Safe and environmentally friendly construction method for hydrogen-sulfide-containing soil

Abstract

Disclosed in the present invention is a safe and environmentally friendly construction method for hydrogen-sulfide-containing soil. The construction method comprises: arrangement of hydrogen sulfide detectors, wherein a plurality of hydrogen sulfide detectors and two monitoring hosts are arranged in a construction vessel, and the height of each hydrogen sulfide detector from the ground is 30-60 cm; optimization of a construction apparatus, wherein keels are welded around and above a mud hold of the vessel, a sealing film is used to seal the mud hold, with the sealed areas being an area of 15-20 meters on the side close to a bridge and an area of 10 meters at the rear section of the mud hold, a high-power axial-flow fan is arranged in the middle area, the interior of a mud door hole of a mud hold deck is filled with an expandable foaming agent, a cover plate is additionally mounted outside the mud door hole for blocking, and double-sided plow teeth are mounted at a wear-resistant block of a dredging head of the vessel; and construction, wherein hydrogen sulfide gas is dispersed before construction to ensure that the concentration value in a cabin is within a normal range, an external-circulation mode of a fan in an accommodation cabin of the vessel is turned off and an internal-circulation mode thereof is turned on during construction, and an explosion-proof axial-flow fan is used for ventilation to accelerate airflow. The present invention ensures the safe and efficient implementation of construction on hydrogen-sulfide-containing soil.

Description

Safe and environmentally friendly construction methods for soils containing hydrogen sulfide Technical Field

[0001] The present invention relates to the technical field of dredging engineering, and in particular to a safe and environmentally friendly construction method for soil containing hydrogen sulfide. Background Art

[0002] Hydrogen sulfide, an inorganic compound with the chemical formula H2S, is a flammable, explosive, highly toxic, and extremely corrosive gas. In waterway or dredging projects, the soil in the dredged area contains hydrogen sulfide gas. The gas may spread as the soil is disturbed during the dredging process. Improper protection can lead to immeasurable serious consequences, including casualties.

[0003] Existing dredging construction mainly uses trailing suction hopper vessels for construction. However, as the dredged soil becomes more and more complex, the existing equipment and construction technology cannot ensure safe production for soil containing hydrogen sulfide.

[0004] Summary of the Invention

[0005] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0006] Another object of the present invention is to provide a safe and environmentally friendly construction method for soil containing hydrogen sulfide, which addresses the defects of the existing technology, optimizes equipment and construction technology, and ensures that construction on soil containing hydrogen sulfide is carried out safely and efficiently.

[0007] In order to achieve these purposes and other advantages according to the present invention, the technical solutions of the present invention are as follows:

[0008] A safe and environmentally friendly construction method for soil containing hydrogen sulfide, comprising the following steps:

[0009] Step 1: Deploy hydrogen sulfide detectors: Deploy multiple hydrogen sulfide detectors and two monitoring hosts on the construction vessel, with each hydrogen sulfide detector at a height of 30 to 60 cm from the ground;

[0010] Step 2: Optimize construction equipment: Weld keels around and above the ship's mud tank, and use sealing membrane to seal the tank. The sealed area is 15-20 meters from the bridge and 10 meters behind the tank. High-power axial flow fans are installed in the middle area. The mud door holes on the mud tank deck are filled with expanding foam and covered with covers. Double-sided plow teeth are installed on the wear-resistant blocks of the ship's rake head.

[0011] Step 3. Construction: Before construction, the hydrogen sulfide gas in the cabin should be dispersed to ensure that the concentration of hydrogen sulfide in the cabin is within the normal range. During the construction process, the fan in the cabin of the ship will turn off the external circulation and turn on the internal circulation mode, and use explosion-proof axial flow fans for ventilation to accelerate air flow.

[0012] Preferably, in step 1, the detection alarm of the hydrogen sulfide detector is a secondary alarm mechanism, specifically including:

[0013] When the hydrogen sulfide detector detects a concentration greater than 10ppm and less than 20ppm, the detector will emit a buzzer and a yellow alarm light will sound. Construction workers must wear hydrogen sulfide respirators and continue construction. The ship's position must be adjusted according to the wind direction so that the bridge, respirators, and engine room monitoring room are all upwind.

