Recuperative system

Electronic ratio controller. In this type of controller, a proportion of both gas and air is diverted through a bypass in which a thermistor sensor measures the flow. The air and gas flows can be compared and the ratio calculated and displayed. A ratio control valve in the air or gas supply, depending on whether the mode of operation is gas- or air-led, will automatically restore a deviation from the pre-set ratio. The electronic controller maintains ratio over a 19 1 turndown. The principle of operation is based on mass flow, so that it can be used with preheated air in recuperative systems. 

It has to be noticed that although the profiles have been compared for the same maximum reference point temperature, the maximum temperature on the profiles, created for the right side of the tube, is not the same. It is due to the location of the TRP on the top of the tube. The real obtained maximum temperatures of the reference point are shown on graphs in Figure 24.13 and in Table 24.2. For all tests, the TRP point is situated on or very close to profile in the case of the HRS, while for the recuperative system this point usually is about 20°C higher than the maximum temperature of the right side profile. This is a result of nonuniform temperature distribution on the circumference, which will be explained further. 

The graphs also show that for a cross-sectional profile, the temperature differences around the cross section of the tube are lower in the case of the HRS. In the case of the recuperative system, there is a noticeable (around 25°C) temperature difference between the top and bottom sides of the tube. This difference is due to heating by the upper, hotter part and cooling by the lower, colder part of the tube. In the case of HRS, the temperature difference between both ends of the tube is negligible, because of cyclic work of the system and uniform, symmetrical, and longitudinal temperature profile. However, higher temperature at the bottom side, than that on the top, can be observed in contrast with the recuperative system. In this case it is because the considered measurement point is located closer to the lower part of the tube. This difference is negligible and in the result, the cross-sectional temperature profile is also more uniform. 

As a result, the profile in the case of HRS was moved down a few degrees to lower the temperature region and the profile in the case of recuperative system was... 

The measurement and calculation results (Table 24.4) clearly reveal that efficiency of the whole system is higher in the case of a HRS. The difference is significantly big, up to 25%. It becomes bigger in higher temperatures of the reference point. Higher efficiency for HRS is mainly due to a lower temperature of flue gases. The surface losses are also lower, because of a smaller surface area of burner units and pipes in comparison with a recuperative system. 

The pollutant emission measurements show that a FLRS works with higher efficiency wifhouf fhe cosf of higher NO emission. For example NO emission from fhe conventional recuperative system, calculated for X=, was equal to 179 ppm and 284 ppm in test CRS-1 and CRS-2, respectively, while it was more or less the same using HRS, 167 ppm and 316 ppm for HRS-1 and HRS-2 fesfs, respectively. No emission of CO was observed during normal operation for both systems. 

The measurement of pressure difference across the systems revealed that the pressure drop due to HRS is more than 10 times higher than that when the conventional recuperative system is in operation. The pressure drop was 1.7 mbar and 2.8 mbar in cases CRS-3 and CRS-4, respectively, while it was 36 mbar and 30 mbar for HRS-3 and HRS-4, respectively. 

Rafidi, N, Blasiak, W., Jewartowski, M., and Szewczyk, D. "Increase of the Effective Energy from the Radiant Tube Equipped with Regenerative System in Comparison with Conventional Recuperative System." IFRF Combustion Journal, Article No 200503, ISSN 1562-479X, 2005. 

Recuperative systems offer increased energy and thermal efficiencies. The effect of air preheating on thermal efficiency and coke use is depicted in Figure 2.10. It should be noted that the coke quality may affect the overall blast efficiency. 

Regenerative heat exchange can be more expensive to install but can readily offer 95% heat recovery efficiency. Regenerative systems are therefore best suited to more dilute streams or those with variable VOC concentration they are widely used in coatings applications. Recuperative systems are more cost effective for higher-concentration VOC streams of constant composition they find widespread use in chemical production. Both recuperative and regenerative heat recovery can be used with either thermal or catalytic oxidation systems and with secondary heat recovery. 

Recuperative systems use conventional shell-and-tube or plate-type heat exchangers. Plate-type units are reported to be more economical for low to moderate temperature service (to about 1,000°F), while shell and tube are preferable for higher temperatures (van der Vaart et al., 1990). Because of the temperature limitations of conventional heat exchangers, recuperative systems are normally designed to heat the feed gas to no more than l,200°F. A conventional. shell-and-tube recuperative system can typically recover 60 to 80% of the available energy. 

Regenerative systems have appreciably higher capital costs than recuperative systems however, their lower fuel consumption makes them cost effective when large flows (greater than 10,(XK) cfm) and low solvent concentrations (less than about 10% of the lower explosive limit) are present (Renko, 1990). The regenerative systems have other potential advantages. They can operate at temperatures up to about 2,000°F, while recuperative systems are limit-... 

There are two types of heat exchangers Regenerative and Recuperative. The term regenerative heat exchanger is used for a system in which the... 

The results of the performance calculations are summarized in Table 9-24. The efficiency of the overall power system, work output divided by the lower heating value (LHV) of the CH4 fuel, is increased from 57% for the fuel cell alone to 82% for the overall system with a 30 F difference in the recuperative exchanger and to 76% for an 80 F difference. This regenerative Brayton cycle heat rejection and heat-fuel recovery arrangement is perhaps the simplest approach to heat recovery. It makes minimal demands on fuel cell heat removal and gas turbine arrangements, has minimal number of system components, and makes the most of the inherent high efficiency of the fuel cell. 

The effectiveness of the regenerative Brayton cycle performance will depend on the efficiency of the fuel cell, compressor, and turbine units the pressure loss of gases flowing through the system the approach temperatures reached in the recuperative exchanger and, most importantly, the cost of the overall system. 

Typical unit operations required for this system include vaporizers/preheaters, a pyrolysis reactor, and recuperative heat exchangers. One of the challenges with this approach is the potential for fouling by the carbon formed, which is particularly important in microreactors. 

The SRCO catalytic combustion unit treats volatile organic compound (VOC) laden process exhaust air. SRCO stands for self-recuperative catalytic oxidizer. The SRCO can be furnished as a complete operating vacuum extraction and catalytic oxidation system or as a stand-alone catalytic oxidizer to interface with an existing vacuum extraction and/or air stripper system. HD-SRCO stands for halogenated destruction self-recuperative catalytic oxidizer. This system is basically the same as the SRCO system, except that it remediates halogenated hydrocarbons using a different catalyst. 

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