the action of oxygen is exacerbated by the presence of chloride and sulfate in the water. When they form loose scale on the steel surface, the passivation film is destroyed and the development of local damage is accelerated.
Due to the operation and other reasons, the pot water contains a relatively high concentration of oxygen, chlorine and other ions, causing a combination of oxygen corrosion and chlorine corrosion, resulting in tube leakage and perforation of the boiler.
4.4 Condensate reuse The condensate of the steam boiler is almost pure water, and the temperature is mostly 60-70 ° C, and the reuse value is very high. For example, the reuse price of water alone will be around 10 yuan / ton, and considering the different fuel forms, condensate recovery temperature and other factors, the reuse value of condensed water may be as high as 18 to 25 yuan / ton. Therefore, the recovery of condensed water is in line with the general direction of “energy saving and consumption reductionâ€, and it can also enable enterprises to further save costs and obtain certain economic benefits.
However, in the process of recycling, there is a problem that cannot be ignored----the quality of condensate. The quality of the condensate is the key to the condensate recovery and reuse.
In low-pressure boilers, it is often found that the color of the recovered condensate is red or even soy sauce. This case is typical. This is because when the temperature increases, the HCO3- in the water is decomposed into CO2, and the CO2 gas condenses with the water vapor in the condensing recovery pipe, causing the pH of the return water to drop, and the condensed water is acidic. At the same time, the steam system and the condensate water pipe system enter due to air, and the CO2 in the air dissolves, and the pH value of the return water is also lowered. The corrosive nature of acidic water to pipelines and water tanks is an important factor in the excessive iron ions in the return water. Even if it is replaced by stainless steel pipes and stainless steel water tanks, it is impossible to change the acidity of the condensed return water quality, thus resulting in the quality of the collected condensate. It is not good enough to be reused directly. If it is used hard, it is a matter of time to cause chemical corrosion in the furnace.
4.5 Burner Reform From the perspective of environmental protection and energy saving, gas is definitely a high-quality, high-efficiency, clean and economical fuel for boilers. Therefore, a large number of single-fuel boilers have begun to transition to gas reform.
However, various modifications have focused on replacing burners and corresponding piping and controllers, and only on the basis of existing fuel-fired boilers, the fuel system has been improved (for example, switching to gas or oil/gas combustion). , adding gas pressure regulating valve, solenoid valve, leak detection device and gas filtration equipment), but the boiler body is not modified, it is considered "universal", but it is precisely this "universal" concept has caused future operation Imperfect.
When fuel is used, in the normal working condition of fuel and air ratio, fine oil droplet particles formed by fuel atomization enter the furnace, and these oil droplet particles quickly lose their initial velocity, and flow together with the airflow in the furnace, the furnace The space burns some solid carbon black and flammable gases. When gas fuel is burned in the furnace space, there is no gasification of volatile gas and solid carbon particles in the fuel gas. That is to say, the flame blackness of the two types of fuels is different when burned. Therefore, the radiation abilities of the flue gas generated by the combustion of these two types of fuels are different, and the final result of the formation is that the difference between the flue gas temperature at the exit of the furnace and the heat absorbed by the furnace is very different. In the case of a real general-purpose boiler design, the gas service conditions should be mainly used to check the fuel condition. However, the original purchase of this case is only imported single-fired boilers, and then changed to gas at the domestic site. From the operational observation point of view, in the case of gas, it seems that the heating area of ​​the furnace is obviously too small, resulting in an increase in the temperature of the furnace exit, "inlet effect" The working conditions of the rear tube sheet and the nozzle are deteriorated, and the evaporation strength zui here is large, and the heat load zui is high.
4.6 The structure of the boiler is welded for the pipe and the tube sheet. There is a large welding stress at this place. Usually, the corrosion will be more serious at the stress concentration. If the pre-extension is not taken before the welding, the gap is not reached, and the ring is partially formed. Water film, other boilers start and stop frequently, pressure fluctuations, will also promote and aggravate the negative effects of temperature alternating stress.
5 Handling and preventive measures 5.1 In strict accordance with the repair plan approved by the boiler safety supervision department, construction, inspection, inspection, flaw detection and hydraulic test shall be carried out in accordance with national standards.
