Method and apparatus for recuperative heating of reactants in an reaction matrix

#The present invention is directed to a method and apparatus for the controlled exothermic reaction, and, in particular, for the combustion, of gases or vapors within a bed matrix whereby the stability and movement of the reaction wave is controlled to minimize or eliminate undesirable emission products such as NO.sub.x and products of incomplete reaction such as CO and hydrocarbons, and wherein the gases or vapors may be heated prior to combustion by an efficient heat recuperation system. The present invention is also directed to a method and apparatus for heating a working fluid by passing the working fluid through pipes in thermal contact with the matrix of the aforementioned system.

#Many process streams of vapors, such as effluents from chemical processing plants, refineries, paint booth units, etc., utilize combustors to destroy the toxic or reactive constituents of the process gases or vapors prior to release to the atmosphere. Combustors are also utilized to generate energy through the oxidation of fuels such as methane. However, with increasing demands on environmental control of emissions, the use of free flames to combust such effluents is in many cases unsatisfactory. For example, standard combustors are particularly undesirable when dealing with chlorinated hydrocarbons.

#A free flame also results, in some instances, in incomplete combustion and uncontrollable production of undesirable side products. Because combustors typically operate at flame temperatures on the order of 3500.degree. F., significant amounts of unwanted NO.sub.x are often produced. Nitrous oxide (N.sub.2 O) and ammonia (NH.sub.3) are often by-products of NO.sub.x removal techniques.

#FIG. 1 plots heat transferred versus mass flow for four model heat-transfer systems.

#FIG. 2 plots frictional power loss versus mass flow for the four model heat-transfer systems.

#FIG. 3 plots the ratio of heat transferred to frictional power loss versus mass flow for the four model heat-transfer systems.

#The preferred apparatus according to the present invention contains a bed of heat-resistant material and means for monitoring the temperature along the flowpath of gases through the heat-resistant material. By monitoring the temperature of the resulting reaction wave within the bed matrix and controlling the flow and/or volume of gases entering and leaving the matrix as well as the temperature of the matrix, the reaction wave may be maintained at a relatively uniform temperature radially and at a constant location within the bed. The reaction matrix bed may be sized for any desired flow stream by altering the matrix flow cross-section, height, material, void fraction, outlet temperature, and supplemental heat or fuel value addition, if desired. Preferred matrix materials are ceramic balls, but other bed materials and configurations may be used, including, but not limited to, other random ceramic packings such as saddles or pall rings, structured ceramic packing, ceramic or metal foam, metal or ceramic wool and the like.

#By maintaining the stability and uniformity of temperature of the reaction wave within the matrix, and as a result of the fundamentally enhanced reaction wave propagation mechanism of inner body surface radiation coupled with forced convection and inner matrix solids thermal conduction, it is believed that the matrix burning velocity of the mixture in the matrix may be independent of, or at least more independent of, the system pressure than the burning velocity of an identical mixture by conventional incineration. This is an improvement over conventional combustors wherein the laminar flame speed of fuel mixtures in air decreases significantly with increasing system pressure. See Egolfopoulos et al., "Laminar Flame Speeds of Methane-Air Mixtures Under Reduced and Elevated Temperatures,"76 COMBUSTION AND FLAME 375 (1989). According to the present invention, the combustion intensity of reacting gases through a unit cross-sectional area would increase directly with pressure, since the mass flow of gases would increase directly with pressure, and the matrix burning velocity is not expected to decrease with pressure. The non-negative dependence of matrix burning velocity on pressure is expected to be a result of one or both of the phenomena of in-matrix, backward-propagating, inner-body surface radiation of heat, and forced-convection of heat from the solid matrix to the incoming gases.

#As a result of the laminar and plug flow characteristics of this process, and the good distribution of heat resulting from the intra-matrix surface radiation coupled with surface convection, the combustion of the fuel is more complete than flame combustion. According to the present invention, the fuel mixture is heated by heat generated by the reaction, further increasing the completeness of the reaction.