GB2114148A - Hydrorefining and/hydrocracking heavy hydrocarbon feeds - Google Patents

Abstract

The raw hydrocarbon material (1) is separated into a plurality e.g. four component streams identical in number with the number of strands in a multi-strand furnace (F) preceding a catalytic reactor (G), and they are mixed with gases (2) containing hydrogen likewise previously separated into an equal number of streams at temperatures below 520 DEG K. After preheating the mixed raw materials and gases in counter- current with the reaction products leaving the reactor (G), and subsequently heating further in the furnace (F) to reaction temperature, the streams are fed into the reactor (G). After reaction and cooling by heat exchange (in B, C, D, E) with the materials being preheated, the temperature of the reaction mixture is adjusted to enable separation favourable from the energy point of view by heat exchange (in A) with the infeed of raw material before separation of the latter into the component streams. <IMAGE>

Description

SPECIFICATION Method of converting hydrocarbon fractions into useful products The invention relates to a method of converting hydrocarbon fractions into useful products including fuel oil components, fuel components, raw materials for the production of fuels, and crude or intermediate petrochemical products.

The hydrocarbon fractions are converted partially or wholly in the liquid phase in the presence of gases including hydrogen, and one or more catalysts. This present method is used in the processes of hydrorefining and/or hydrocracking of hydrocarbon fractions.

It is known that petroleum fractions can be converted by means of catalytic hydrorefining and/or catalytic hydrocracking into fuel components, fuel-oil components, raw materials for the production of fuels or crude or intermediate petrochemical products.

The known methods of hydrorefining, as described, for example, in Chemical Engineering Progress 61, Oct. 1965, pages 77-82, ibidem 63 Sept. 1967; Oil and Gas Journal 19.5.1969, pages 131-139, ibiden 16.5.1977, pages 146-165; Bulletin of the Japan Petroleum Institute Vol. 13, No. 1, May 1971, Hydrocarbon Processing Vol. 51, No. 9, Sept 1972, pages 1 54-1 64, ibidem Vol. 53, No. 9, Sept. 1974, pages 140-151, ibidem Vol. 58, No. 10, Oct.

1979, pages 137-142, US-P 34 15 737, US-P 3668 112, US-P 36 91 059, US-P 36 91 067, and DE-OS 23 30 385 require as reaction conditions pressures between 1 and 20 MPa, temperatures between 5500K and 720"K and recycle-gas/product ratios of 100 to 2000 m3iN/m3.

The known methods of hydrocracking, as described, for example, in the US-P 36 20 962, in Oil and Gas Journal 20.3.1967 page 170, ibidem 31.5.1971, pages 70-73, Hydrocarbon Processing, Vol. 51, No. 9, Sept. 1972, pages 139-146, Ibidem Vol. 53, No. 9, Sept. 1974, pages 126-132 and ibidem Voi. 57, No. 5, May 1978, pages 117-121, all work in the reaction zone at pressures between 5 and 25 MPa, temperatures between 5800K and 7300K and recycle-gas/product ratios between 500 and 3000 m3iN/m3.

According to the Petroleum Processing Handbook 1967, McGraw-Hill Inc. pages 5-16, with hydrogen partial pressures above 0.7 MPa, the use of cost-favourable carbon steels for plant construction is only possible in lower temperature ranges. Thus, particularly at the temperatures above 4700 K, depending on the partial pressures of hydrogen sulphide and hydrogen, the use of expensive, high-alloy steels for hydrorefining or hydrocracking plant becomes desirable if not necessary, and so such plant consists of a considerable proportion of high-alloy steels.

In order to bring the raw materials to be converted and gases containing hydrogen to the required reaction temperature, they are usually heated by heat exchange with the reaction products and by heating in gas-fired or oil-fired furnaces. The utilization of the heat content of the reaction products to heat the raw materials to be converted and the gases containing hydrogen is carried as far as possible in order to minimize energy input requirements, and in many cases the reagents are heated to a few degrees below the necessary reaction temperature by heat exchange alone. In every case, however, a separate furnace is still necessary to adjust the necessary reaction temperature.

