Method for revamping a conventional mineral oils refinery to a biorefinery

Abstract

The invention relates to a method for revamping a conventional refinery of mineral oils into a biorefinery, characterized by a production scheme which allows the treatment of raw materials of a biological origin (vegetable oils, animal fats, exhausted cooking oils) for the production of biofuels, prevalently high-quality biodiesel. This method allows the re-use of existing plants, allowing, in particular, the revamping of a refinery containing a system comprising two hydrodesulfurization units, U1 and U2, into a biorefinery containing a production unit of hydrocarbon fractions from mixtures of a biological origin containing fatty acid esters by means of their hydrodeoxygenation and isomerization, wherein each of the hydrodesulfurization units U1 and U2 comprises: a hydrodesulfurization reactor, (A1) for the unit U1 and (A2) for the unit U2, wherein said reactor contains a hydrodesulfurization catalyst; one or more heat exchangers between the feedstock and effluent of the reactor; a heating system of the feedstock upstream of the reactor; an acid gas treatment unit downstream of the reactor, containing an absorbent (B) for H2S, said unit being called T1 in the unit U1 and T2 in the unit U2, and wherein said method comprises: installing a line L between the units U1 and U2 which connects them in series; installing a recycling line of the product for the unit U1 and possibly for the unit U2, substituting the hydrodesulfurization catalyst in the reactor A1 with a hydrodeoxygenation catalyst; substituting the hydrodesulfurization catalyst in the reactor A2 with an isomerization catalyst; installing a y-pass line X of the acid gas treatment unit T2 of the unit U2; substituting the absorbent (B) in the acid gas treatment unit T1 with a specific absorbent for C02 and H2S. The operative configuration obtained with the method, object of the present invention, also leads to a substantial reduction in emissions of pollutants into the atmosphere, with respect to the original operative mode. The invention also relates to the transformation unit of mixtures of a biological origin obtained with said conversion method and particularly hydrodeoxygenation and isomerization processes.

Claims

1. A method for revamping a refinery comprising a system comprising two hydrodesulfurization units, (U1) and (U2), into a biorefinery comprising a production unit of hydrocarbon fractions from mixtures of a biological origin comprising fatty acid esters by means of their hydrodeoxygenation and isomerization, wherein each of the hydrodesulfurization units (U1) and (U2) comprises: a hydrodesulfurization reactor, (A1) for the unit (U1) and (A2) for the unit (U2), wherein the reactor comprises a hydrodesulfurization catalyst; a heat exchanger between a feedstock and effluent of the reactor; a heating system of the feedstock upstream of the reactor; an acid gas treatment unit downstream of the reactor, comprising an absorbent (B) for H.sub.2S, (T1) in the unit (U1) and (T2) in the unit a (U2), the method comprising: installing a line L between the units (U1) and (U2) which connects them in series; installing a recycling line of the product for the unit (U1) and optionally for the unit (U2), substituting the hydrodesulfurization catalyst in the reactor (A1) with a hydrodeoxygenation catalyst; substituting the hydrodesulfurization catalyst in the reactor (A2) with an isomerization catalyst; installing a by-pass line (X) of the acid gas treatment unit (T2) of the unit (U2); and substituting the absorbent (B) in the acid gas treatment unit (T1) with a specific absorbent for CO.sub.2 and H.sub.2S.

2. The method according to claim 1, wherein the biorefinery comprises a HDO/ISO unit, and wherein the method further comprises: installing an acid gas treatment unit (T3) downstream of the acid gas treatment unit (T1) to separate the H.sub.2S; and recycling the H.sub.2S to the reactor (A1).

3. The method according to claim 1, wherein units (U1) and (U2) are employed, comprising hydrogen recycling lines which connect the acid gas treatment units (T1) and (T2) with the reactors (A1) and (A2).

