外文翻译---燃煤锅炉的燃烧进程控制(编辑修改稿)

外文翻译---燃煤锅炉的燃烧进程控制(编辑修改稿)内容摘要：

nhearth, coke, and natural gases) flatflame burners in the boilers of cogeneration stations at metallurgical plants in Ukraine and Russia. Unfortunately, we have to state that, even at present, those in charge of selecting the type, quantity, and layout of burners in a furnace sometimes adopt technical solutions that are far from being optimal. This problem should therefore be considered in more detail. If we increase the number of burners nb in a furnace while retaining their total crosssectional area (ΣFb=idem) and the total flowrate of air through them, their equivalent diameters deq will bee smaller, as willthe jet momentums Gbwb, resulting in a corresponding decrease in the jet throw distance hb and the mass they eject. The space with high velocity gradients also bees smaller, resulting in poorer mixing in the furnace as a whole. This factor bees especially important when the emissions of NOx and CO are suppressed right inside the furnace using staged bustion (at αb 1) under the conditions of a fortiori nonuniform distribution of fuel among the burners. In [1], a quantitative relationship was established between the parameters characterizing the quality with which once through jets mix with one another as they flow into a limited space with the geometrical parameter of concentration = with nb = idem and Gb = idem. By decreasing this parameter we improve the mass transfer in the furnace。 however, this entails an increase in the flow velocity and the expenditure of energy (pressure drop) in the burners with the same Fb. At the same time, we know from experience and calculations that good mixing in a furnace can be obtained without increasing the head loss if we resort to large longrange jets. This allows a much less stringent requirement to be placed on the degree of uniformity with which fuel must be distributed among the burners. Moreover, fuel may in this case be fed to the furnace location where it is required from process control considerations. For illustration purposes, we will estimate the effect the number of burners has on the mixing in a furnace at = = idem. schematically shows the plan views of two furnace chambers differing in the number of once through round nozzles (two and four) placed in a tier (on one 大连交通大学 2020 届本科生毕业设计外文翻译 5 side of the furnace). The furnaces have the same total outlet crosssectional areas of the nozzles (ΣFb) and the same jet velocities related to these areas (wb). The wellknown swirl furnace of the TsKTI has a design close to the furnace arrangement under consideration. According to the data of [1], the air fraction βair that characterizes the mixing and enters through once through burners into the furnace volume beneath them can be estimated using the formula βair = 1 – (3) which has been verified in the range = – for a furnace chamber equipped with two frontal once through burners. Obviously, if we increase the number of burners by a factor of 2, their equivalent diameter, the length of the initial section of jets S0 and the area they ―serve‖ will reduce by a factor of Then, for example, at = , the fraction βair will decrease from to . Thus, Eq. (3) may be written in the following form for approximately assessing the effect of once through burners on the quality of mixing in a furnace:βair = 1 – nb 39。 ,where is the number of burners (or air nozzles) on one wall when they are arranged in one tier both in onesided and opposite manners. The number of burners may be tentatively related to the furnace depth a f (at the same = idem) using the expression (5) It should be noted that the axes of two large opposite air nozzles ( = 1)—an arrangement implemented in an inverted furnace—had to be inclined downward by more than 50176。 [8]. One wellknown example of a furnace device in which once through jets are used to create a large vortex covering a considerable part of its volume is a furnace with tangentially arranged burners. Such furnaces have received especially wide use in bination with pulverizing fans. However, burners with channels having a small equivalent diameter are frequently used for firing lowcalorific brown coals with high content of moisture. As a result, the jets of airdust mixture and secondary air that go out from their channels at different velocities(w2/w1 = 2–3) bee turbulized and lose the ability to be thrown a long distance。 as a consequence, the flame es closer to the waterwalls and the latter are contaminated with slag. One method by which the tangential bustion scheme can be improved consists of organizing the socalled concentric admission of large jets of airdust mixture and secondary air with the fuel and air nozzles spaced apart from one another over the furnace。