[0014] When the hydrogen sulfide detector detects that the hydrogen sulfide concentration is greater than 20ppm, the detector will emit a buzzer and a red alarm light will sound. Construction workers will immediately wear respirators, stop construction immediately and move away from the construction area, and perform high-pressure water flushing and ventilation in the construction area.

[0015] Preferably, step three specifically includes:

[0016] When there is no wind, increase the speed by 2.5-3 knots to reduce the time hydrogen sulfide gas accumulates on the ship;

[0017] When the wind is blowing against you, continue construction as normal and pay close attention to the alarms of the multiple hydrogen sulfide detectors installed on the ship. Fans in the cabins of the ship should switch off external circulation and on to internal circulation mode, and explosion-proof axial flow fans should be kept running.

[0018] When the wind is crosswind, construction should be carried out in the inner channel area where the hydrogen sulfide gas is high; the explosion-proof axial flow fan should be kept on;

[0019] When the wind is favorable, the ship stops working.

[0020] Preferably, the quality inspection of step three and step two also includes: loading and ballast before construction: before construction, mud is injected into the ship's cabin, the highest overflow is adopted, the front loading cabin is closed, the high-pressure water flushing of the rake head is turned on at the wear-resistant block and one place inside the rake cavity, and the rake lip is raised to adjust the angle to separate the rake lip from the mud surface.

[0021] Preferably, step one further includes: equipping each construction worker with a portable hydrogen sulfide gas detector, when the concentration of hydrogen sulfide in the air is greater than 10ppm, the detector emits a buzzer alarm, and when the concentration of hydrogen sulfide in the air is greater than 15ppm, the detector emits a buzzer alarm and a red alarm light flashes.

[0022] Preferably, step one further comprises: each ship at the construction site is equipped with two four-in-one gas detectors for monitoring hydrogen sulfide gas and other toxic gases in the air.

[0023] Preferably, step 2 further includes: equipping each room in the ship's living quarters with a high-power cabinet fan; placing a 3000w high-power explosion-proof axial flow fan in the main engine room, pump room and repair room; and equipping the living quarters, pump room, engine room monitoring room and bridge with hydrogen sulfide breathing protective devices and emergency breathing apparatus that meet the needs.

[0024] Preferably, step three further comprises: during the mud throwing process, the vessel keeps throwing mud against the wind or across the wind.

[0025] Preferably, in step one, 30 hydrogen sulfide detectors are installed, all of which are fixed with steel frames, and there are 2 monitoring hosts, with specific installation locations as follows: 21 in the engine room, 9 in the cabin and the bridge, and the 21 hydrogen sulfide detectors in the engine room are connected in parallel with a 32-channel monitoring host, and the 32-channel monitoring host is placed in the engine room monitoring room, and the 9 hydrogen sulfide detectors installed in the cabin and the bridge are connected in parallel with a 16-channel monitoring host, and the 16-channel monitoring host is placed on the bridge.

[0026] Preferably, the hydrogen sulfide detector is a YT-95H-H2S-A fixed hydrogen sulfide alarm.

[0027] The present invention has at least the following beneficial effects:

[0028] 1. The present invention is a safe and environmentally friendly construction method for soil containing hydrogen sulfide, which optimizes equipment and construction technology to ensure safe and efficient construction of soil containing hydrogen sulfide.

[0029] 2. In the safe and environmentally friendly construction method for hydrogen sulfide soil of the present invention, the construction method is reasonably set according to the distribution of hydrogen sulfide soil in the outer channel and the inner channel and the ventilation conditions, which takes into account the construction safety while improving the construction efficiency.

[0030] 3. In the safe and environmentally friendly construction method for hydrogen sulfide soil of the present invention, different alarms are arranged and equipped in different areas and for different construction personnel, and different alarm mechanisms are set to ensure the safety of construction personnel.