5.2 In order to reduce the inlet effect at the tube sheet, in the current situation where the boiler structure cannot be changed, the operation adjustment of the gas burner should be strengthened, the length and diameter of the burner flame should be suppressed as necessary, and the excess air volume should be strictly controlled. A thin refractory layer may be applied to the surface of the tubesheet as appropriate.
5.3 Strengthening the national special equipment safety supervision department of water supply and deoxygenation to pay more and more attention to the harmfulness of boiler oxygen corrosion, and re-promulgated GB1576-2001 "Industrial Boiler Water Quality" in 2001. The standard clearly stipulates that for steam boilers, when the rated evaporation is greater than or When it is equal to 6t/h, oxygen should be removed. When it is less than 6t/h, if local corrosion is found, oxygen removal measures should be taken.
There are many ways to remove water from boiler feed water. For many years, we have been searching for a highly efficient, economical and stable oxygen removal method. However, this must be combined with the furnace type and the actual situation. In this case, the technical conditions of the boiler when ordering are clear. 104 ° C, now using chemical deaeration, the inlet water temperature is only 70 ° C, has been clearly out of the design operating conditions, whether the Zui for the economy is worthy of further discussion.
Even if chemical deaeration is used, it is necessary to arrange the necessary online or portable analytical instruments or equipment immediately to ensure that the situation is grasped in real time, and the concentration of the dosing agent is adjusted actively and in time to ensure the oxygen removal effect.
Deoxidizers must purchase regular packaging products from genuine companies and refuse bulk cargo. Chemical oxygen scavengers are preferred for US or German branded products.
5.4 Careful reuse of steam condensate The commonly used condensate treatment technology is the chemical method, which forms a membrane in the return line or increases the pH of the return water by adding a membrane amine and volatile ammonia at the steam outlet or furnace. To prevent the occurrence of corrosion and reach the standard of reuse. However, this method is only suitable for a heat exchange system with a single steam use and a short pipeline. For complex working conditions of steam, it often fails to achieve the desired treatment effect. There are many reasons for this, and there are problems with the system itself, and specific processes. Therefore, the use of chemicals to improve the corrosion of the backwater system is limited. If the investment is to be retrofitted, it is not realistic to increase the iron removal and hardening facilities. The only way to do this is to carefully consider the reuse of steam condensate. This should be chosen from the importance of the relationship between safety and economy.
5.5 Control the pH value of pot water in a reasonable range according to GB1576-2001 "Industrial Boiler Water Quality", pot water PH = 10 ~ 12, because in this range not only can prevent scale, but also anti-corrosion, but the premise is that the water is carried out Fully deoxidize.
Judging from the current operation of the boiler in this case, the deoxidation effect of the feed water is not ideal. In this case, it must be adjusted according to the actual situation. When the pot water is at a high temperature, when the pH is <8 or PH>13, the protective film on the metal surface of the boiler will be destroyed by dissolved oxygen, which will intensify the corrosion of the metal. When 7≤PH<10, the oxygen mainly occurs. The depolarization and ferrous hydroxide are oxidized, but they are very weak. When PH≥10, the corrosion of the steel is changed from homogeneous to local, and it has the conditions of ulcer and pitting, from most studies. The result is: if the boiler feed water is not deoxygenated or the oxygen removal is not complete, the pH value of the pot water is controlled to about 8-10, which can effectively prevent oxygen corrosion.
5.6 Strict operation of disciplined personnel The furnace personnel must strictly implement the operating procedures and process disciplines of various boilers and boiler rooms. Special emphasis should be placed on the following points: speed when loading the boiler, avoiding rapid boosting; daily strengthening of supervision of various water quality, conscientiously doing dosing and cleaning work; ensuring normal operation of the water softener, normal regeneration, and ensuring water treatment operation Correctness, prevent excessive chloride ions from entering the boiler; ensure the frequency and displacement of the boiler's regular discharge, ensure that the salt content of the boiler water is within normal standards, especially after the chemical dosing method is adopted, the importance of sewage discharge More obvious, the work must not be relaxed.
2Overview of an imported horizontal internal combustion pyrotechnics fuel-fired boiler with a rated evaporation of 6t/h, rated pressure 1.0Mpa, operating pressure 0.78Mpa, commissioned in June 1997, intermittent operation (accumulated nearly 4 years).
