Rapid sewage discharge structure of thin film type cargo containment system

Abstract

A rapid sewage discharge structure of a thin film type cargo containment system is characterized in that grids are arranged below insulating plates in corner areas at the periphery of the bottom of a cargo hold, and sewage discharge channels are arranged below the grids. When any cabin surface in the cabin leaks, flowing water flows to the bottom surface along the cabin wall and then can quickly permeate into the discharge channel through the grating. Sewage collected in the discharge channel enters the liquid collecting well through the blow-off pipe and then is sucked into the pipeline through the blow-off pump to be rapidly discharged, so that the problem of water accumulation at the bottom of the cargo hold is avoided, and meanwhile, the drainage rate in the cargo hold is increased. A secondary nitrogen main pipe connected with a nitrogen generator is connected into the discharge channel and is connected with an annular secondary nitrogen branch pipe in the discharge channel, the secondary nitrogen branch pipe is provided with a plurality of openings, after nitrogen is introduced into the pipe, residual sewage can be purged in the discharge channel in all aspects, and due to the fact that the pressure in the cabin is positive, the secondary nitrogen can be discharged out of the discharge channel. Therefore, the sewage in the discharge channel is accelerated to flow into the liquid collecting well. The problem of water accumulation at the bottom of the cargo hold is avoided, and meanwhile the water drainage rate in the hold is increased.

Description

Technical Field

[0001] This invention belongs to the field of design and construction of MARKⅢ membrane-type liquid cargo containment systems for marine vessels, specifically relating to a rapid sewage discharge structure for a membrane-type containment system. Background Technology

[0002] The MARK III membrane-type cargo containment system, primarily designed by the French company GTT, is a system designed for the storage and transportation of liquefied natural gas (LNG) and is widely used in LNG carriers. Its structure can be broadly divided into a primary shielding layer made of stainless steel corrugated sheets, a secondary shielding layer to prevent cargo leakage, a primary insulation layer composed of reinforced polyurethane foam, and a secondary insulation layer. The primary and secondary layers are bonded to the bottom of the cargo hold using epoxy resin.

[0003] To ensure the safety of itself and the liquid cargo, nitrogen needs to be continuously injected into the main space formed by the main and secondary shield walls, and the secondary space formed by the secondary shield wall and the hull bottom, after the vessel begins operation. This is to promptly purge any leaking natural gas from the main and secondary spaces and maintain positive pressure from the outside in. Additionally, considering that the hull may crack due to fatigue, leading to leaks or condensation in the isolation spaces, one or two drain holes are installed at the bottom of the stern of each cargo hold. Furthermore, continuous resin strips or spaced flat steel bars are installed on the bottom of the cargo holds to prevent and guide sewage flow to the drain holes.

[0004] The insulation layer of a thin-film cargo containment system is divided into planar area insulation plates, bifacial corner insulation plates, and trifacial insulation plates, depending on their location. As their names suggest, each insulation plate is located in the planar area of ​​each tank deck, the intersection area of ​​two tank decks, and the intersection area of ​​three tank decks, respectively. A bifacial corner insulation plate is adhered around the bottom perimeter of the liquid cargo tank, such as... Figure 1 As shown, continuous resin strips or spaced flat steel bars are installed between the insulating plates at the two corners of the bottom surface and the insulating plates at the planar boundaries, forming a rectangular ring structure around the bottom of the cargo hold. A collection well is installed below the bottom of the isolated compartment. Drainage holes are connected to the collection well via sewage pipes, and the wastewater in the collection well is then discharged by a vacuum pump. The collection well is also connected to a nitrogen pipeline from the isolated compartment; the nitrogen purged from the secondary space enters the secondary insulating space in the reverse direction along the aforementioned sewage pipe.

[0005] While the current design can achieve the goals of supplying nitrogen to the secondary insulation space and draining wastewater, several issues arise. When cracks in the cargo hold's inner shell expand and enlarge, a large volume of wastewater floods into the secondary space. This wastewater, flowing through the gaps between the resin strips at the bottom of the insulation board, fills the drainage pipes, preventing the replenishment of nitrogen into the secondary insulation space. Furthermore, when there is leakage or a small amount of condensate forming in the secondary space, the nitrogen in the drainage pipes flows in the opposite direction to the water, failing to quickly purge wastewater from the drain holes. If wastewater cannot be drained promptly, moisture will remain in the secondary space, leading to icing. The expansion force of the ice layer can cause deformation and cracking of the insulation layer, thus affecting the safety of the entire cargo containment system. Simultaneously, the ice layer can damage the thermal insulation properties of the insulation layer, making the temperature inside the membrane compartment more susceptible to external temperature fluctuations. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a structure and method for rapid wastewater discharge from a membrane-type enclosure system, aiming to improve the wastewater drainage rate of the membrane-type enclosure system and enhance the safety of the cargo enclosure system. The technical solution adopted is as follows:

[0007] A rapid wastewater discharge structure for a membrane-type cargo containment system includes an isolation chamber at one end of the cargo tank. A sunken discharge channel is located at the bottom of the cargo tank and along its circumference. A grating is laid above the discharge channel, and the grating is located in the non-adhesive area under the two corner insulating plates. A ring of annular retaining irons matching the shape of the grating is welded below the floor of the cargo tank in the grating installation area. After the grating is aligned, it is welded and fixed. After fixing, the top surface of the grating is on the same horizontal plane as the floor inside the ship.

[0008] The bottom of the isolation compartment is equipped with a liquid collection well, which is adjacent to the discharge channel. A sewage outlet is located at the bottom of the discharge channel in the stern direction. The sewage outlet is connected to a sewage pipe, which is connected to the liquid collection well. The sewage pump suction line extends into the liquid collection well.

[0009] The isolation chamber is equipped with a secondary nitrogen main pipe. Inside the venting channel, along the circumference of the venting channel, there are secondary nitrogen branch pipes. The secondary nitrogen main pipe is connected to the venting channel from the side of the liquid collection well and is connected to the secondary nitrogen branch pipes. Multiple exhaust holes are opened on the secondary nitrogen branch pipes.

[0010] The inner surface of the liquid cargo tank is coated with resin strips. For the insulating panels in the flat areas, the resin strips are applied longitudinally on the upper and lower inclined surfaces of the liquid cargo tank, while the resin strips are applied transversely on the remaining tank surfaces. The liquid cargo tank has an octagonal structure, with its upper left, upper right, lower left, and lower right inclined relative to the horizontal plane, forming upper and lower inclined surfaces.

[0011] Furthermore, in the aforementioned rapid sewage discharge structure of a membrane-type cargo containment system, the length W of the grille is less than the distance W1 between the two pads of the two-sided corner insulating plate, satisfying W1 = W + 60~80 mm.

[0012] Furthermore, in the aforementioned membrane-type cargo containment system with rapid wastewater discharge structure, the thickness and material of the grille are the same as those of the floor inside the liquid cargo tank.

[0013] Furthermore, in the aforementioned membrane-type cargo containment system for rapid wastewater discharge, the secondary nitrogen branch pipe is fixed to the discharge channel via a nitrogen branch pipe support located at the bottom of the liquid cargo tank.

[0014] Furthermore, in the aforementioned membrane-type cargo containment system for rapid wastewater discharge, an inlet monitoring device is installed in the discharge channel, and the inlet monitoring device is connected to the drainage pump.

[0015] Furthermore, in the aforementioned rapid wastewater discharge structure of a membrane-type cargo containment system, the generator is connected to the nitrogen main pipe via a valve assembly.

[0016] Furthermore, in the aforementioned rapid sewage discharge structure of a membrane-type cargo containment system, the distance H from the edge of the grille to the center point of the nearest resin strip is 15~40mm.

[0017] To expedite wastewater discharge from the secondary cargo hold and prevent water accumulation on the bottom surface, this patent incorporates gratings beneath the insulating panels at the four corners of the cargo hold's bottom. Below these gratings are wastewater discharge channels. In the event of a leak on any surface within the hold, water flowing down the bulkhead to the bottom surface quickly seeps through the gratings into the discharge channels. Wastewater collected in these channels flows through a drain pipe into a collection well, and then is rapidly discharged via a drain pump connected to a waste pump line. This not only prevents water accumulation on the cargo hold bottom but also significantly accelerates the drainage rate within the hold.

[0018] In addition to addressing the issue of rapid drainage within the chamber, it was also necessary to accelerate the discharge of residual sewage in the venting channel, as incomplete drainage could lead to icing. Therefore, the secondary nitrogen main pipe connected to the nitrogen generator was connected to the venting channel and then to the annular secondary nitrogen branch pipe within the venting channel. The secondary nitrogen branch pipe has multiple openings, allowing nitrogen to be introduced into the pipe, thus thoroughly purging residual sewage within the venting channel. Due to the positive pressure inside the chamber, this accelerates the flow of sewage from the venting channel into the collection well. Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating the arrangement of continuous resin strips or spaced flat steel bars in the bilge.