[0031] 4. In the safe and environmentally friendly construction method for hydrogen sulfide-containing soil of the present invention, by making full use of the physical property of hydrogen sulfide gas that it diffuses quickly in the wind, the wind direction and wind speed are reasonably utilized, and the appropriate wind direction is selected for construction, which facilitates the reasonable arrangement of construction production on ships and reduces the impact of hydrogen sulfide gas on construction safety.

[0032] 5. In the safe and environmentally friendly construction method for hydrogen sulfide-containing soil of the present invention, the mud concentration in the mud tank is further diluted by loading and ballasting before construction, thereby accelerating the volatilization and dissolution of hydrogen sulfide. By modifying the plow teeth into double-sided ones, the crushing effect of the rake head on the soil in the construction area is increased during construction, and the characteristics of the plow teeth are fully utilized to turn over the seabed soil. The effect of high-pressure water flushing is superimposed to fully disperse the turned soil and release the hydrogen sulfide gas in the soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG1 is a schematic flow diagram of a safe and environmentally friendly construction method for hydrogen sulfide-containing soil according to the present invention;

[0034] FIG2 is a schematic diagram of full-silo replacement construction in the safe and environmentally friendly construction method for hydrogen sulfide-containing soil of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be described in further detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0036] It should be noted that the testing methods in the following embodiments are conventional methods unless otherwise specified, and the materials can be obtained from commercial channels unless otherwise specified.

[0037] <Example 1>

[0038] As shown in Figures 1 and 2, taking the Tanzania Port Basin Channel Dredging Project as an example, a safe and environmentally friendly construction method for soil containing hydrogen sulfide is implemented.

[0039] 1. Situation of soil areas containing hydrogen sulfide:

[0040] 1.1. The dredging project includes the outer channel, channel entrance, turning circle and inner channel area. The dredging volume is about 10 million m 3 Outer Channel 1 is 2,165 meters long, with a base width gradually changing from 240 meters to 190 meters; the curve arc is 1,527 meters long, with a radius of 2,040 meters and a base width gradually changing from 210 meters to 170 meters; Outer Channel 2 is 1,222 meters long, with a base width gradually changing from 210 meters to 170 meters; the channel entrance is 1,309 meters long, with a base width of varying widths; the turning circle radius is 260 meters; the inner channel is 1,778 meters long, with a base width gradually changing from 210 meters to 170 meters.

[0041] Soil containing hydrogen sulfide is mainly distributed in the outer channel and the inner channel, the port channel and the turning circle in the middle area. The construction soil is mainly sand, and there is no soil containing hydrogen sulfide.

[0042] 1.2. Flow velocity in the construction area: The area within the mouth is a semi-enclosed harbor. Except for the influence of rising and falling tides, the flow velocity in the harbor is about 0.2 m / s. The main water flow in the coastal waters outside the port area is the South Equatorial Current, with a velocity ranging from 0.5 to 0.6 m / s and flowing in the northeast direction.

[0043] 1.3. Ocean Waves: From January 2001 to December 2020, the general direction of ocean waves was found to be: offshore, the dominant direction was east-southeast, with the highest waves originating from the south-southeast direction; the minimum recorded significant wave height was 0.8 m, and the annual average wave height was 1.6 m; the maximum wave height was 4.6 m on August 12, 2010, at 174°N (southeast); 70% of waves oriented east to south, and 30% from north to east; from April to November, the dominant wave direction was southeast, with the highest waves occurring from June to August. In coastal areas, the highest waves emanated from the northeast, with maximum heights ranging from 2.4 to 3.4 m.

[0044] 1.4. Tide: The local tide is regular semi-diurnal, with high tide of 3.2m and low tide of 1.2m.