During the routine inspection in May 2008, it was found that there was dripping mark on the lower part of the smoke box behind the furnace, and it was required to stop the operation immediately. After the furnace was cooled, the smoke box was opened, and there was a phenomenon of water seepage in the lower part of the tube plate, and the pot water was drained. On the day of internal inspection, it was found that the pipe was corroded and perforated, and the specific position was the second return inlet from the top to the bottom of the row, from the left to the second, and the water side of the second return pipe was found to be close to the flashback. There is ulcerative oxygen corrosion at the chamber end.
3 Inspection and analysis 3.1 Macroscopic inspection The perforation of the pipe is located near the weld joint between the pipe and the tube sheet. There is a gray-brown corrosion product at the perforated part. After the corrosion product is scraped, it is corroded, and the depth is 2.9mm. The cross-section sample tube was cut by the nearby cutting. It was found that the corrosion of the corrosion pit originated from the outer wall of the pipe and was located beside the weld. The thickness of the bottom of the corrosion pit was obviously thinned, and the thin part of the zui had penetrated.
After the smoke pipe is taken out at the site, it can be seen that except for the perforated part of the pipe, the outer surface of other parts is also obviously scattered with a plurality of pits, and the pit has a layered covering, which is suspected of corrosion products.
Due to the limitation of the means, further chemical composition analysis and metallographic analysis of the extracted pipe section have not yet been carried out. However, since the boiler has been in normal operation for 10 years, it is preliminarily determined that the metallographic structure of the raw material of the pipe is normal, the chemical and mechanical properties are normal, and indirectly Exclude material reasons.
3.2 Data investigation On-site inspection of the product quality certification document of the boiler, found that the boiler product has a complete material certificate and inspection certificate, complete documentation, smoke pipe use in accordance with German TRD201St37.8, specifications φ63.5 × 2.9mm, equivalent In domestic 20# boiler tube (GB3087).
3.3 Operational investigation 3.3.1 The purpose of the steam boiler is to provide daily air consumption in the hotel laundry, heat exchangers for daily hot water through the heat exchanger, and heat source for the winter air conditioning system.
Due to the provision of a backup furnace, the boiler is not operated at full load for a long time. The annual operating state is intermittent use. The total operating period is about 4 months per year. The steam pressure during the operation is maintained at 0.68~0.78Mpa.
3.3.2 The furnace is supplied with water from the building pool. The raw water is municipal water supply. In order to ensure the sanitary standard of the water quality of the pool, the property personnel put the slow-release chlorine balls purchased from the health and epidemic prevention station into the pool, but the residual chlorine in the water was not monitored.
The furnace is equipped with the original US sodium ion exchanger, and it runs normally. The water is tested at the soft water outlet point of the exchanger, and the result is qualified.
The furnace is equipped with a thermal deaerator. For various reasons, the thermal deaerator is in intermittent operation. In 2005, the thermal deaeration was stopped and the chemical deaeration was changed, but the concentration of the dosing was constant all the year and the deionized water quality test was not carried out. .
The boiler reuses the condensate from the steam system. The soft water effluent enters a steel open water tank, and the condensed return water also directly enters the water tank. After the two are simply mixed, the water tank directly supplies water to the boiler. The current feed water temperature averages 40 to 50 ° C, and the Zui height can reach 70 ° C. .
3.3.3 Due to the civil construction of the boiler house, the installation of the sewage discharge expansion vessel and the corresponding pipeline is not perfect, and the regular sewage discharge during the daily operation of the boiler is not complete.
3.3.4 In the summer of 2006, the fuel system was reformed from single fuel to oil/gas. It has been in gas service for nearly one year.
4 Corrosion mechanism and cause analysis Corrosion refers to the damage of metal surface caused by chemical or electrochemical action under the action of surrounding medium. Corrosion damage can be either monolithic or local, and it can be uniform or non-uniform. From the morphology and analysis of the corrosion of the boiler pipe, it can be concluded that the corrosion of the pipe is a local uneven electrochemical corrosion. Specifically, the reason for the corrosion of the pipe is as follows.