[0020] Figure 2 This is the overall layout diagram of the rapid wastewater discharge structure for a membrane-type cargo containment system;

[0021] Figure 3 yes Figure 2 Partial cross-sectional view at point AA;

[0022] Figure 4 yes Figure 3 Enlarged view of a section at point B in the middle;

[0023] Figure 5 This is a schematic diagram of the secondary space nitrogen system;

[0024] Figure 6 This is a schematic diagram of a horizontally coated resin strip and a grid.

[0025] Figure 7 This is a schematic diagram of a longitudinally coated resin strip;

[0026] Figure 8 This is a schematic diagram of the whole-tank resin coating method;

[0027] Among them, 1-liquid collection well, 2-discharge channel, 3-isolation chamber, 4-liquid cargo tank, 5-secondary nitrogen main pipe, 6-grating, 7-sewage pump suction line, 8-sewage pipe, 9-secondary nitrogen branch pipe, 10-sewage outlet, 11-water inlet monitoring device, 12-resin strip, 13-stop iron, 14-insulation board for two-sided corner area, 15-pad block, 16-valve group, 17-nitrogen generator, 18-bottom plate inside the liquid cargo tank, 19-nitrogen branch pipe support. Detailed Implementation

[0028] The invention will be further described with reference to the accompanying drawings.

[0029] like Figure 2 As shown, a rapid wastewater discharge structure for a membrane-type cargo containment system is described. Since water may flow around the walls of the liquid cargo tank, a sunken discharge channel is installed around the bottom perimeter of the tank. A grating for seepage is installed on the top surface of the discharge channel. The grating is installed in the non-adhesive area under the corner insulating plate, meaning the grating length W is less than the distance W1 between the two pads of the corner insulating plate, satisfying W1 = W + 60~80 mm. The distance H from the edge of the grating to the center point of the nearest resin strip is 15~40 mm. Figure 6 As shown. This method effectively guides sewage into the discharge channel without affecting the fixation of the dihedral insulation plate. Figure 4 As shown, beneath the floor of the cargo tank in the grating installation area, a ring-shaped retainer matching the shape of the grating is welded to support it. The grating thickness and material are the same as the inner bottom plate. After alignment, the grating is welded and fixed, with its top surface flush with the bottom surface of the hull.

[0030] like Figure 2As shown, a collection well is installed in an isolated compartment adjacent to the stern of the cargo tank. The collection well is adjacent to the venting channel, and a sludge outlet is located at the bottom of the venting channel in the stern direction. A sludge pipe connected to the sludge outlet leads into the collection well, which is deeper than the venting channel. A sludge pump suction line connected to a sludge pump is also installed in the collection well. When there is leakage or condensation in the tank, the liquid flows down the tank wall to the bottom, passes through the grates, and enters the venting channel. Due to the ship's stern tilt during operation, the water in the venting channel flows towards the stern, collects at the sludge outlet, and flows into the collection well through the sludge pipe. The sludge is then discharged from the collection well by the sludge pump.

[0031] Meanwhile, to accelerate the drainage rate and maintain dryness within the venting channel, and to ensure a stable nitrogen input to the secondary space even with large-scale drainage, a secondary nitrogen main pipe is connected from the sump to the venting channel within the isolated compartment. This main pipe is then connected to a ring-shaped secondary nitrogen branch pipe within the venting channel. Multiple vent holes are located along the secondary nitrogen branch pipe, which is fixed to the venting channel by a nitrogen branch pipe support beneath the cargo tank. Additionally, a water ingress monitoring device is installed within the venting channel to monitor water ingress. If the warning water level is reached, the drainage pump power is increased to ensure the liquid level in the venting channel does not reach the nitrogen branch pipe. Figure 5 As shown, during ship operation, nitrogen generated by the nitrogen generator enters the main nitrogen pipe through a valve assembly, and then flows to each cargo tank. Taking a single cargo tank as an example, before entering the cargo tank, the main nitrogen pipe branches into a secondary nitrogen pipe and a main nitrogen pipe. For the secondary space, nitrogen enters the tank through the annular nitrogen branch pipe exhaust port in the venting channel after passing through the secondary nitrogen pipe. Due to the influx of nitrogen into the secondary space, a positive pressure is created. When there is liquid in the venting channel, the liquid quickly flows towards the drain pipe under the purging of the secondary nitrogen branch pipe exhaust port, thus preventing liquid residue in the venting channel. The annular nitrogen branch pipe also facilitates the diffusion of nitrogen in the secondary space, accelerates the gas replacement rate in the secondary space, and improves the safety of the cargo containment system.