[0045] 1.5. The project site enjoys a tropical savanna climate, characterized by mild and dry weather and minimal fog year-round. Even occasional, brief periods of fog only minimally impact construction. The area is subject to the monsoon, with the construction period from December to March primarily influenced by northerly and northeasterly winds; the construction period from April to September primarily influenced by southeasterly and southwesterly winds. Based on statistical analysis of the two time periods and the wind and wave resistance capabilities of our vessels, the wind conditions in this area have minimal impact on our construction vessels.

[0046] 1.6. Hydrogen sulfide soil conditions: Hydrogen sulfide-containing soil is mainly silt, containing shell fragments and organic matter, and is very soft to soft. The moisture content of the mud surface is 100%, the moisture content 10m below the mud surface is 50%, the organic matter content is 8% to 16%, the undrained shear strength 2m below the mud surface is 2kPa, and the undrained shear strength 10m below the mud surface is 15kPa.

[0047] 2. Hazards of hydrogen sulfide:

[0048] Hydrogen sulfide is an inorganic compound with the chemical formula H2S. It is a flammable, explosive, highly toxic and corrosive gas. Under normal circumstances, it is a colorless gas with a typical rotten egg smell. Its relative molecular mass is 34.08 and its density is 1.539 kg / m 3 The relative density to air is 1.19, the melting point is -82.9℃, the boiling point is -60.3℃, and it is soluble in water. At 0℃, 1 mol of water can dissolve about 2.6 mol of H2S. Its solubility decreases with the increase of water temperature.

[0049] 2.1 Flammability

[0050] It forms a flammable mixture with air, with the lowest autoignition temperature (260°C) occurring at a concentration of approximately 15%. At higher concentrations or when oxygen is insufficient, combustion forms water and sulfur: 2H2S + O2 = 2H2O + 2S↓. At lower concentrations or when oxygen is sufficient, combustion products form water and sulfur dioxide: 2H2S + 3O2 = 2H2O + 2SO2. Combustion produces a pale blue flame and SO2 gas, which is harmful to the eyes and lungs. Inhaling small amounts of high concentrations of H2S can be fatal in a short period of time, even when oxygen is insufficient. Low concentrations of H2S can affect the eyes and central nervous system.

[0051] 2.2 Explosiveness

[0052] When the H2S concentration is between 4.3% and 46%, the mixed gas formed in the air will produce a violent explosion when it encounters fire.

[0053] 2.3 Toxicity

[0054] H2S gas is highly toxic and can easily cause death. It is 5 to 6 times more toxic than carbon monoxide. A person's sensitivity to H2S decreases with repeated exposure, with the second exposure being more dangerous than the first, and so on. When inhaled, H2S is transported through the respiratory tract, lungs, and bloodstream to various organs. It first irritates the respiratory tract, dulling the sense of smell and causing coughing, and in severe cases, burns; it stings the eyes and can lead to blindness; it stimulates the nervous system, causing dizziness, loss of balance, and difficulty breathing; and it accelerates the heartbeat, leading to cardiac hypoxia and death in severe cases. Alcohol in the bloodstream increases the risk of H2S poisoning.

[0055] The effects of H2S depend on the duration of exposure and the concentration at which it occurs. Individual health conditions vary, making it difficult to provide a set of fixed rules. H2S concentrations are usually expressed in ppm (parts per million), but the general pattern of how different concentrations affect people is as follows: Under normal circumstances, repeated exposure to 10 ppm is the average concentration that the body can tolerate. This concentration is known as the threshold limit value (THL). For short exposures throughout the day, concentrations can be raised to 15 ppm for a maximum of 15 minutes. This concentration can be increased up to four times a day, separated by at least 60 minutes, to achieve the short-term exposure limit (SEL).

[0056] 3. Construction technology

[0057] 3.1 Equipment:

[0058] Vessels: Trailing Suction Barge (Tongxu, used for dredging), grab vessel group (obstacle salvage and dredging): Tianjin Hangjun 407 (grab), Tianjin Hangbae 48 (mud barge), Tianjin Hangbae 49 (mud barge) and Tianjin Hangbae 51 (mud barge), boat (Darun 66, emergency rescue).