4.1 Oxygen corrosion and its causes For boiler pressure components, the water side is mainly electrochemical corrosion, and the fire side (or smoke side) is mainly chemical corrosion. Oxygen corrosion is electrochemical corrosion, mainly due to dissolved oxygen in water. At normal temperature, the dissolved oxygen concentration in water is about 9.1mg / L (1 absolute atmospheric pressure, 20 ° C), while GB1576-2001 "industrial boiler water quality" requires rated steam pressure ≤ 1.0MPa, dissolved oxygen concentration ≤ 0.1mg / L, too High is likely to cause metal corrosion. The mechanism is that iron and oxygen form two electrodes, which constitute an etching battery. In the corrosion battery, the potential of iron is always lower than the electrode potential of oxygen, so iron is the anode of the battery, and the pot water is a polar electrolyte in water. Under the attraction of the polar molecules, a part of the iron atoms on the surface of the steel began to move into the pot water to become positively charged iron ions, while the excess electrons on the steel were negatively charged. If iron ions continue to enter the pot water, pits are gradually formed on the steel sheet (tube), causing corrosion.
Dissolved oxygen in the pot water has a depolarizing effect that exacerbates this process. The strength of depolarization is related to the amount of oxygen, that is to say, the amount of dissolved oxygen determines the strength of corrosion, and the two are linearly proportional. The main factor affecting oxygen corrosion is the concentration of dissolved oxygen in water. Dissolved Oxygen Corrosion As the amount of dissolved oxygen in the water increases and the water temperature increases, the corrosivity becomes stronger.
The boiler has an evaporation capacity of 6t/h. Although chemical deaeration is now used, there is no means to measure the oxygen content, which results in incomplete dehydration of the feed water. Therefore, the pot water must contain a certain concentration of oxygen, and oxygen corrosion is formed after the operation. The macroscopic feature of oxygen corrosion is the formation of ulcerated rust on the surface of the metal. The surface of the ulcer rust is a yellow-brown or brick-red hard shell, and the lower layer is a black powder. After the powder is removed, it will appear as a pit. In this case, the obvious ulcer rust on the perforation of the pipe, the corrosion on the metal surface will locally expand to the depth, and the perforation is gradually formed. It can be confirmed that oxygen corrosion is an important cause of leakage and perforation of the pipe.
4.2 Chlorine Corrosion and Its Causes Chloride ion exchange has a high corrosion rate to metals due to its small chloride ion radius and its typical activated anion, which is more active in the presence of dissolved oxygen. With the operation of the boiler, if the salt content of the pot water increases, the chloride ion concentration increases continuously, and more chloride deposits appear in the bottom of the boiler, the pipe and the water circulation are weak. When oxygen corrosion occurs, the metal is continuously dissolved, and the metal cations in the corrosion pit are continuously increased. In order to maintain the charge balance, the chloride ions in the water continuously migrate into the corrosion pit, so that the concentration of chloride ions in the pit is continuously increased, and the corrosion is intensified.
In this case, the boiler feed water is not dechlorinated (in fact, it is not generally treated). The pot water contains a certain amount of chloride ions. If the boiler does not discharge normally enough, it will cause the concentration of chloride ions in the pot water. Increase, that is, the concentration of chloride ions. It can be judged that chlorine corrosion is also one of the causes of leakage and perforation of the pipe.
4.3 Interaction of Oxygen Corrosion and Chlorine Corrosion When oxygen corrosion occurs, the participation of chloride ions greatly accelerates the corrosion rate due to the higher concentration of chloride ions, and increases as the concentration of chloride ions increases. The chemical composition of ions in water is different, and the corrosion rate of dissolved oxygen is also different. If the water contains C1-, C1-, it has the ability to damage the protective film, thus promoting corrosion. Internal corrosion under the action of oxygen is exacerbated by the presence of chloride and sulfate in the water. When they form loose scale on the steel surface, the passivation film is destroyed and the development of local damage is accelerated.
Due to the operation and other reasons, the pot water contains a relatively high concentration of oxygen, chlorine and other ions, causing a combination of oxygen corrosion and chlorine corrosion, resulting in tube leakage and perforation of the boiler.
4.4 Condensate reuse The condensate of the steam boiler is almost pure water, and the temperature is mostly 60-70 ° C, and the reuse value is very high. For example, the reuse price of water alone will be around 10 yuan / ton, and considering the different fuel forms, condensate recovery temperature and other factors, the reuse value of condensed water may be as high as 18 to 25 yuan / ton. Therefore, the recovery of condensed water is in line with the general direction of “energy saving and consumption reductionâ€, and it can also enable enterprises to further save costs and obtain certain economic benefits.