[0032] While accelerating the drainage rate, it is also necessary to improve the liquid flow at sewage leakage points or condensation points, allowing it to quickly flow to the cargo hold floor and preventing water accumulation in the gaps between the resin strips under the insulation board. Therefore, the resin coating method under the insulation board in each area needs to be defined. For the bifacial and planar insulation boards, there are typically two coating methods, such as... Figure 6 The image shows a horizontally coated resin strip. Figure 7 Resin strips are applied longitudinally. For example... Figure 8As shown, due to the ship's stern-listing state during navigation, to ensure unobstructed water flow channels between the resin strips and to ensure the overall water flow direction is downward and towards the stern, according to the typical insulation arrangement scheme of the MARK-type cargo containment system, for the planar area insulation panels, only the upper and lower slopes are required to use longitudinal resin strip coating, while the remaining tank surfaces use transverse resin strip coating. For the two-sided corner insulation panels, only the two-sided corner insulation panels where the upper and lower slopes intersect with the fore and aft tank surfaces, and the two-sided corner insulation panels where the port and starboard tank surfaces intersect with the fore and aft tank surfaces, use longitudinal resin strip coating; the other two-sided corner insulation panels use transverse resin strip coating. When water flows on any tank surface, the liquid will quickly drain along the gaps in the resin strips on the tank walls to the bottom, without any transverse resin strips obstructing the drainage channels. After reaching the bottom, the liquid immediately seeps into the drainage channels through the grille, preventing overflow into the inner area of ​​the bottom surface and ensuring that no water accumulates under the insulation panels on each tank surface.

Claims

1. A rapid wastewater discharge structure for a membrane-type cargo containment system, characterized in that, An isolation compartment is provided at one end of the liquid cargo tank. A sunken discharge channel is provided at the bottom of the liquid cargo tank and along the circumference of the liquid cargo tank. The discharge channel is connected to the secondary space. A grid is laid on the top of the discharge channel. The grid is located in the non-adhesive area under the two corner insulation plates. Under the floor of the liquid cargo tank in the grid installation area, a ring of iron blocks matching the shape of the grid is welded. After the grid is aligned, it is welded and fixed. After fixing, the top surface of the grid is on the same horizontal plane as the floor inside the ship. The bottom of the isolation compartment is equipped with a liquid collection well, which is adjacent to the discharge channel. A sewage outlet is located at the bottom of the discharge channel in the stern direction. The sewage outlet is connected to a sewage pipe, which is connected to the liquid collection well. The sewage pump suction line extends into the liquid collection well. The isolation chamber is equipped with a secondary nitrogen main pipe. Inside the venting channel, along the circumference of the venting channel, there are secondary nitrogen branch pipes. The secondary nitrogen main pipe is connected to the venting channel from the side of the liquid collection well and is connected to the secondary nitrogen branch pipes. Multiple exhaust holes are opened on the secondary nitrogen branch pipes.

2. The rapid wastewater discharge structure for a membrane-type cargo containment system according to claim 1, characterized in that, The length W of the grid is less than the distance W1 between the two pads of the two-sided corner insulation plate, satisfying W1=W+60~80 mm.

3. The rapid wastewater discharge structure for a membrane-type cargo containment system according to claim 1, characterized in that, The thickness and material of the grille are the same as those of the floor inside the liquid cargo tank.

4. The rapid wastewater discharge structure for a membrane-type cargo containment system according to claim 1, characterized in that, The secondary nitrogen branch pipe is fixed to the venting channel through a nitrogen branch pipe bracket at the bottom of the liquid cargo tank.

5. The rapid wastewater discharge structure for a membrane-type cargo containment system according to claim 1, characterized in that, The discharge channel is equipped with a water inlet monitoring device, which is connected to the drainage pump.

6. The rapid wastewater discharge structure for a membrane-type cargo containment system according to claim 1, characterized in that, The nitrogen generator is connected to the main nitrogen pipeline via a valve assembly.

7. The rapid wastewater discharge structure for a membrane-type cargo containment system according to claim 1, characterized in that, The distance H from the edge of the grille to the center point of the nearest resin strip is 15~40mm.

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