4. The method according to claim 1, wherein each of the hydrodesulfurization units (U1) and (U2) further comprises: a hydrogen recycling line and a compressor on the line, (K1) for the unit (U1) and (K2) for the unit (U2), and wherein the method comprises: installing an acid gas treatment unit (T3) downstream of the acid gas treatment unit (T1); and installing a recycling line (R3) of H.sub.2S from the unit (T3) to the compressor (K1) of the hydrogen recycling line of the unit (U1).

5. The method according to claim 4, wherein the acid gas treatment unit (T3) comprises two absorbing areas each comprising a specific absorbent for CO.sub.2.

6. The method according to claim 1, comprising: connecting the unit (U1) to a sulfur recovery unit comprising a thermal section and a catalytic section by the installation, from the unit (T1) of (U1), of a by-pass line of the thermal section of the sulfur recovery unit; and substituting the catalyst of the first reactor of the catalytic section of the sulfur recovery unit with a cold selective redox catalyst.

7. The method according to claim 1, wherein a surge drum (S) is installed upstream of each of the reactors (A1) and (A2).

8. The method according to claim 1, wherein units (U1) and (U2) comprising high-pressure separators, low-pressure separators, stripping columns and optionally driers, are employed.

9. The method according to claim 1, wherein units (U1) and (U2) are employed, comprising lines for feeding make-up hydrogen, optionally after mixing with recycled hydrogen, to each of the reactors (A1) and (A2) and/or comprising gas separation/washing downstream of each of the reactors (A1) and (A2).

10. The method according to claim 9, wherein the hydrogen feeding lines come from reforming units.

11. The method according to claim 1, wherein the hydrocarbon fractions are obtained from the biorefinery are fuels or fuel components.

12. The method according to claim 11, wherein the fuels or fuel components that are obtained from the biorefinery are LPG, kerosene, diesel, or naphtha.

Description

(1) FIG. 1 shows a scheme example relating to the HDO/ISO unit deriving from the revamping method of the present invention: the dashed parts and lines correspond to the new installations according to the method of the present invention, whereas the continuous parts and lines correspond to the pre-existing hydrodesulfurization equipments.

(2) In particular, in FIG. 1, Feed is the mixture of a biological origin which is fed to the HDO/ISO unit, where said mixture can be, for example, a refined vegetable oil, i.e. with a content of fatty acids not higher than 1,000 ppm by weight.

(3) The fresh feedstock of vegetable oil is fed through line 1 to the surge drum S1 after mixing with part of the reaction product which is recycled through line R1: equalization of the feedstock composed of fresh feed and the fraction of recycled product therefore takes place in S1.

(4) The feedstock leaving S1 reaches the feed-effluent exchanger E1 through line 2, where the pump P1 is located.

(5) The heat exchange between the feedstock and the product leaving the reactor A1 takes place in E1. The feedstock reaches the hydrogen feeding line 4 through line 3, and the mixture of hydrogen and feed is fed to the reactor A1 through line 5: the oven F1 that heats the mixture to the reaction temperature is situated on this line.

(6) The hydrodeoxygenation product leaving the reactor reaches the exchanger E1 through line 6 and subsequently reaches the air exchanger a through line 7 and the high-pressure separator H1 through line 7a. The separation of the water SW, of the hydrocarbon fraction formed during the hydrodeoxygenation step and of the gaseous mixture prevalently consisting of H.sub.2, H.sub.2S and CO.sub.2, takes place in said separator H1. The hydrocarbon fraction is sent through line 8 to the low-pressure separator L1. The mixture of H.sub.2, H.sub.2S and CO.sub.2 is sent through line 9 to the acid gas treatment unit T1. The CO.sub.2 and H.sub.2S are absorbed in this acid gas unit T1 by means of a specific absorbent and said absorbent is regenerated: a stream of hydrogen and a stream of CO.sub.2 and H.sub.2S are therefore obtained at the outlet of the unit T1. The stream of hydrogen reaches line 11 through line 10, which feeds hydrogen deriving from an internal source of the refinery, for example a reforming unit. The compressors K1 and K2 are present on line 10 and line 11 respectively. The hydrogen comes from line I which represents the hydrogen supply network of the refinery. The resulting hydrogen flow reaches the feed line 3 through line 4. Lines 4a and 4b branch off from line 4, which allow part of the hydrogen to be fed at different heights of the reactor also obtaining a quenching effect. The stream of CO.sub.2 and H.sub.2S at the outlet of the unit T1 reaches the acid gas treatment unit T3 through line 12.

