KR20110008140A - Incinerator for boil-off gas - Google Patents

Abstract

PURPOSE: An evaporative gas incinerator is provided to increase service life and to reduce the total temperature of the products of combustion without the use of a stirring device. CONSTITUTION: An evaporative gas incinerator comprises a combustion part(82). Evaporative gas(G) is incinerated to form combustion products where air exists. Dilution air is provided to the combustion part to cool the combustion products. One part of the dilution air flows across an incinerator in order to shatter the combustion products into pieces.

Description

Evaporative Gas Incinerator {INCINERATOR FOR BOIL-OFF GAS}

The present invention relates to incinerators, in particular incinerators for treating boil-off gas in ships carrying liquefied natural gas (LNG) in the sea, commonly known as LNG carriers. However, the incinerator of the present invention is not limited to the treatment of boil-off gas in such LNG carriers.

European Patent Application No. 05 802 431.6, which continues at the same time as the present application, shows that in the incinerator, in the presence of combustion air in the incinerator, the evaporation gas is blown into the proximal unit of the combustion section where the evaporation gas is incinerated, and the dilution air is mixed with the combustion product. And an incinerator for cooling the combustion products. Dilution air serves primarily to cool the combustion product such that the temperature of the combustion product is below the spontaneous ignition temperature of the gas.

Although blowing of dilution air is effective at lowering the average temperature of the combustion product to an acceptable level, a portion of the combustion product is typically higher than the target maximum temperature and the temperature of the other portion is low. In particular, the combustion products tend to form flows having relatively hot cores, ie cores that are above the average temperature of the flow and potentially above the spontaneous ignition temperature of the gas. If this structure is not comminuted, the temperature of a portion of the combustion product exiting the incinerator will exceed the spontaneous ignition temperature of the gas and can have dangerous consequences.

Previous attempts to crush combustion streams have had to provide some sort of mixing device in the incinerator. In one such known apparatus, the combustion section is covered with a perforated metal dome that spreads the combustion product before the combustion product is mixed with the dilution air. Another known apparatus has a metal disk that directs the combustion products to the side of the incinerator where the combustion products are mixed with dilution air. Since these mixing devices are directly exposed to hot combustion products, their service life is limited by high temperature oxidation.

It is an object of the present invention to lower the temperature of the entire combustion product to an acceptable level without using a mixing device exposed to the combustion product.

According to the present invention, the evaporation gas is incinerated in the presence of air to form a combustion product stream, and the combustion unit is supplied with dilution air to cool the combustion product, the evaporation gas in the LNG carrier In an incinerator for treating, an incinerator is provided, characterized in that at least one fraction (D ^P ) of dilution air is blown across the incinerator to pulverize the stream of combustion product.

The invention is not particularly applied solely to incinerators of the type described above, but is also claimed in European Patent Application No. 05 802 431.6, which is also a concurrent application of the present application, the disclosures of which are incorporated herein by reference. Simultaneous continuation of the present application A feature of the incinerator of the European patent application is that dilution air passes over the combustion section between the combustion product stream and the wall of the combustion section in order to separate the combustion product from the first wall. Due to this feature, the hot combustion products and the dilution air are less mixed, while the hot combustion products are surrounded by the relatively cold dilution air layer. The streamlined structure is crushed by blowing the fraction of dilution air D ^P across the incinerator.

Combustion products flow in a substantially vertical direction and the fraction of dilution air D ^P is blown across the incinerator in a substantially horizontal direction.

The incinerator of the preferred embodiment comprises a plurality of nozzles disposed around the outside of the combustion product stream and directed such that the fraction of dilution air D ^P is blown across the incinerator. The nozzles may be arranged at different intervals around the combustion product stream, respectively. The furnace is a classification (D ^P) that may include a plenum chamber (plenum chamber), or similar device to be supplied to the nozzles, preferably diluted classification of air (D ^P) of the dilution air pressure, each The nozzle is formed to accelerate dilution air passing through the nozzle.

Preferably, the fraction of dilution air (D ^P ) is mixed with the combustion products in turbulent form, and the mixture becomes substantially uniform before the mixture is discharged from the incinerator and the maximum temperature of any part of the mixture is reduced to It is preferable not to reach or exceed the spontaneous ignition temperature.