The separation of the reaction products is effected in steps, as is known, in hot separators and cold separators, and according to DD-WP 148 887, washing the recycle gas with a component amount of the corresponding cold separation condensate is desirable.

Attainment of the required separating conditions is usually realised by a partial bypassing of the heat exchanger, as illustrated in Figure 1, which is described in more detail hereinafter. Bypass regulation has the disadvantage that relatively cold and relatively hot products with hydrogen partial pressures above 0.7 MPa, meet one another under conditions which are important as regards the selection of constructional material for the plant and so as regards the costs. Accordingly, problems of the material stability arise unless expensive solutions and/or designs for higher temperature are adopted.

With the sizes of plant usual today, of between 500 and 3000 Kt of raw material per annum, the heat exchanger between reactor inlet and reactor outlet mixtures is of single strand type even if the transfer of the amounts of heat necessitates the connecting in series of a plurality of heatexchangers. The furnace necessary in every plant is at least two strand for limiting pressure losses and more particularly because of the maximum permissible furnace tube diameter. Limitation of the tube diameter of the furnace coils stems in particular from such factors as the maximum permissible heating surface loading, maximum permissible internal temperature of the tubes, maximum permissible temperature gradient in the medium over the tube cross-section both for process reasons and for reasons of cost and through the technical possibilities.

Since the petroleum fractions used in the hydrorefining or hydrocracking methods are evaporated only partially or scarcely at all under the reaction conditions, the mixture of hydrogen and hydrocarbon to be heated in the furnace is two-phase. The consequence of this is that in the practical operation of the furnaces, uniform distribution of the mixture of gas and liquid between the individual furnace strands cannot be achieved. This phenomenon becomes particularly significant when the minimum proportion of recycle gas containing hydrogen is employed, as is otherwise aimed for, for energy reasons. The non-uniform feed to the strands leads to local overheating, unwanted cracking and condensation reactions, and coking, and ultimately to the blocking of individual tube coils therefore, so that the operation has to be interrupted.Also the mixture of hydrocarbons tends increasingly to coke formation and the formation of deposits on the catalyst in the following reaction zone. This leads to an increase in pressure loss in the reactor and a loss of activity in the catalyst. Since a uniform admission of the mixture of gas and liquid to the furnace strands by means of quantity regulation has not been possible with the technical means hitherto available, in the pressure and temperature range of interest, in some cases separate heating of the gases containing hydrogen, and of the petroleum fraction partially or wholly in the liquid phase, has been adopted in separate furnaces as an alternative. See, inter alia, Hydrocarbon Processing Vol. 58, No. 5, May 1979, page 108.

This technological approach is uneconomical in terms of costs and energy because of the use of two furnaces. The heating of the petroleum fractions to temperatures above 6000K in the absence of hydrogen leads to the risk of unwanted cracking and coking reactions. In addition, this technological approach fails to provide a solution favourable from the energy and cost point of view to the regulation of the conditions for the separation of the reaction products.

An object of the present invention is to provide an efficient method of converting hydrocarbon fractions which are partially or wholly in the liquid phase, in the presence of gases containing hydrogen and of one or more catalysts into useful products such as fuel-oii components, fuel components, raw materials for the production of fuels or crude and intermediate petrochemical products with improved technical characteristics and economy, and with increased reliability and flexibility in the large-scale process of hydrorefining and/or hydrocracking.

The method of conversion is made more effective and more reliable in operation by alterations in the process of hydrorefining and/or hydrocracking.