However, in the process of recycling, there is a problem that cannot be ignored----the quality of condensate. The quality of the condensate is the key to the condensate recovery and reuse.
In low-pressure boilers, it is often found that the color of the recovered condensate is red or even soy sauce. This case is typical. This is because when the temperature increases, the HCO3- in the water is decomposed into CO2, and the CO2 gas condenses with the water vapor in the condensing recovery pipe, causing the pH of the return water to drop, and the condensed water is acidic. At the same time, the steam system and the condensate water pipe system enter due to air, and the CO2 in the air dissolves, and the pH value of the return water is also lowered. The corrosive nature of acidic water to pipelines and water tanks is an important factor in the excessive iron ions in the return water. Even if it is replaced by stainless steel pipes and stainless steel water tanks, it is impossible to change the acidity of the condensed return water quality, thus resulting in the quality of the collected condensate. It is not good enough to be reused directly. If it is used hard, it is a matter of time to cause chemical corrosion in the furnace.
4.5 Burner Reform From the perspective of environmental protection and energy saving, gas is definitely a high-quality, high-efficiency, clean and economical fuel for boilers. Therefore, a large number of single-fuel boilers have begun to transition to gas reform.
However, various modifications have focused on replacing burners and corresponding piping and controllers, and only on the basis of existing fuel-fired boilers, the fuel system has been improved (for example, switching to gas or oil/gas combustion). , adding gas pressure regulating valve, solenoid valve, leak detection device and gas filtration equipment), but the boiler body is not modified, it is considered "universal", but it is precisely this "universal" concept has caused future operation Imperfect.
When fuel is used, in the normal working condition of fuel and air ratio, fine oil droplet particles formed by fuel atomization enter the furnace, and these oil droplet particles quickly lose their initial velocity, and flow together with the airflow in the furnace, the furnace The space burns some solid carbon black and flammable gases. When gas fuel is burned in the furnace space, there is no gasification of volatile gas and solid carbon particles in the fuel gas. That is to say, the flame blackness of the two types of fuels is different when burned. Therefore, the radiation abilities of the flue gas generated by the combustion of these two types of fuels are different, and the final result of the formation is that the difference between the flue gas temperature at the exit of the furnace and the heat absorbed by the furnace is very different. In the case of a real general-purpose boiler design, the gas service conditions should be mainly used to check the fuel condition. However, the original purchase of this case is only imported single-fired boilers, and then changed to gas at the domestic site. From the operational observation point of view, in the case of gas, it seems that the heating area of ​​the furnace is obviously too small, resulting in an increase in the temperature of the furnace exit, "inlet effect" The working conditions of the rear tube sheet and the nozzle are deteriorated, and the evaporation strength zui here is large, and the heat load zui is high.
4.6 The structure of the boiler is welded for the pipe and the tube sheet. There is a large welding stress at this place. Usually, the corrosion will be more serious at the stress concentration. If the pre-extension is not taken before the welding, the gap is not reached, and the ring is partially formed. Water film, other boilers start and stop frequently, pressure fluctuations, will also promote and aggravate the negative effects of temperature alternating stress.
5 Handling and preventive measures 5.1 In strict accordance with the repair plan approved by the boiler safety supervision department, construction, inspection, inspection, flaw detection and hydraulic test shall be carried out in accordance with national standards.
5.2 In order to reduce the inlet effect at the tube sheet, in the current situation where the boiler structure cannot be changed, the operation adjustment of the gas burner should be strengthened, the length and diameter of the burner flame should be suppressed as necessary, and the excess air volume should be strictly controlled. A thin refractory layer may be applied to the surface of the tubesheet as appropriate.
5.3 Strengthening the national special equipment safety supervision department of water supply and deoxygenation to pay more and more attention to the harmfulness of boiler oxygen corrosion, and re-promulgated GB1576-2001 "Industrial Boiler Water Quality" in 2001. The standard clearly stipulates that for steam boilers, when the rated evaporation is greater than or When it is equal to 6t/h, oxygen should be removed. When it is less than 6t/h, if local corrosion is found, oxygen removal measures should be taken.