[0059] Other equipment: 40 gas masks (EHFR-5000, gas protection), 13 cabinet fans (KS-04X60Dg, ventilation), 10 four-in-one gas detectors (detection), 20 portable hydrogen sulfide gas detectors (CLIP-H2S, detection), 6 explosion-proof axial flow fans (1000w, 3000w, ventilation), 5 oxygen cylinders and breathing masks (gas protection), 57 emergency respirators (THB / 15-I, gas protection), 30 fixed hydrogen sulfide monitoring probes (YT-95H-H2S-A, detection), 30 sound and light alarms (detection), 1 monitoring host (32 channels, integrated monitoring) and 1 monitoring host (16 channels, integrated monitoring).

[0060] 3.2. Investigation of construction area conditions:

[0061] Currently, the soils containing H2S are known to be located in the outer and inner channels. Contact with the contractor who previously worked on the site revealed similar conditions during their work. However, the contractor used a grab vessel, resulting in minimal disturbance and no widespread eruption. Soil samples were sent to the laboratory, but no H2S levels were found to exceed the standard, so no treatment was performed. A preliminary on-site investigation indicates that the H2S in this area is caused by the decomposition of animal remains, which form H2S gas and is dispersed throughout the construction soil.

[0062] The mud layer in the outer channel is thin, open and unobstructed, with good ventilation conditions. Although there were H2S alarm values ​​during construction, the monitored H2S gas concentration values ​​were all within the safe range.

[0063] A large amount of H2S-containing soil is distributed in the inner channel. This area is located in a semi-enclosed area within the port and is surrounded by urban buildings. The wind force is small and the gas diffusion conditions are poor. In addition, the soil layer is about 2m thick and has a high H2S content. This is the difficulty and focus of the H2S soil construction in this project.

[0064] 3.3, Construction process:

[0065] Step 1: Arrange hydrogen sulfide detectors: According to the ship type and layout of the "Tongxu", the monitoring range of the H2S detector is 20-50m 2 30 fixed H2S detectors and two monitoring hosts were installed on the Tongxu. Each H2S detector was 30-60cm above the ground and secured with a steel frame. The specific layout was as follows: 21 in the engine room and 9 in the cabin and bridge. The 21 H2S detectors in the engine room were connected in parallel to a 32-channel monitoring host, which was placed in the engine room monitoring room. Nine H2S detectors were installed in the cabin and bridge, connected in parallel to a 16-channel monitoring host, which was placed on the bridge. The specific installation distribution is shown in Table 1 below.

[0066] Each construction worker is equipped with a portable hydrogen sulfide gas detector. When the concentration of hydrogen sulfide in the air is greater than 10ppm, the detector will emit a buzzer alarm. When the concentration of hydrogen sulfide in the air is greater than 15ppm, the detector will emit a buzzer alarm and the red alarm light will flash;

[0067] Each vessel at the construction site is equipped with two four-in-one gas detectors to monitor hydrogen sulfide and other toxic gases in the air;

[0068] Among them, the hydrogen sulfide detector is the YT-95H-H2S-A fixed hydrogen sulfide alarm, and the detection alarm is a two-level alarm mechanism, specifically including:

[0069] When the hydrogen sulfide detector detects a concentration greater than 10ppm and less than 20ppm, the detector will sound a buzzer and a yellow alarm light will be displayed. Construction personnel will wear hydrogen sulfide respirators and continue construction. The ship's position will be adjusted according to the wind direction so that the bridge, respirators, and engine room monitoring room are all upwind. When the hydrogen sulfide detector detects a concentration greater than 20ppm, the detector will sound a buzzer and a red alarm light will be displayed. Construction personnel will urgently wear respirators, immediately stop construction and move away from the construction area, and conduct high-pressure water flushing and ventilation in the construction area.