According to the present invention, there is provided a method of converting hydrocarbon fractions in the process of hydrorefining and/or hydrocracking, wherein the raw material for conversion is partially or wholly in the liquid phase, and is converted in the presence of gases containing hydrogen and of one of more catalysts, the method including the steps of dividing the raw material, with quantity regulation, into a plurality of streams equal in number to the number of strands in a plural-strand furnace preceding a conversion reactor, dividing the gases containing hydrogen, with quantity regulation, into an equal number of streams at hydrogen partial pressures above 0.7 MPa and at temperatures below 5200 K, combining the gas streams with respective raw material streams to form a plurality of component streams, heating the component streams in countercurrent with reaction products leaving the reactor and subsequently in the plural-strand furnace to a predetermined reaction temperature and admitting the heated reactants to the reactor, after the reaction has been effected, the ensuing products being cooled by heat exchange with the component streams approaching the furnace and ultimately separated, the conditions for separation of the products to achieve a separation favourable from the energy point of view, being adjusted by heat exchange with the stream of raw material prior to division thereof into the plurality of streams thereof, above 4100K.

Thus, in practising the invention, the raw materials, which is partially or wholly in the liquid phase and which consists essentially'of hydrocarbons, is divided into at least two component streams and the quantity in each is regulated.

There are as many streams as there are strands in the furnace preceding the reactor. These streams are mixed with gases containing hydrogen and previously separated, with regulation of the amount thereof into an equal number of component streams at hydrogen partial pressures above 0.7 MPa and temperatures below 5200K.

The mixtures are then first heated in countercurrent with the reaction products and subsequently in a furnace to reaction temperature. After the reaction has been effected, the reaction products are cooled by heat exchange with the infed reactants. The conditions for a separation of the reaction mixture favourable from an energy point of view are adjusted by heat exchange with the stream of raw material which has not yet been separated, above 410"K.

In the preferred practice of the invention, the reaction products are divided into a plurality of streams and fed into respective heat exchangers upstream of the furnace for cooling by exchange with the said component streams before admission of the latter to the furnace, the products being further cooled to a predetermined separation temperature, before admission to the separator, in a further heat exchanger by heat exchange with the raw material infeed, adjustment of the separation temperature being obtained by controlled by-passing of the further heat exchanger by a metered portion of the raw material infeed. Conveniently, the temperature of the reaction products leaving the further heat exchanger is monitored and a valve in a by-pass line for the said portion of the infeed is controlled in response to the monitored temperature.

The invention comprehends plant for use in practising the method according to the invention.

Accordingly, there is provided plant comprising means for separating the raw material infeed into a plurality of streams thereof, means to control the flow rates of said raw material streams, means for separating the gases containing hydrogen into an equal plurality of streams each having hydrogen partial pressures above 0.7 MPa and temperatures below 5200K and means for controlling the flow rates of the gas streams, means to combine the gas streams each with a respective one of the raw material streams to provide a plurality of component streams, heat exchangers to elevate the temperatures of the component streams by heat exchange with reaction products obtained after conversion of the raw material, and a plural-strand furnace preceding a catalytic converter in which said products are generated, the temperatures of the heated component streams being raised to the predetermined reaction temperature as each passes through a respective furnace strand allotted thereto, there being means to feed the reaction products leaving the converter to the said heat exchangers and then to a final heat exchanger preceding a separating means which separates liquid and gaseous reaction products, the final heat exchanger being located in an infeed line for the raw material upstream of the means which separate the raw material into the said streams thereof.

Preferably, the final heat exchanger has a controlled by-pass line whereby a portion of the raw material infeed can by-pass the heat exchanger, and means to control said by-pass line so as to establish a predetermined temperature in the reaction products leaving the final heat exchanger.

The invention will now be explained in more detail by way of example, first with reference to the prior art; the following description makes reference to the accompanying drawings, in which: Fig. 1 is a schematic illustration of plant and process conditions of the prior art, and Fig. 2 is a schematic illustration of plant and process conditions for practising the present invention.

Variant (Fig. 1) Variant 1 relates to the known technology for converting hydrocarbon fractions in the presence of gases containing hydrogen and of one or more catalysts.

As illustrated in Figure 1, a heavy petroleum fraction 1 at 463 OK and gas containing hydrogen at 4330K and 6.84 MPa are mixed, heated to 6330K in the serially-connected heat-exchangers A, B, C, D and E. On entry into the furnace F, the mixture is distributed as four component streams between the furnace strands without regulation.

