RU240211U1 - Inlet pipe for feeding synthesis gas into the heat exchanger - Google Patents

Abstract

This utility model pertains to heat engineering, specifically to heat exchange devices, such as those used in gas and oil refining processes. An inlet tube for feeding synthesis gas into a heat exchanger comprises a first end section designed for attachment to a tube sheet and a second end section designed to be positioned within the heat exchange tube to form an annular gap. The second end section is equipped with an ejector configured to create a low-pressure region within the heat exchange tube. The technical result consists of reducing the heat load.

Description

The field of technology to which the utility model belongs

The utility model relates to the field of heat engineering, in particular to means for implementing heat exchange, for example, in gas and oil refining processes, including for the utilization of synthesis gas in the production of ammonia.

State of the art

A heat exchange apparatus known from the prior art comprises a refrigerant chamber provided with an inlet and outlet pipe for the refrigerant, a coolant chamber having an inlet chamber with an inlet pipe for the coolant and an outlet chamber with an outlet pipe for the coolant, a tube sheet with openings separating said refrigerant and coolant chambers, heat exchange tubes installed in the openings of said tube sheet, each of which is provided with an inlet pipe for the coolant, the first end of which is fixed in a tube sheet, and the second is located inside the corresponding heat exchange tube to form an annular gap, said tube sheet separating said inlet and outlet chambers for the coolant (RU Patent No. 2599889, published on 20.10.2016). This known means requires the manufacture of long inlet pipes for the coolant with high precision and does not ensure sufficient thermal efficiency.

The essence of the utility model

The utility model solves the problem of creating heat exchange technologies with increased heat transfer efficiency.

The achieved technical result consists of a decrease in the heating temperature of the tube sheet and a reduction in the required length of the inlet tubes, as well as the diameter of the heat exchange tubes.

The said technical result is achieved in that the inlet tube for feeding synthesis gas into the heat exchange apparatus is made of stainless steel and contains a first end section intended for fastening in a tube sheet, and a second end section for placement inside the heat exchange tube to form an annular gap, characterized in that the said second end section is equipped with an ejector designed with the possibility of creating a List of figures of the drawings

Fig. 1 shows a heat exchanger with U-shaped heat exchange tubes.

Fig. 2 shows a heat exchanger with straight heat exchange tubes.

Fig. 3 shows a bayonet diagram of the heat exchange and inlet tubes.

Fig. 4 shows a variant of the ejector design.

Implementation of a utility model

Heat exchange equipment operates under harsh conditions (high temperatures, large temperature differences, high pressure drops, aggressive environments, etc.). Improving the efficiency of heat exchange processes under such conditions has always been a major focus.

For example, in industrial ammonia production, an exothermic reaction between hydrogen and nitrogen occurs, producing ammonia. Ammonia synthesis occurs in a reactor at high pressure and elevated temperature while nitrogen and hydrogen pass through a catalyst bed. This reactor is called an ammonia synthesis column. The heat released during the exothermic reaction in the synthesis column is often recovered by generating steam in a syngas waste heat boiler. The syngas waste heat boiler is a heat exchanger in which hot gas from the ammonia synthesis column is cooled through indirect heat exchange with boiling water. The syngas waste heat boiler operates under challenging conditions, which in many respects require a specialized design. The most stringent requirements are placed on the connections of the heat exchange tubes, particularly their inlet section, and the tube sheet.

Syngas for ammonia production is typically under pressure of 120-220 bar. Boiling water is typically under low (5-15 bar), medium (30-50 bar), or high pressure (90-130 bar). The walls separating the syngas and boiling water must be designed to withstand the greatest pressure difference between the two media. In shell-and-tube heat exchangers, this typically necessitates the use of very thick tube sheets, typically 300-450 mm thick. Syngas for ammonia production can be at temperatures ranging from 380°C to 500°C at the inlet of the waste heat boiler and at temperatures up to 380°C at the outlet. Boiling water can be at temperatures ranging from 150°C to 330°C, depending on the steam pressure.

Syngas waste heat boilers are often designed as U-tube heat exchangers with very thick tube sheets. The thick tube sheet of the heat exchanger results in a metal temperature close to the gas temperature in the tubes passing through it. With U-tubes, the inlet portion of the heat exchanger tube will have a high temperature, while the outlet portion will have a lower temperature. Therefore, high temperature loads can be dangerous if the temperature difference between the inlet and outlet gas is too great.