(7) The separation of CO.sub.2 and H.sub.2S takes place in said acid gas unit T3 through two absorption steps with specific absorbents and their respective regeneration: a stream of H.sub.2S and a stream of CO.sub.2 are therefore obtained at the outlet of the unit T3.

(8) The stream of H.sub.2S leaving T3 reaches the suction of the compressor K1, through the line R3, where the hydrogen flow of line 10 also arrives.

(9) The stream of CO.sub.2 leaving T3 is fed, through line 13, to the final thermo-combustor of the Claus plant or is sent to one of the refinery ovens suitably equipped with specific flues for the insertion of said stream.

(10) A further separation of water SW takes place in the low-pressure separator L1, together with the separation from the hydrocarbon mixture from the Fuel Gas (FG), which is removed through line 41. The hydrocarbon mixture is then sent to the fractionation column C1 through line 14, on which the exchanger b is situated.

(11) At the head of the fractionation column, line 29 brings a mixture of gas rich in propane and water to the condenser a1. Said mixture is fed through line 30 to an accumulator M, where it is carried out the separation of the water, of the gas rich in propane which is removed through line 31 and of the liquid used as reflux in the fractionation column C1, through line 32 and the pump P3. The gas rich in propane is indicated as LPG as it reaches the specifications of commercial LPG after a washing with amines not shown in the FIGURE.

(12) A hydrocarbon fraction substantially containing linear paraffins having a number of carbon atoms which depends on the type of feed used, is separated from the bottom of the fractionation column. Said hydrocarbon fraction reaches the vacuum dryer V1 by means of line 15 on which the exchanger c is situated. The flow of hydrocarbon product leaving V1, passes through line 16 into the pump d and then to the exchanger and through line 17, before being partly fed to the subsequent isomerization section through line L and partly recycled into the feed through line R1.

(13) The hydrocarbon product of the HDO section leaving the exchanger is fed through line L to the surge drum S2. The recycling line R2 of the isomerization product is inserted on line L and equalization of the feed is obtained in S2.

(14) The feed leaving S2 reaches the exchanger E2 through line 18 on which the pump P2 is situated.

(15) The heat exchange between the feed and the product leaving the reactor A2 takes place in E2. The feed reaches the hydrogen feeding line 20, through line 19, and the mixture of hydrogen and feed is fed through line 21 to the reactor A2: the oven F2 which heats the mixture to the reaction temperature is situated on said line.

(16) The isomerization product leaving the reactor A2 reaches the exchanger E2 through line 22 and subsequently reaches the air exchanger a2 through line 23 and the high-pressure separator H2 through line 24. The separation of the water SW, of the isomerized hydrocarbon fraction formed during the isomerization step and of hydrogen takes place in said separator H2. The hydrocarbon fraction is sent through line 25 to the low-pressure separator L2. The stream of hydrogen leaves the separator H2 through line 26 and said line 26 joins the line X, whose function is to by-pass the acid gas treatment unit T2. T2 is part of the hydrodesulfurization unit which has been revamped and is not used in the new HDO/ISO unit. The line X therefore allows the hydrogen flow not to pass through T2 and joins line 27, through which the hydrogen flow reaches line 28, which feeds hydrogen deriving from an internal source of the refinery, for example a reforming unit. The compressors K3 and K4 are present on line 27 and 28 respectively. The resulting hydrogen flow reaches the feed line 19 through line 20. The existing lines 20a and 20b branch off from line 20, which allow part of the hydrogen to be fed at different heights of the isomerization reactor also obtaining a quenching effect.