In the furnace F, the mixture is so heated that, when the streams leaving the furnace are recombined, the temperature of the mixture is 668cm. As a result of the non-uniform distribution of the mixture of gas and liquid, the furnace outlet temperatures of the individual strands differ, and are at 7030K, 6500K, 6830K and 6560K. The hydrocatalytic conversion then takes place in the reaction G at 6.0 MPa. Because the reactions there take place predominantly exothermally, the mixture of reaction products leaves the reactor G at 6830K and is cooled as it passes in turn through the jacket spaces of the heat-exchangers E, D, C, B and A to a separating temperature for the hot separator H of 51 30K, which is favourable from the energy point of view for separating the gas product 3 from the liquid product 4.

Adjustment and adherence to the required temperature of 51 30K in the hot separator H is realized by partial by-passing of the exchangers A, B, C, D and E. To this end, some of the heavy petroleum fraction 1 is led past the heat exchangers for adding to the mixture of gas and liquid prior to admission to the furnace F.

The ratio of the pressures of the gas 2 upstream of the mixing point and of the gas 3 leaving the hot separator H, which is decisive for the compression of the gases 2 containing hydrogen and circulated, amounts to 6.84 MPa =1.21708.

5.62 MPa The pressure difference amounts to 1.22 MPa.

These values relate to a running time for the plant of 180 days with the use of 200 m3/h of heavy petroleum distillate and 80,000 m3iN/h of gases containing hydrogen. This amount of gas was adjusted on the 124th day, after the plant had to be taken out of service on the 11 8th day because of blockage of one furnace strand with the original amount of gas of 60,000 m3iN/h.

Variant 2 (Fig. 2) Variant 2 corresponds to the method according to the invention.

As illustrated in Figure 2, a heavy petroleum fraction 1 at 463 OK is heated in the tube compartment of the heat-exchanger A to 5030K by heat exchange with the mixture of reaction products. The fraction 1 is then separated, with quantity regulation, into four equal component streams and mixed with four streams of gases 2 containing hydrogen. The said gas streams are likewise separated, with quantity regulation, into four equal component streams from a gas infeed at 6.36 MPa and 4330K.The mixed components are then heated, in four parallel strands, in each of the heat-exchangers B, C, D and E to 6330K and in the four-strand furnace F to the reactor inlet temperature of 6680K. The furnace outlet temperatures for the individual strands, which are extremely close to one another, are 668.80K, 667.70K, 668.1 0K and 667.50K, proving that there is a very uniform distribution of the mixture of gas and liquid between the individual furnace strands so that local overheating through different stream amounts is excluded. The hydrocatalytic conversion is effected in the reactor G at 6.0 MPa.

The mixture of reaction products leaves the reactor at 6830K and is cooled to 5380K in the jacket spaces of the heat exchangers B, C, D and E. The separation conditions favourable from the energy point of view for separating the gas product 3 from the liquid product 4 in the hot separator H are adjusted by means of heat exchange with the heavy petroleum fraction 1 in the heat exchanger A, there being the possibility of a partial by-passing with the heavy petroleum fraction 1. The hot separator H works at 51 30K and 5.84 MPa.

The ratio of the pressures of the gas2 containing hydrogen before the mixing with the heavy petroleum fraction 1 and of the gas 3 leaving the separator H amounts to 6.36 MPa =1.08904.

5.84 MPa The pressure difference is 0.52 MPa. These values relate to the 180th day of running the installation with at200 m3/h input of heavy petroleum fraction and 60,000 m3iN/h of gases containing hydrogen and circulated. This plant was operated up till then in an uninterrupted sequence; no problems arose.