The use of bayonet tubes (also known as Field tubes) in heat exchange equipment reduces superheating and minimizes thermal stress in tube sheets caused by temperature gradients. The principle of the bayonet design is that when a hot medium enters through the central tube, the cooled flow exits through an annular gap between the central tube and the outer tube, preventing excessive heating of the tube sheet, which is subject to a pressure differential. This ensures a fairly uniform temperature background across the tube sheet.

The bayonet design used in the prototype reduces the thermal load on the tube sheet by diverting a portion of the hot flow into the annular gap and cooling this portion of the flow en route to the tube sheet. The returning flow in the annular gap is cooled through the outer wall and heated by the bayonet wall. However, the bayonet inlet tube in this design must be sufficiently long (up to 1500 mm beyond the tube sheet) to ensure sufficient cooling of the flow in the annular gap. The long length of the bayonet tubes, as well as the need to ensure a uniform annular gap over long distances, require the use of expensive cold-rolled heat exchange tubes with a high-quality internal surface. The overall dimensions of the equipment also increase.

The proposed solution is based on changing the direction of coolant flow in the annular gap between the bayonet-type inlet tube and the heat exchanger tube. This change in flow direction is achieved by creating a low-pressure region at the end of the inlet tube, located inside the heat exchanger tube. This is achieved, for example, by installing a tip at the end of the bayonet-type inlet tube, which functions as an ejector. Slits are created in the tip in the ejection zone, through which coolant from the annular gap is drawn into the main flow flowing from the bayonet-type inlet tube into the heat exchanger tube. Thus, a portion of the already cooled coolant from the outlet chamber enters the annular gap.

The heat exchange apparatus contains a coolant chamber 1 equipped with an inlet 2 and outlet 3 branch pipes, a coolant chamber 4 having an inlet chamber 5 with an inlet branch pipe 6 of the coolant and an outlet chamber 7 with an outlet branch pipe 8 of the coolant.

The coolant chamber 1 and the heat carrier chamber 4 are separated by a tube sheet 9 with openings in which heat exchange tubes 11 are installed.

Each heat exchange tube 11 is provided with an inlet tube 12 of the coolant, one end of which is fixed in the tube sheet 13, and the second is located inside the corresponding heat exchange tube 11 with the formation of an annular gap 14.

The tube sheet 13 separates the inlet 5 and outlet 7 chambers of the coolant.

At the end of the inlet tubes 12 of the coolant, which is located inside the corresponding heat exchange tube 11, there is an ejector 15, which ensures the movement of the coolant in the annular gap 14 from the outlet chamber 7 in the same direction as the movement of the coolant in the inlet tube 12 itself. Such a flow input allows the use of short inlet tubes 12, which only slightly extend beyond the tube sheet 9 (within 100 mm), since cooled coolant is sucked in with a temperature approximately equal to the temperature of the coolant at the outlet of the heat exchange tubes 11. The difference between the diameters of the heat exchange tube 11 and the inlet tube 12 can also be reduced.

An embodiment of the ejector 15 is shown in Fig. 4. The region of reduced pressure in the coolant flow can be provided by the shape of the cross-section (nozzle) of the ejector 15 and the creation of slots 10 to enhance the effect.

Heat exchange tubes 11 can be made U-shaped, as shown in Fig. 1.

The heat exchange tubes 11 can be made straight, as shown in Fig. 2. In this case, an additional tube sheet 16 is installed in the coolant chamber 1, in which the upper ends of the heat exchange tubes 11 are fixed and which creates an additional coolant chamber 17.

Water or steam can be used as a coolant. Synthesis gas or process gas can be used as a heat transfer fluid.

At least part of the length of the inlet tubes 12 (for example, before entering the tube sheet) can be made thermally insulated (for example, by wrapping with thermal insulation material) or have double walls.

The device works as follows.

Tube sheet 9 is connected to refrigerant chamber 1 on one side and to coolant chamber 4 on the other, separating them. Tube sheet 9 is perforated with multiple holes, into which heat exchange tubes 11 are installed and welded, extending into refrigerant chamber 1.

Tube sheet 13 is located inside the coolant chamber 4 and is also perforated with holes. Inlet tubes 12, having a smaller outer diameter than the inner diameter of the heat exchange tubes 11, are attached to the holes of tube sheet 13, pass inside the heat exchange tubes 11 and form an annular gap 14. Tube sheet 13 separates the inlet chamber 5 and the outlet chamber 7 of the coolant, wherein the annular gap 14 and the other end of the heat exchange tube communicate with the outlet chamber 7 of the coolant.