There are many ways to remove water from boiler feed water. For many years, we have been searching for a highly efficient, economical and stable oxygen removal method. However, this must be combined with the furnace type and the actual situation. In this case, the technical conditions of the boiler when ordering are clear. 104 ° C, now using chemical deaeration, the inlet water temperature is only 70 ° C, has been clearly out of the design operating conditions, whether the Zui for the economy is worthy of further discussion.
Even if chemical deaeration is used, it is necessary to arrange the necessary online or portable analytical instruments or equipment immediately to ensure that the situation is grasped in real time, and the concentration of the dosing agent is adjusted actively and in time to ensure the oxygen removal effect.
Deoxidizers must purchase regular packaging products from genuine companies and refuse bulk cargo. Chemical oxygen scavengers are preferred for US or German branded products.
5.4 Careful reuse of steam condensate The commonly used condensate treatment technology is the chemical method, which forms a membrane in the return line or increases the pH of the return water by adding a membrane amine and volatile ammonia at the steam outlet or furnace. To prevent the occurrence of corrosion and reach the standard of reuse. However, this method is only suitable for a heat exchange system with a single steam use and a short pipeline. For complex working conditions of steam, it often fails to achieve the desired treatment effect. There are many reasons for this, and there are problems with the system itself, and specific processes. Therefore, the use of chemicals to improve the corrosion of the backwater system is limited. If the investment is to be retrofitted, it is not realistic to increase the iron removal and hardening facilities. The only way to do this is to carefully consider the reuse of steam condensate. This should be chosen from the importance of the relationship between safety and economy.
5.5 Control the pH value of pot water in a reasonable range according to GB1576-2001 "Industrial Boiler Water Quality", pot water PH = 10 ~ 12, because in this range not only can prevent scale, but also anti-corrosion, but the premise is that the water is carried out Fully deoxidize.
Judging from the current operation of the boiler in this case, the deoxidation effect of the feed water is not ideal. In this case, it must be adjusted according to the actual situation. When the pot water is at a high temperature, when the pH is <8 or PH>13, the protective film on the metal surface of the boiler will be destroyed by dissolved oxygen, which will intensify the corrosion of the metal. When 7≤PH<10, the oxygen mainly occurs. The depolarization and ferrous hydroxide are oxidized, but they are very weak. When PH≥10, the corrosion of the steel is changed from homogeneous to local, and it has the conditions of ulcer and pitting, from most studies. The result is: if the boiler feed water is not deoxygenated or the oxygen removal is not complete, the pH value of the pot water is controlled to about 8-10, which can effectively prevent oxygen corrosion.
5.6 Strict operation of disciplined personnel The furnace personnel must strictly implement the operating procedures and process disciplines of various boilers and boiler rooms. Special emphasis should be placed on the following points: speed when loading the boiler, avoiding rapid boosting; daily strengthening of supervision of various water quality, conscientiously doing dosing and cleaning work; ensuring normal operation of the water softener, normal regeneration, and ensuring water treatment operation Correctness, prevent excessive chloride ions from entering the boiler; ensure the frequency and displacement of the boiler's regular discharge, ensure that the salt content of the boiler water is within normal standards, especially after the chemical dosing method is adopted, the importance of sewage discharge More obvious, the work must not be relaxed.
Pain Relief Patch For Neck Shoulder,Lower Back And Leg
Pain Relief Patch for neck shoulder, lower back and leg.
[Name] Medical Cold Patch
[Package Dimension] 10cm×12cm 2pieces/box
The pain relief patch is composed of three layers, namely, backing lining, middle gel and protective film. It is free from pharmacological, immunological or metabolic ingredients.
[Scope of Application] For cold physiotherapy, closed soft tissue only.
[Indications]
The patches give fast acting pain relief for strains, sprains, cramp, bruises, swollen areas or joint stiffness.
[How To Use a Patch]
Tear off the packaging bag and remove the patch. Remove the protective film and apply the patch on the skin. One piece, one time. The curing effect of each piece can last for 8-12 hours.
[Attention]
Do not apply the patch on the problematic skin, such as wounds, eczema, dermatitis,or in the eyes. People allergic to herbs and the pregnant are advised not to use the medication. If swelling or irritation occurs, please stop using and if any of these effects persist or worsen.notify your doctor or pharmacist promptly. Children using the patch must be supervised by adults.
[Storage Conditions]
Store below 30c in a dry place away from heat and direct sunlight.
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