Burners maintenance

The advantages of thermal incineration are that it is simple in concept, has a wide application, and results in almost complete destruction of pollutants with no liquid or solid residue. Thermal incineration provides an opportunity for heat recovery and has low maintenance requirements and low capital cost. Thermal incineration units for small or moderate exhaust streams are generally compact and light. Such units can be installed on a roof when the plant area is limited. = The main disadvantage is the auxiliary fuel cost, which is partly offset with an efficient heat-recovery system. The formation of nitric oxides during the combustion processes must be reduced by control of excess air temperature, fuel supply, and combustion air distribution at the burner inlet, The formation of thermal NO increases dramatically above 980 Table 13.10)... 

The steam flow was (3.55 ton/hr, but the nitrogen flow was only 0.4 ton/hr, the most that could be made available. As the system cooled, air was drawn in. Some liquid hydrocarbon had been left in a blowdown vessel, and the air and hydrocarbon vapor formed a flammable mixture. According to the report, this moved up the stack and was ignited by the pilot burner, which was still lit. It is possible, however, that it was ignited by the maintenance operations. 

Velocity flame stoppers have been used for feeding waste fuel gas to furnace burners when the gas can become flammable due to contamination with air. They have also been used for feeding waste or depleted air streams to furnaces when the air streams can become contaminated with flammable gases (Howard 1982). It should be noted that a furnace pressure transient may render this device ineffective and consideration should be given to providing an upstream detonation flame arrester. In this arrangement a demand will only be placed on the detonation flame arrester when the velocity flame stopper fails. Therefore, detonation flame arrester maintenance should be minimal. 

Combustion equipment can be set to give optimum efficiency at the time of commissioning but this condition will not be maintained. Wear and tear on control valves, partial blockage of filters, sooting of surfaces, etc. will all cause a fall in efficiency. To counter this, regular maintenance is desirable, and must include routine flue analysis and burner adjustment. 

Most combustion equipment is not controlled by means of a feedback from flue gas analysis but is preset at the time of commissioning and preferably checked and reset at intervals as part of a planned maintenance schedule. It is difficult to set the burner for optimum efficiency at all firing rates and some compromise is necessary, depending on the control valves used and the control mode (e.g. on/off, fully modulating, etc.). 

After any maintenance work involving replacement or adjustment of components it is essential that the plant be re-commissioned in a safe way, including dry mns with the gas turned off to ensure that flame failure devices operate correctly and pilot turndown tests to ensure that if the pilot can energize the flame detector then it can also smoothly ignite the main burner. 

Characteristics of various atomizers are given in Table 24.1. Primary considerations are selecting the best principle for the type of fuel, the size of the burner/boiler and the type of application. Other important characteristics are ability to operate with the minimum of excess air, turndown ratio and questions of durability and maintenance. 

Electric boilers are generally inherently simpler to own and operate because there is no combustion system required (fuel tanks, pumps, burners, regulators, flame safeguards, etc.). Also space requirements are smaller and capital and maintenance costs often are lower. In addition, electric boilers typically do not require full-time operators. 

Characterized by high efficiency and heating rate, (2) Deployment of well-designed, durable and neatly made burners ensures smokeless combustion, (3) Needs little care for maintenance purpose, (4) Easy control and flexibility, (5) Easy manipulation,... 

Finally, periodic cleaning of the burner head and nebulizer is needed to ensure minimal noise level due to impurities in the flame. Scraping the slot in the burner head with a sharp knife or razor blade to remove carbon deposits and removing the burner head for the purpose of cleaning it in an ultrasonic cleaner bath are two commonplace maintenance chores. The nebulizer should be dismantled, inspected, and cleaned periodically to remove impurities that may be collected there. 

Flue gas recirculation Flue gas recirculation, alone or in combination with other modifications, can significantly reduce thermal NO,. Recirculated flue gas is a diluent that reduces flame temperatures. External and internal recirculation paths have been applied internal recirculation can be accomplished by jet entrainment using either combustion air or fuel jet energy external recirculation requires a fan or a jet pump (driven by the combustion air). When combined with staged-air or staged-fuel methods, NO emissions from gas-fired burners can be reduced by 50 to 90 percent. In some applications, external flue-gas recirculation can decrease thermal efficiency. Condensation in the recirculation loop can cause operating problems and increase maintenance requirements. 

Carbon monoxide sensor. Carbon monoxide is a toxic air pollutant originating from incomplete combustion of fuels in burners or engines. Despite a strong demand for a very reliable carbon monoxide sensor, the only available sensor was based on an electrochemical type until recently. In this type sensor, selectivity and sensitivity for CO can often be enhanced by selecting elecrode materials and electrode potential appropriately, but several disadvantages are encountered, such as, short life, difficult maintenance and a rather expensive price. 

Features, such as the inclusion of a prereformer, installation of a ring-type burner with nozzles for the secondary reformer and upgrading to an S-300 ammonia converter, are all features that can be applied for existing ammonia plants. These features will ease maintenance and improve plant efficiency. 

As the plenum chamber is approximately at atmospheric pressure, the burners are still natural draft burners. To control the air shutters, each burner has a lever which can be controlled from the outside. The additional mounted side-wall plates consist of different segments to ensure good maintenance. 

For smaller furnaces, a single slag door burner is convenient and adequate since the operator can effectively reach all cold spots by aiming the burner as necessary. For larger furnaces, generally three sidewall-mounted burners are optimal (Table 5.1). If a foamy slag practice is employed, roof-mounted burners can reduce maintenance requirements. However, in many cases, roof mounting has led to considerable installation and maintenance costs. 

Standard burners that were designed more for fuel economy and maintenance ease than for NO, control. 

Table 1.4 lists the priority R D needs that were identified for burners, boilers, and furnaces. Essentially all of these needs require some amount of testing. These needs were generated from the following end-use requirements increased system efficiency reduced NOx, CO, CO2, and particulate emissions increased fuel flexibility more robust and flexible process control and operations better safety, reliability, and maintenance lower capital and operational costs faster, low-cost technology development and enhanced system integration. Coupled with these needs are some barriers to improvement financial risk, inability to accurately predict the performance of new systems, lack of industry standards, and the wide gap that often exists between the research done at a small scale that needs to be applied to industrial-scale systems. Testing is often required to address some of these barriers. 

There are two primary shapes for fhe ouflef nozzle of industrial burners round or rectangular. Figure 1.41 shows identical heaters with the same number of burners, but with different burner shapes round flame and flat flame. Round flames are fhe predominant shape used in industry. Most of the burners discussed in this book are predominantly round. This is often due to the lower cost of making round shapes compared to making rectangular shapes. It is also often due to the burner tile where round shapes generally require less maintenance... 

Portable systems allow a maintenance engineer to serve multiple boilers or burners. Tyqiically used for tuning... 

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