Chemistry of inorganic compounds – Nitrogen or compound thereof – Ammonia or ammonium hydroxide
Reexamination Certificate
1998-09-08
2001-05-08
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Nitrogen or compound thereof
Ammonia or ammonium hydroxide
C423S360000, C423S361000
Reexamination Certificate
active
06228341
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to plate type exchangers for cooling a reaction zone by indirect heat exchange with a cooling fluid stream.
BACKGROUND OF THE INVENTION
In many industries, like the petrochemical and chemical industries, contact of reaction fluids with a catalyst in a reactor under suitable temperature and pressure conditions effects a reaction between the components of one or more reactants in the fluids. Most of these reactions generate or absorb heat to various extents and are, therefore, exothermic or endothermic. The heating or chilling effects associated with exothermic or endothermic reactions can positively or negatively affect the operation of the reaction zone. The negative effects can include among other things: poor product production, deactivation of the catalyst, production of unwanted by-products and, in extreme cases, damage to the reaction vessel and associated piping. More typically, the undesired effects associated with temperature changes will reduce the selectivity or yield of products from the reaction zone. The heating of reactants may be useful for a variety of exothermic and endothermic processes. Dehydrogenation processes represent one class of endothermic processes that particularly benefit from indirect reaction zone heating to maintain a desired temperature profile.
This invention is particularly suited for exothermic processes. Exothermic reaction processes encompass a wide variety of feedstocks and products. Moderately exothermic processes include methanol synthesis, ammonia synthesis, and the conversion of methanol to olefins, phthalic anhydride manufacture by naphthalene orthoxylene oxidation, acrylonitrile production from propane or propylene, acrylic acid synthesis from acrolein, conversion of n-butane to maleic anhydride, the production of acetic acid by methanol carbonylation and methanol conversion to formaldehyde. Oxidation reactions generally represent a class of highly exothermic reactions. The exothermic nature of these reactions has led to many of these reactions incorporating a cooling system into the reactor design. Those skilled in the art routinely overcome the exothermic heat production with quench or heat exchange arrangements. Extensive teachings detail methods of indirectly exchanging heat between the reaction zone and a cooling medium. The art currently relies heavily on tube arrangements to contain the reaction and supply indirect contact with the cooling medium. The geometry of tubular reactors poses layout constraints that require large reactors and vast tube surface to achieve high heat transfer efficiencies.
Other process applications accomplish indirect heat exchange with thin plates that define channels. The channels alternately retain catalyst and reactants in one set of channels and a heat transfer fluid in adjacent channels for indirectly heating or cooling the reactants and catalysts. Heat exchange plates in these indirect heat exchange reactors can be flat or curved and may have surface variations such as corrugations to increase heat transfer between the heat transfer fluids and the reactants and catalysts. Many hydrocarbon conversion processes will operate more advantageously by maintaining a temperature profile that differs from that created by the heat of reaction. In many reactions, the most beneficial temperature profile will be obtained by maintaining substantially isothermal conditions. In some cases, a temperature profile directionally opposite to the temperature changes associated with the heat of reaction will provide the most beneficial conditions. For such reasons it is generally known to contact reactants with a heat exchange medium in cross flow, cocurrent flow, or countercurrent flow arrangements. A specific arrangement for heat transfer and reactant channels that offers more complete temperature control can be found in U.S. Pat. No. 5,525,311; the contents of which are hereby incorporated by reference. Other useful plate arrangements for indirect heat transfer are disclosed in U.S. Pat. No. 5,130,106 and U.S. Pat. No. 5,405,586.
Isolating reactants from coolants at the inlets and outlets of a plate exchanger arrangement leads to elaborate designs and intricate manufacturing procedures. Simplification of the fluid transfer at the inlets and outlets of a plate exchanger arrangement improves the cost effectiveness of and practicality of such arrangements in many processes.
It is, therefore, an object of this invention to simplify plate exchanger arrangements for the cooling of an exothermic reaction zone by indirect heat transfer.
It is a further object of this invention to simplify the feed and recovery of reactants and coolants from a heat exchange reactor using narrow channels.
BRIEF SUMMARY OF THE INVENTION
This invention incorporates open chamber portions to transfer fluid for indirectly transferring heat produced in the reaction channels to the heated channels that absorb heat by raising the temperature of a reactant-containing stream. A chamber communicates the ends of the channels to provide simple transfer of the heated channels with the reaction zone across common ends of the narrow channels. The chamber permits additional temperature control by the addition or removal of reactants and by cooling fluids or other streams at an intermediate point along the total channel flow path. Insertion of additional chambers along the flow path of either the reaction or heated channels provides locations for more temperature adjustment and control.
Suitable channel arrangements may exchange heat directly across a common heat exchange surface or may use an intermediate heat transfer fluid to transfer heat from the cooling zone to the reaction zone while simultaneously providing temperature adjustment control. One arrangement of the intermediate heat transfer fluid may place the cooling zone and the reaction zone at different portions of common channels and may pass the intermediate fluid through adjacent channels to transfer heat out of reaction channels at one location and transfer heat back into the heated channels at a downstream channel location. In other arrangements the intermediate channels and the reaction channel may lie in a parallel arrangement between the heated channels to adjust the temperature in the reaction channels through the heated channels.
In most cases the reactant-containing stream will pass through the heated channels and then directly into the reaction channels to provide continuous fluid flow through all channels with an essentially constant pressure in all of the channels. Circulation of the reactant-containing stream around the outer shell of the vessel that contains the channel defining plates can offer further temperature control. Appropriate processes may also incorporate an endothermic reaction into the heated channels to further control temperatures.
The resulting reaction apparatus designed in accordance with this invention offers flexibility in temperature control with a relatively simple plate reactor arrangement. The outer containment vessel can completely support the plate arrangement from either its top or its bottom. Direct passage of heated reactants from the heated channels to the reaction channel from common ends in a chamber eliminates welding at least one end of multiple thin plates.
The presence of narrow heat exchange channels for cooling the reaction zone and for heating the reactants constitutes an essential requirement of this invention. With respect to fluid flow through the reaction channels and heated channels, the fluids may have cocurrent flow or cross flow with respect to some of the channels. However, advantageous use of the chamber design of this invention requires that at least two adjacent sets of channels establish countercurrent flow.
Variations in the catalyst loading within the reaction channels and the addition of catalyst for endothermic reactions may satisfy different processing objectives. For example, short loading of catalyst in reaction channels can provide a space above or below the reaction zo
Hebert Philippe
Pujado Peter R.
Romatier Jacques J. L.
Vora Bipin V.
Griffin Steven P.
Medina Maribel
Paschall James C.
Tolomei John G.
UOP LLC
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