(17) A further separation takes place in the low-pressure separator L2, of the water SW from the isomerized hydrocarbon mixture and from the Fuel Gas (FG) which is removed by means of line 33. The isomerized hydrocarbon mixture is then sent to the fractionation column C2 by means of line 34, on which the exchanger b2 is situated. An isomerized hydrocarbon fraction is separated from the bottom of the fractionation column. Said hydrocarbon fraction reaches the vacuum dryer V2 through line 35 on which the exchanger s is situated. The flow of isomerized hydrocarbon product, through line 36, is fed to the pump P3: the flow leaving the pump is partly recovered and partly recycled through line R2 to the line L. The product recovered is a high-quality diesel of a biological origin (Green Diesel).

(18) At the head of the fractionation column C2, the line 37 brings a mixture of fuel gas and naphtha to the exchanger a3. Said mixture is fed through line 38 to an accumulator Ml. The Fuel Gas is separated from the naphtha in said accumulator Ml. The fuel gas is removed through line 39 which joins line 25.

(19) The naphtha is partly recycled, through line 40, on which the pump P4 is situated, to the fractionation column C2, (line 40a) and partly recovered as high-quality naphtha of a biological origin (Green Naphtha).

(20) A method has therefore been found for transforming hydrodesulfurization units into conversion units of mixtures of a biological origin based on fatty acid esters into fuel bases, whose main product is diesel and diesel component, in addition to naphtha and LPG, with minimum variations in the equipment already existing and a limited number of suitably selected substitutions and new installations.

(21) The conversion unit of mixtures of a biological origin obtained with the transformation method of the present invention is also an object of the invention, as is also a HDO/ISO process carried out using said conversion unit of mixtures of a biological origin.

(22) A further object of the invention also relates to a HDO/ISO process for the production of a hydrocarbon fraction, wherein said hydrocarbon fraction can be used as a fuel, or fuel component, starting from a mixture of a biological origin containing fatty acid esters, and possibly containing free fatty acids, which comprises the following steps:

(23) (1) hydrodeoxygenation of the mixture of a biological origin;

(24) (2) separation of the mixture resulting from step (1) into a hydrocarbon fraction and a gaseous mixture G comprising H.sub.2, CO.sub.2 and H.sub.2S,

(25) (3) hydroisomerization of the hydrocarbon fraction obtained in step (2),

(26) (4) separation of the gaseous mixture G into a stream of hydrogen and a gaseous mixture of CO.sub.2 and H.sub.2S,

(27) (5) separation of the gaseous mixture of CO.sub.2 and H.sub.2S obtained in step (4) into a stream of H.sub.2S and a stream of CO.sub.2,

(28) (6) feeding the stream of H.sub.2S obtained in step (5) to the hydrodeoxygenation step.

(29) The hydrogen obtained in step (4) is also re-fed to the hydrodeoxygenation step. The re-feeding of the H.sub.2S to the hydroisomerization step allows the catalyst of said step to be kept in its sulfided form, and therefore active, without the necessity of having to add further sulfiding agents, or in any case adding them in a reduced quantity.

(30) The revamping method, object of the invention, the HDO/ISO unit obtained using the revamping method of the present invention, the HDO/ISO process using said HDO/ISO unit, and the particular process comprising steps (1)-(6) indicated above, allow the production of diesel having excellent properties (high cetane index, optimum cold properties, high calorific value) and a stream of gas rich in propane which, after purification with amines, is in line with the specifications of commercial LPG obtained with the known methods, at the same time maintaining its biocomponent nature. A kerosene fraction and a naphtha fraction are also obtained, wherein said naphtha fraction can be used as such as gasoline base, by upgrading its bio portions thanks to integration in the gasoline pool of refineries, or sent to reforming, thus contributing to the synthesis of hydrogen to be used in the HDO/ISO process.