The fraction of dilution air D ^Q may pass over the first wall to cool the first wall. When using such a device, the classification prior to the combustion section supplied to the first and on the outside of the first wall and a second wall, the first and second walls is a classification (D ^Q) of the dilution air combustion unit (D ^Q) It is preferable to form the first passage through which the passes. It is preferable that the fraction D ^Q of dilution air flows in the first passage in a direction opposite to the flow direction of the combustion product in the combustion section. The combustion section is spaced inward of the first wall of the combustion section and defines a second passage in communication with the first wall at or near the proximal end of the combustion section with the first wall and near the proximal or proximal end of the combustion section. From may include a flame block extending into the combustion unit.

The present invention extends to LNG carriers comprising incinerators of the type described above.

Other aspects of the present invention will become apparent from the following description, which is set forth for illustrative purposes only with reference to the accompanying drawings.

According to the present invention, the temperature of the entire combustion product can be lowered to an acceptable level without using a mixing device exposed to the combustion product.

1 is a vertical sectional view of an LNG carrier including a boil-off gas incinerator from a port beam.
FIG. 2 is a vertical sectional view of a known boil-off gas incinerator installed on the LNG carrier shown in FIG. 1, shown at an enlarged scale.
FIG. 3 is a vertical sectional view of another known boil-off gas incinerator installed on the LNG carrier shown in FIG. 1, shown at approximately the same scale as FIG.
4 is a vertical sectional view of an incinerator according to the invention, shown on a larger scale.
FIG. 5 is a schematic plan view of the incinerator of FIG. 4 illustrating the radial arrangement of the dilution air nozzle. FIG.
FIG. 6 is an exemplary temperature profile across diameter d in XX of FIG. 4.
FIG. 7 is an exemplary temperature profile across diameter d in YY of FIG. 4.

Referring first to FIG. 1, FIG. 1 shows an LNG carrier, generally indicated at 10. The carrier ship 10 carries the LNG cargo 12 stored in the adiabatic tank. The carrier ship 10 is driven by the propulsion system 16. The propulsion system 16 includes a diesel engine, but may also be a dual fuel (gas / oil) system, a dual fuel (gas / oil) diesel-electric system or a dual fuel (gas / oil) steam-power system.

Although the tank 14 is insulated, some LNG gas is inevitably evaporated during the voyage, and thus the carrier ship 10 is provided with a liquefaction facility 18 for reliquefying the generated boil-off gas connected to the tank 14. In case the liquefaction facility 18 does not meet the demand or the liquefaction facility fails, the carrier 10 is provided with means for treating the evaporation gas in the form of an incinerator 20. (To prevent completeness and uncertainty, carriers not equipped with a liquefaction facility require an incinerator to treat excess evaporative gas when a typical gas consuming device such as a dual fuel engine consumes only a portion of the evaporative gas. For simplicity, the incinerator 20 is shown as being adjacent to the stern of the vessel 10, although one of ordinary skill in the art will appreciate that the incinerator is in the chimney assembly of the vessel. It will be appreciated that it can be integrated or deployed elsewhere.

The incinerator 20 is connected to the tank 14 via a gas line 22. The control system 24 is connected to the propulsion system 16 and the liquefaction system 18 at portions indicated by 26 and 28, respectively, and to the incinerator 20 at the portions indicated by 30. If the liquefaction system 18 (or a conventional gas consuming device) fails or only a portion of the evaporating gas is consumed, the gas line 22 is opened and the incinerator 20 operates to burn the evaporating gas. Such evaporative gas treatment means may continue to operate until necessary, until repair is made, or as necessary.

To date, various incinerators for treating boil-off gas in LNG carriers have been proposed, an example of which is shown in FIG. 2, and in FIG. 2 an arrow indicating the flow of gas, air and combustion products. The known incinerator 40 shown in FIG. 2 comprises a combustion section 42 which is generally cylindrical in the outer shell 44 and extends in the vertical direction. Each combustion part 42 and the outer shell 44 are made of steel, and the refractory bricks 46 are lined with the combustion part 42. Gas line 22 (FIG. 1) feeds evaporated gas G to gas inlet 48 of the proximal end (ie, bottom) of incinerator 40. The combustion air A is blown into the combustion section 42 by the combustion air fan 50, and the mixture of the boil-off gas G and the combustion air A is ignited (the ignition means is not shown in detail, but a conventional The technician will easily understand the means of ignition). Accordingly, the boil-off gas is incinerated at the portion indicated by 52, and the combustion product stream flows above the combustion section 42 and exits through the drilled dome 42a of the combustion section 42. It will be appreciated that a large amount of heat is generated during the combustion process and the combustion product (C) is mixed with dilution air (D) to cool the combustion product (C). The dilution air fan 54 blows the dilution air D into the annular space between the combustion section 42 and the outer shell 44. The dilution air D rises to meet the combustion product C, and the puncturing dome 42a functions to mix the combustion product C and the dilution air D. Then, the mixture M produced by mixing the combustion product and the dilution air is moved to an outlet (not shown).