The advantages of the method according to the invention, compared with Variant 1 are: (i) greater reliability and trouble-free oDeration with the use of the heaviest petroleum fractions and minimum circulation of gases containing hydrogen; (ii) reduction of the minimum amount of recycle gas necessary by 25%; (iii) exclusion of local overheating in the furnace tubes through unequal reactant admission and so prevention of strand blockages or a severe rise in pressure loss in the furnace and reactor; (iv) reduction in the tendency of the reactants to coking and so longer catalyst life is attained; (v) improvement in the product quality or the achievement of a higher degree of conversion; ; (vi) lower energy consumption resulting particularly from the 25% smaller amount of recycle gas necessary and the energy consumption in compression, which is reduced by 60% because of the lower input to output pressure ratio.

Claims (8)

Claims

1. A method of converting hydrocarbon fractions in the process of hydrorefining and/or hydrocracking, wherein the raw material for conversion is partially or wholly in the liquid phase, and is converted in the presence of gases containing hydrogen and of one or more catalysts, the method including the steps of dividing the raw material, with quantity regulation, into a plurality of streams equal in number to the number of strands in a plural-strand furnace preceding a conversion reactor, dividing the gases containing hydrogen, with quantity regulation, into an equal number of streams at hydrogen partial pressures above 0.7 MPa and at temperatures below 5200K, combining the gas streams with respective raw material streams to form a plurality of component streams, heating the component streams in countercurrent with reaction products leaving the reactor and subsequently in the pluralstrand furnace to a predetermined reaction temperature and admitting the heated reactants to the reactor, after the reaction has been effected, the ensuing products being cooled by heat exchange with the component streams approaching the furnace and ultimately separated, the conditions for separation of the products to achieve a separation favourable from the energy point of view, being adjusted by heat exchange with the stream of raw material prior to division thereof into the plurality of streams thereof, above 4100K.

2. A method according to claim 1, wherein the reaction products are divided into a plurality of streams and fed into respective heat exchangers upstream of the furnace for cooling by exchange with the said component streams before admission of the latter to the furnace, the products being further cooled to a predetermined separation temperature before admission to the separator, in a further heat exchanger by heat exchange with the raw material infeed, adjustment of the separation temperature being obtained by controlled by-passing of the further heat exchanger by a metered portion of the raw material infeed.

3. A method according to claim 2, wherein the temperature of the reaction products leaving the further heat exchanger is monitored and a valve in a by-pass line for the said portion of the infeed is controlled in response to the monitored temperature.

4. Plant for practicing the method according to claim 1, comprising means for separating the raw material infeed into a plurality of streams thereof, means to control the flow rates of said raw material streams, means for separating the gases containing hydrogen into an equal plurality of streams each having hydrogen partial pressures above 0.7 MPa and temperatures below 5200K and means for controlling the flow rates of the gas streams, means to combine the gas streams each with a respective one of the raw material streams to provide a plurality of component streams, heat exchangers to elevate the temperatures of the component streams by heat exchange with reaction products obtained after conversion of the raw material, and a pluraistrand furnace preceding a catalytic converter in which said products are generated, the temperatures of the heated component streams being raised to the predetermined reaction temperature as each passes through a respective furnace strand allotted thereto, there being means to feed the reaction products leaving the converter to the said heat exchangers and then to a final heat exchanger preceding a separating means which separates liquid and gaseous .reaction products, the final heat exchanger being located in an infeed line for the raw material upstream of the means which separate the raw material into the said streams thereof.

5. Plant according to claim 4, wherein the final heat exchanger has a controlled by-pass line whereby a portion of the raw material infeed can by-pass the heat exchanger, and means to control said by-pass line so as to establish a predetermined temperature in the reaction products leaving the final heat exchanger.

6. Plant according to claim 5, wherein the bypass line has a control valve therein and a reaction product line between the final heat exchanger and the separating means has temperature monitoring means therein which serves to control said control valve.

7. A method according to claim 1 and substantially as herein described with reference to and as shown in Fig. 2 of the accompanying drawings.

8. Plant according to claim 4 constructed and arranged to function as herein described with reference to Variant 2 and Fig. 2 of the accompanying drawings.