A coolant, such as boiling water from a steam boiler, enters coolant chamber 1 through one or more inlet pipes 2 at a pressure of 3.5 MPa to 6.8 MPa and a flow rate of 0.7 t/h to 1.4 t/h. Heat exchange tubes 11, through which the coolant flows, provide heat to coolant chamber 1. The coolant (e.g., water, steam, or a mixture thereof) leaves coolant chamber 1 through one or more outlet pipes 3.

The inlet temperature of the refrigerant is in the range from 100°C to 350°C, preferably in the range from 250°C to 325°C, the outlet temperature of the refrigerant is in the range from 100°C to 350°C.

The coolant, for example hot synthesis gas from the ammonia synthesis column, enters the coolant inlet chamber 5 through the inlet pipe 6 under a pressure of 12 MPa to 26 MPa with a total flow rate of 240 t/h to 580 t/h. The coolant then passes through the openings of the tube sheet 13 into the inlet tubes 12 and further into the heat exchange tubes 11. After passing along the heat exchange tubes 11, the cooled coolant enters the outlet chamber 7. The coolant temperature at the inlet is in the range from 300°C to 500°C, at the outlet from 250°C to 295°C.

Due to the ejector 15 at the end of the inlet tubes 12 in the area of the coolant outlet from them, a reduced pressure is created inside the heat exchange tubes 11, which sucks in part of the cooled coolant from the outlet chamber 7 and ensures its movement along the annular gap 14 at a speed of 1 m/s to 9 m/s in the same direction as inside the inlet tubes 12. The excess cooled coolant is removed from the chamber 7 through one or more outlet pipes 8. The total length of the inlet tubes 12 can be from 400 mm to 900 mm, while the length after the tube sheet 13 can be from 50 mm to 500 mm.

The coolant drawn into the annular gap 14 from the outlet chamber 7 prevents the heating of the tube sheet 9 by the inlet coolant.

It is advisable to minimize the heat transfer between the inlet coolant passing through the inlet tubes 12 and the cooled coolant in the annular gap 14 by means of thermal insulation of the inlet tube 12.

Example of implementation of the utility model

Steam with a molecular weight of 18.02 kg/kmole and a density of 24.3 kg/ ^m3 is fed into chamber 1 through inlet pipe 2, at a flow rate of 1050 tons/hour, a temperature of 261°C and a pressure of 4.7 MPa. Synthesis gas is fed through inlet pipe 6 into chamber 5 of the coolant at a total flow rate of 390 tons/hour, a temperature of 422°C and a pressure of 17 MPa. The length of inlet tubes 12 is 200 mm after leaving the tube sheet, the total length is 600 mm. The inlet and outlet of heat exchange tubes 11 are connected by a common gas volume of outlet chamber 7 of the coolant. The material of the heat exchange and inlet tubes is stainless steel with a thermal conductivity of 16 W/(m K). The material of the tube sheet and tube sheet is low-alloy steel with a thermal conductivity of 48 W/(m⋅K). After reaching the operating mode, the maximum temperature of the tube sheet was 290°C.

To validate the utility model's advantages, a comparison was made with similar equipment performance indicators based on a prototype. The total length of the inlet tubes was 1900 mm, of which 1500 mm was the length of the section after the tube sheet. The maximum tube sheet temperature was 346°C with a comparable pressure drop.

Thanks to the utility model, tube sheet 9 comes into contact only with the cooled outgoing coolant. This minimizes the aforementioned problems of existing heat exchangers associated with hot inlet gas and the temperature difference between the tubes in a thick tube sheet. According to the utility model, tube sheet 13 for inlet tubes 12 is thin because this part is not under pressure and can be made of austenitic high-alloy steel because it does not interact with the coolant. The coolant outlet temperature does not exceed 290°C, compared to 340°C to 370°C in the prototype.

Claims (3)

1. An inlet tube for feeding synthesis gas into a heat exchange apparatus, made of stainless steel and comprising a first end section designed for fastening in a tube sheet, and a second end section for placement inside the heat exchange tube to form an annular gap, characterized in that said second end section is equipped with an ejector designed with the possibility of creating a region of reduced pressure inside said heat exchange tube. 2. An inlet tube according to paragraph 1, characterized in that the section intended for placement inside the heat exchange tube is made thermally insulated. 3. An inlet pipe according to paragraph 1, characterized in that the section intended for placement outside the heat exchange pipe is made thermally insulated.