Another incinerator previously proposed as an incinerator for treating evaporative gas in LNG carriers is shown in FIG. 3. In FIG. 3 the flow of gas, air and combustion products is indicated by arrows. The incinerator 60 shown in FIG. 3 extends generally cylindrically and vertically in the outer shell 64 and includes a combustion section 62 made of steel. Gas line 22 (FIG. 1) feeds boil-off gas G to gas inlet 66 at the proximal end (ie, bottom) of incinerator 60. The air A is blown into the combustion section 62 by the fan 68, and the mixture of the boil-off gas G and the combustion air A is ignited (the ignition means is not described in detail, but fired by a person skilled in the art). Easy to understand means). Accordingly, the evaporated gas is incinerated at the portion indicated by 70, and the combustion product stream flows upward through the combustion section 62. In order to cool the combustion product C, some air A is supplied through the annular space between the combustion section 62 and the outer shell 64, and the air passing through the port in the combustion section 62 is diluted air. Function as. Since this air does not mix completely with the combustion product (C), the metal plate 72 directs the combustion product (C) outward to mix the combustion product (C) and the air (A) for mixing to the required degree. It extends across the path of (C). The mixture M of combustion product and dilution air is then moved to an outlet (not shown).

Both known devices of FIGS. 2 and 3 present a serious problem that the mixing devices (perforation dome 42a of FIG. 2 and cross plate 72 of FIG. 3) are exposed to the combustion product stream. Since these mixing devices are all made of steel, their service life is inevitably limited at the temperatures to which they are exposed.

The present invention overcomes this problem by not using a (physical) mixing device in the combustion product stream. This will be described with reference to FIG. 4 where the flows of gas, air and combustion products are indicated by arrows as in FIGS. 2 and 3. The incinerator 80 shown in FIG. 4 extends generally cylindrically and vertically in the outer shell 84 and includes a combustion section 82 made of steel. A generally cylindrical heat shield 86 stands from the proximal end (ie, bottom) of the burner 82. Accordingly, an outer annular passage 88 is formed between the combustion portion 82 and the outer shell 84, and an inner annular passage 90 is formed between the combustion portion 82 and the heat shield 86. The combustion part 82, the outer shell 84, and the heat shield 86 are arrange | positioned.

Gas line 22 (FIG. 1) feeds boil-off gas G to gas inlet 92 at the proximal end of combustion section 82. The combustion air A is blown into the combustion section 82 by the combustion air fan 94, and the mixture of the boil-off gas G and the combustion air A is ignited (the ignition means is not shown in detail, but usually The technician will understand the means of ignition easily). Accordingly, the boil-off gas is incinerated at the portion indicated by 96, and the combustion product stream flows upward through the combustion section.

At the distal end (ie, top) of the combustion section 82, there is a plenum chamber or similar device 98 for dilution air supplied by the dilution air fan 100 for pressurizing the dilution air. The dilution air is divided into two parts: the fraction D ^{P which} is blown across the combustion section 82 through the nozzle 102 and the fraction D ^Q which is directed downward through the outer annular passage 88.

The nozzle 102 is configured to accelerate the dilution air D ^P flowing through the nozzle to infiltrate the dilution air into the combustion product stream to crush the combustion product. This produces a turbulent mixture of the ductile product and dilution air, indicated by reference M. By slightly varying the spacing of the nozzles 102 along the combustion product stream, as can be seen from the relative offset of the double dashed arrows representing the jets respectively emitted from the two nozzles 102 shown in FIG. Gets worse.

As can be seen from FIG. 5, the four nozzles 102 of the present incinerator are arranged at right angles and each nozzle is directed in the radial direction. It should be understood that the number of nozzles may be more or less than this.

Referring again to FIG. 4, the fraction of dilution air (D ^Q ) descending through the outer annular passageway 88 first passes through the wall of the combustion section 82 while flowing in a manner opposite to the generally upwardly flowing combustion product (C). Cool. At the bottom of the combustion section 82, this dilution air D ^Q flows upward and flows into the inner annular passageway 90, diluting and burning the combustion product C from where it is fed to the combustion section 82. Cool. For completeness, the air in the inner and outer passages 90 and 88 provides a thermal insulation layer around the combustion section 82 to limit heat transfer radially outward from the combustion section and near the bottom end of the incinerator. Horizontal thermal barriers, such as fractional beds, may be provided.

