Method and system for generating energy during the expansion of natural process gas

Abstract

Provided is a method for energy recuperation in the expansion of processed natural gas before the delivery of the latter to an acetylene production plant (H). The method includes delivery of heated processed natural gas to an expansion device and expansion of the processed natural gas in the expansion device to a pressure of 2 bar to 8 bar. The expansion device is a piston expansion machine which is operated by the expansion of the processed natural gas and which generates energy. Also provided is a plant for energy recuperation in the expansion of processed natural gas.

Claims

1. A method for energy recuperation in the expansion of processed natural gas during delivery to an acetylene production plant, comprising: a) delivering a processed natural gas from a processed natural gas supply line, wherein the processed natural gas has a temperature of ?10? C. to 50? C. and a pressure of 30 bar to 70 bar, to a first heating stage and heating the processed natural gas in the first heating stage to a temperature of 20? C. to 40? C., b) delivering the processed natural gas heated in the first heating stage to a second heating stage and heating the processed natural gas in the second heating stage to a temperature of 70? C. to 140? C., c1) delivering the processed natural gas heated in the second heating stage to a first expansion stage of a piston expansion machine, wherein the piston expansion machine operates by the expansion of the processed natural gas and which generates energy, and expanding the processed natural gas in the first expansion stage to a pressure of 15 bar to 25 bar, wherein the processed natural gas has a temperature of 15? C. to 25? C. after the expansion in the first expansion stage, c2) delivering the processed natural gas expanded in the first expansion stage to a third heating stage and heating the processed natural gas in the third heating stage to a temperature of 70? C. to 140? C., c3) delivering the processed natural gas heated in the third heating stage to a second expansion stage of the piston expansion machine and expanding the processed natural gas in the second expansion stage of the piston expansion machine to a pressure of 2 bar to 8 bar, wherein the processed natural gas has a temperature of 10? C. to 100? C. after the expansion in the second expansion stage, d) delivering the processed natural gas expanded in the second expansion stage of the piston expansion machine to a fourth heating stage and heating the processed natural gas in the fourth heating stage to a temperature of 40? C. to 100? C., wherein the processes natural gas has a pressure of 2 bar to 8 bar after the heating in the fourth heating stage, and e) delivering the processed natural gas having a pressure of 2 bar to 8 bar heated in the fourth heating stage to an acetylene production plant, wherein at least a portion of waste heat from the second heating stage and the third heating stage heats the processed natural gas in the fourth heating stage.

2. The method according to claim 1, wherein the piston expansion machine operates by the expansion of the processed natural gas driving a generator that generates electrical energy.

3. The method according to claim 1, wherein the heating of the processed natural gas in at least one stage selected from the group consisting of the first heating stage, the second heating stage, the third heating stage, and the fourth heating stage is performed in a plate heat exchanger.

4. The method according to claim 1, wherein the processed natural gas is heated to a temperature of 25? C. to 35? C. in the first heating stage.

5. The method according to claim 1, wherein the processed natural gas is heated to a temperature of 75? C. to 85? C. in the second heating stage.

6. The method according to claim 1, wherein the processed natural gas is expanded to a pressure of 19 bar to 22 bar in the first expansion stage.

7. The method according to claim 1, wherein the processed natural gas is expanded to a pressure of 4 bar to 6 bar in the second expansion stage.

8. The method according to claim 2, wherein at least a portion of waste heat from the generator heats the processed natural gas in the first heating stage.

9. The method according to claim 1, wherein the piston expansion machine is of at least two-stage design.

10. The method according to claim 1, wherein the piston expansion machine comprises a double-acting piston.

11. A plant for energy recuperation during the expansion of processed natural gas, comprising: a processed natural gas supply line, a first heating stage suitable for heating a processed natural gas, wherein the first heating stage is connected to the processed natural gas supply line via a feed line, a second heating stage suitable for heating the processed natural gas heated by the first heating stage, wherein the second heating stage is connected to the first heating stage via a line, a piston expansion machine suitable for expanding the processed natural gas heated by the second heating stage, and comprising a first expansion stage and a second expansion stage, wherein the piston expansion machine is connected to the second heating stage via a line, a third heating stage between the first expansion stage and the second expansion stage, wherein the third heating stage is connected to the first expansion stage via a line and is connected to the second expansion stage via a line, and a fourth heating stage suitable for heating the processed natural gas expanded in the second expansion stage of the piston expansion machine, wherein the fourth heating stage is connected to the second expansion stage via a line, wherein the second heating stage is connected to the fourth heating stage via a waste heat line, the third heating stage is connected to the fourth heating stage via a waste heat line, and the plant is connectable via one or more lines to an acetylene production plant.

12. The plant according to claim 11, wherein the piston expansion machine is connected to a generator configured for generating electrical energy.

13. The plant according to claim 11, wherein at least one stage selected from the group consisting of the first heating stage, the second heating stage, the third heating stage, and the fourth heating stage comprises a plate heat exchanger.

14. The plant according to claim 12, wherein: (i) the first heating stage is connected via a waste heat line to the generator, (ii) the second heating stage is connectable via a waste heat line to the acetylene production plant, (iii) the third heating stage is connectable via a waste heat line to the acetylene production plant, (iv) the fourth heating stage is connected via waste heat lines to the second heating stage and the third heating stage, or any combination of (i), (ii), (iii) and (iv).

15. The plant according to claim 11, wherein the piston expansion machine is of at least two-stage design.

16. The plant according to claim 11, wherein the piston expansion machine comprises a double-acting piston.

Description

(1) The single FIGURE shows a method diagram for energy recuperation in the expansion of processed natural gas.

(2) In the method according to the invention, the expansion of the processed natural gas P is carried out via a piston expansion machine E, instead of via a conventional regulating rail, the pressure expansion being utilized for performing in the piston expansion machine E mechanical work which in turn generates electrical current with the aid of a generator G.

