Inlet Flue Gas Temperature Research Articles

STUDY OF MIXED-CONVECTION HEAT TRANSFER FROM AN IMPINGING JET TO A SOLID WALL USING A FINITE-ELEMENT METHOD—APPLICATION TO COOKTOP MODELING

The mixed-convection flow from a hot vertical impinging jet on a colder horizontal disc has been studied. The geometry is analogous to a conventional burning gas cooktop. A numerical simulation of the system has been carried out using the finite-element method to study the dependence of fluid flow and heat transfer on the geometric, thermal, and fluid flow parameters. Results show that heat transfer efficiency versus several parameters such as inlet velocity magnitude and flue gas temperature has an optimum value, in which heat transfer efficiency is maximum. With thermal conductivity of the solid wall, velocity angle, and solid wall diameter heat transfer efficiency has increasing behavior. Finally, with solid wall height and solid wall thickness, heat transfer efficiency has diminishing behavior.

An Experimental Approach to Evaluate the Desulfurization Yield in Spray Drying Sorber

A pilot-scale Spray Drying Sorber (SDS) system was set up to evaluate the effect of spray characteristics on the desulfurization yield. The size distribution and the Sauter Mean Diameters of slurry droplets were measured in advance using the optical size measurement system, Malvern 2600. The desulfurization yield of the drying chamber by size was measured for the conditions of inlet gas and spray injection. As a reagent, 10% limestone slurry of was treated with flue gas containing , and the combustion gas analyzer and gas detectors were attached to measure the concentration. With a flow rate of 144 Nm3/h and a temperature range of , the experiments were performed for the Stoichiometric Ratio (SR) of 1.0 to 3.0 and droplet mean diameter of 6.5 to . In case of smaller spray droplets, the desulfurization efficiency improved due to the increase of total droplet surface area, while the reduction in evaporation time reduced the contact time between the droplets and gas. In some typical region of droplet diameter, this negative effect, reduction of contact time, became dominant and the desulfurization yield decreases the desulfurization yield in spite of the expansion in absorption area. These results revealed that there exists the optimal size of spray droplets for a given state, which is determined by the compromise between the total surface area of slurry droplets and the evaporation time of droplets. The measurements also indicated that the inlet temperature of flue gas changes the optimal injection condition by varying the driving force for evaporation. The results confirm that the effect of the evaporation time of slurry droplets should be considered in analyzing the desulfurization yield as well as the total surface area, for it is a significant aspect of the correlation with the capabilities of absorption in wet droplets. In conclusion, the optimal condition of spray can be determined based on these results, which might be applied to design or scale-up of SDS system.

Predicting Removal of Coal Ash Deposits in Convective Heat Exchangers

Electric utilities are under pressure to reduce emissions and increase efficiency, and this means that coal-fired power plants must meet new challenges such as switching to coals for which the units were not designed. Ash deposition in coal-fired power plants reduces heat transfer and can cause the plant to be shut down. Ash deposits on convective heat transfer surfaces are generally removed mechanically by soot-blowers. On-line cleaning is practical as long as the ash deposits are not highly sintered. The sintering behavior of deposits is complex and depends on flue gas temperature, ash particle size, and ash composition. In this paper, a method is presented for estimating, for a specific coal, the maximum flue gas inlet temperature that allows the convective heat exchanger to be cleaned using conventional means. The calculation was carried out for conditions that represent the steam superheater section of a conventional pulverized coal-fired power plant, and the results are consistent with observations from existing plants. The method was then applied to the design of a novel air heater being designed for the Combustion 2000 HIPPS program.

A vacuum technic for the chemist

A Transport Membrane Condenser (TMC), made from nanoporous membrane tube bundles, was developed to recover the water vapor and its significant amount of latent heat from boiler flue gases to improve boiler efficiency and save water. Experiments have been carried out to study the phenomena for both a nanoporous membrane tube bundle and an impermeable stainless steel tube bundle with the same characteristic dimensions. Flue gas streams with water vapor mass fraction 11.3%, temperature range from 65 °C to 95 °C are used for the experimental study, which covers the typical TMC waste heat recovery application parameter ranges. Results show convection Nusselt numbers of the membrane tube bundle are 50–80% higher than that of the impermeable stainless steel tube bundle at typical condensation heat transfer conditions. The parametric study has been done by varying cooling water inlet flow rate, water inlet temperature, flue gas inlet flow rate, inlet temperature, and inlet dew point. The condensing heat transfer enhancement effect gives a good perspective for using nanoporous membrane surface to design high efficiency condensing heat exchangers to recover both water vapor and its latent heat from high moisture content low grade waste heat streams.