As can be seen by measuring the temperature profile across the combustion section 82, the dilution air D ^Q supplied to the combustion section 82 is incompletely mixed with the combustion product C. 6 shows an example temperature profile in cross section XX. The average temperature of the flow 110 (ie, the average value across the cross section XX) is below the spontaneous ignition temperature T ^A of the boil off gas. However, the temperature of the portion 112 of the flow 110 (outer portion of the flow) is substantially below T ^A , while the temperature of the other portion 114 is above T ^A. Those skilled in the art will appreciate that a flow 110 containing such a hot spot is dangerous if discharged near air vapor gas exiting the cargo tank of an LNG carrier.

In the present invention, this problem is overcome by the cross jet of dilution air D ^P acting on the combustion product C flow. This can be seen by comparing the upstream temperature profile of the jet shown in FIG. 6 with the downstream temperature profile in cross section YY shown in FIG. 7. From FIG. 7, after the jet of dilution air D ^P has penetrated the combustion product stream, the temperature profile of the resulting flow 120 across diameter d is substantially uniform, and the maximum local temperature is completely below T ^A. Becomes clear. Thus, there is no risk that the flow 120 is discharged in the vicinity of the air boil-off gas discharged from the cargo tank of the LNG carrier.

While other devices are possible, Applicants have found that it is effective to pressurize the dilution air up to about 20 mbar (typically 12-14 mbar). In addition, in dilution air is about 55% DP and 42% DQ and the remainder is bleed air for the flange.

It will be apparent to those skilled in the art that the device disclosed herein may be modified and may be applied to other applications than those disclosed herein.

Claims (14)

In an incinerator for treating boil-off gas in an LNG carrier, in which an evaporation gas is incinerated in the presence of air to form a combustion product stream and a dilution air is supplied to cool the combustion product. An incinerator, wherein at least one fraction of dilution air (D ^P ) is blown across the incinerator in order to break it down. 2. The combustion unit according to claim 1, wherein the combustion unit has a first wall, and different dilution air D ^Q is introduced into the combustion unit between the combustion product stream and the wall to separate combustion products from the first wall. Incinerator 3. The incinerator of claim 2, wherein the combustion product stream flows in a substantially vertical direction and the fraction (D ^P ) of dilution air is blown across the incinerator in a substantially horizontal direction. The incinerator according to any one of the preceding claims, characterized in that it comprises a plurality of nozzles arranged around the outside of the combustion product stream and directed such that the fraction of dilution air (D ^P ) is blown across the incinerator. Incinerator. 5. Incinerator according to claim 4, wherein the nozzles are arranged at different intervals around the combustion product stream. 4 according to any one of claims 5, wherein the furnace is a furnace comprising a plenum chamber, or similar device, which is supplied to the classification of the dilution air ^(P D) nozzle. 7. Incinerator according to any one of claims 4 to 6, wherein the fraction of dilution air (D ^P ) is pressurized and each nozzle is configured to accelerate the dilution air passing through the nozzle. The incinerator according to any one of the preceding claims, wherein the fraction of dilution air (D ^P ) is mixed with the combustion products in turbulent form and the temperature of the mixture is substantially uniform before the mixture is discharged from the incinerator. . 9. The incinerator of claim 8, wherein the maximum temperature of any portion of the mixture does not reach or exceed the autoignition temperature of the evaporating gas. 10. The incinerator according to any one of claims 2 to 9, wherein the fraction of dilution air (D ^Q ) cools the first wall as it passes over the first wall. The burner of claim 10, wherein the burner has a second wall on the outside of the first wall, the first wall and the second wall of the burner (D ^Q ) before the jet of dilution air (D ^Q ) is supplied to the burner. An incinerator, characterized in that to form a first passage through which. 12. The incinerator of claim 11, wherein the fraction D ^Q of dilution air flows in the first passage in a direction opposite to the flow direction of the combustion product in the combustion section. 13. A burner according to claim 11 or 12, wherein the combustion section is spaced inward of the first wall of the combustion section to define a second passageway communicating with the first wall at or near the proximal end of the combustion section with the first wall. And a flame blocker extending into the combustion section from the proximal end or near the proximal end of the burner. An LNG carrier comprising an incinerator according to any one of the preceding claims.

Images