(3) According to the First Law of Thermodynamics, the energy which is extracted from a gas during expansion in the form of mechanical work has to be returned to it in the form of heat in order to bring the gas to its initial temperature again after expansion.

(4) As may be gathered from the method diagram of FIG. 1, the processed natural gas P is delivered from a supply line, not illustrated in the FIGURE, with a pressure of up to 70 bar to the plant via a feed line Z, and, depending on the transport distance, the supply pressure may be reduced to 40 bar. The processed natural gas P has a temperature of between 0? C. and 25? C., depending on pressure, supply length and outside temperature.

(5) In a first heating stage WT1, the processed natural gas P is heated to a temperature in the range of 20? C. to 35? C. before it is delivered via a line L1 to a second heating stage WT2 and heated there further to a temperature in the range of 70? C. to 85? C.

(6) Plate heat exchangers are preferably used as heating stages WT1, WT2.

(7) The processed natural gas P, which is heated in the heating stages WT1, WT2 and is under a pressure of up to 70 bar, is then delivered via a line L2 to the piston expansion machine E. In the embodiment described, this is a piston engine of the company Spilling, the piston engines of which are predominantly known in the prior art as ships' diesel engines and which have not yet been used hitherto as piston expansion machines for large-scale use in plants for the production of acetylene.

(8) Via a pulsation damper, not illustrated in the FIGURE, the processed natural gas P is apportioned to six cylinders of a first expansion stage E1 of the Spilling piston engine, the cylinders being filled with the processed natural gas P via associated control slides. During expansion, the processed natural gas P drives a double-acting piston of the Spilling piston engine. The control slides and therefore the degree of filling of the cylinders are set by pressure regulation at the outlet of the first expansion stage E1.

(9) After the first expansion stage E1, the processed natural gas P emerges with a pressure of approximately 20 bar and a temperature of 15? C. to 25? C. via a pulsation damper and is delivered via a line L3 to a third heating stage WT3 where it is heated to a temperature in the range of between 70? C. and 85? C. before it is delivered via a line L4 to a second expansion stage E2.

(10) In the second expansion stage E2, in a similar way to the first expansion stage E1, the processed natural gas P is again apportioned to six cylinders via a pulsation damper. Here, too, associated control slides are set by pressure regulation at the outlet of the second expansion stage E2.

(11) The processed natural gas P emerges from the second expansion stage E2 with pressure 4 bar to 6 bar and a temperature of between 10? C. and 25? C. via a further pulsation damper and is delivered via a line L5 to a fourth heating stage WT4 where it is heated to 40? C. to 50? C. in order to relieve a heating stage (not illustrated in this FIGURE) which precedes the acetylene production H.

(12) The piston expansion machine E, that is to say, here, the Spilling piston engine, drives preferably at a maximum of 1000 U/min a generator G for current generation. The generated current may, for example, be utilized in the acetylene plant itself or be made available in other plants.

(13) The embodiment according to the invention is distinguished, furthermore, by an interconnected heat system which is described below.

(14) For the heating of the processed natural gas P extracted from the supply line via the feed line Z, in the first heating stage WT1 the waste heat of the generator G is utilized via a heat circuit A1 and the waste heat of the oil cooling system employed for cooling the Spilling piston engine E is utilized via a further heat circuit, not illustrated in the FIGURE.

(15) In the second heating stage WT2, condensate KP from the acetylene production plant H is utilized for heating the processed natural gas P via a waste heat line A2 and is supplemented, as required, by condensate KN from an internal network of the industrial plant. The condensate KP, KN has a temperature of 95? C. to 105? C. and is cooled in the second heating stage WT2.

(16) Likewise, in the third heating stage WT3, condensate KP with a temperature of 95? C. to 105? C. from the acetylene production plant H and, optionally, condensate KN from the internal network of the industrial plant are utilized via a waste heat line A3 in order to heat the processed natural gas P emerging from the first expansion stage E1 to 70? C. to 85? C.

(17) The heating, already described above, of the processed natural gas P expanded to 4 bar to 8 bar in the fourth heating stage WT4 takes place via waste heat lines A4, A5 with the condensate KP, KN, which has already been cooled in the heating stages WT2 and WT3. In these heating stages, the condensate KP, KN is cooled further and is subsequently delivered to the plant AW for utilizing the waste heat in the acetylene plant H. The condensate thus cooled is used for the condensation of low-pressure steam present in the plant, with the result that the use of cold, fully deionized water H.sub.2O can be reduced. The condensate reheated in the plant AW is delivered again to the condensate process via a waste heat line A7.

(18) By virtue of the embodiment according to the invention, the saving of fully deionized water H.sub.2O may amount to up to 370.000 t per year, while at the same time up to 8800 t per year of steam can be saved. In addition, in the acetylene production plant H, due to the higher temperature level of the processed natural gas in the line L6, 730 000 Nm.sup.3 per year of heating natural gas can be saved for the required heating of the processed natural gas to process temperature.

LIST OF REFERENCE SYMBOLS

(19) A1 Heat circuit

(20) A2, A3, A4, A5, A6, A7 Waste heat lines

(21) E Expansion device (piston expansion machine)

(22) E1 First expansion stage

(23) E2 Second expansion stage

(24) AW Plant for utilizing the waste heat

(25) G Generator

(26) H Acetylene production plant

(27) KN Condensate (network)

(28) KP Condensate (process)

(29) L1, L2, L3, L4, L5, L6 Lines

(30) P Processed natural gas

(31) S Power network

(32) WT1 First heating stage

(33) WT2 Second heating stage

(34) WT3 Third heating stage

(35) WT4 Fourth heating stage