[0070] Step 2: Optimization of construction equipment:

[0071] Keels are welded around and above the ship's mud tank, and the tank is sealed with a sealing membrane. The sealed area is 15-20 meters from the side of the bridge and 10 meters aft of the tank. A high-power axial flow fan is installed in the middle area. The mud door holes on the mud tank deck are filled with expanding foam and blocked with a cover plate on the outside. To maximize the release of H2S gas in the soil, double-sided plow teeth are installed on the wear-resistant blocks of the rake head. This increases the crushing effect of the rake head on the soil in the construction area during construction. The plow teeth are fully utilized to turn the seabed soil. The high-pressure water flushing effect is superimposed to fully disperse the turned soil and release the H2S gas in the soil. The sealing membrane is a special fabric membrane, and its specific use is not limited, as long as it can achieve the purpose of sealing the mud tank.

[0072] Each cabin is equipped with a high-power cabinet fan; 3000W high-power explosion-proof axial flow fans are placed near the main deck mud tank, the main engine room, the pump room, the hydraulic room, and the engine room repair room. Hydrogen sulfide respirators and emergency breathing apparatus (as needed) are provided in the cabins, pump room, engine room monitoring room, and bridge. The emergency breathing apparatus has a 10-15 minute lifespan and should be worn when the general sound alarm system sounds or the H2S gas detector detects excessive H2S concentration. Personnel wearing this equipment are only required for "escape," not for "work" or rescue. See Table 2 for its distribution.

[0073] Step 3: Construction:

[0074] Before construction, inject mud into the cabin, adopt the highest overflow, close the front loading cabin, open the high-pressure water flushing of the drag head at the wear-resistant block and the inside of the drag chamber, adjust the angle of the drag lip upward to separate the drag lip from the mud surface, and use high-pressure water flushing to break up the mud on the seabed first, so that the H2S will evaporate or dissolve into the water first. If the high-pressure water flushing pressure is low, two high-pressure water flushing pumps can be connected in series to one drag head for use, and single-drag construction can be adopted (one drag head on the side with high-pressure water flushing is used for dredging, and the other drag head uses a combined pump to pump clean water into the cabin, so that the mud concentration in the mud cabin will be further diluted, accelerating the volatilization and dissolution of H2S.

[0075] Before construction, disperse the hydrogen sulfide gas in the cabin to ensure that the concentration of hydrogen sulfide in the cabin is within the normal range.

[0076] During the construction process, the fans in the ship's cabins are turned off for external circulation and turned on for internal circulation, and explosion-proof axial flow fans are used for ventilation to speed up air flow. During the construction process, it is necessary to select the appropriate wind direction for construction, analyze the main wind direction, secondary dominant wind direction and wind speed, and at the same time check the direction of the ship's construction channel, make full use of the physical property of H2S gas that diffuses quickly in the wind, and reasonably use the wind direction and wind speed to reduce the impact of H2S gas on construction safety. The ship needs to observe the relative wind direction of the ship at any time based on the wind direction and speed meter, so as to facilitate the ship to reasonably arrange construction production and try to work against the wind and crosswind. Specifically including:

[0077] When there is no wind, increase the speed by 2.5-3 knots to reduce the time hydrogen sulfide gas accumulates on the ship;

[0078] When the wind is blowing against you, continue construction as normal and pay close attention to the alarms of the multiple hydrogen sulfide detectors installed on the ship. Fans in the cabins of the ship should switch off external circulation and on to internal circulation mode, and explosion-proof axial flow fans should be kept running.

[0079] When the wind is crosswind, construction should be carried out in the inner channel area where the hydrogen sulfide gas is high; the explosion-proof axial flow fan should be kept on;

[0080] When the wind is favorable, the ship stops working;

[0081] After construction is completed and en route to the mud dumping area, the vessel utilizes mechanical and natural ventilation to promptly complete internal cabin ventilation. After ventilation, the vessel's dedicated detection personnel use detection equipment to conduct detection in each cabin. Once there is no H2S risk, normal operations begin. During mud dumping, the vessel maintains mud dumping against or across the wind to reduce the potential release of H2S. Thirty minutes before mud dumping is complete and before arriving at the construction area, the ship's bridge notifies the engine room of the start time of construction. Non-operating personnel remain on standby in the cabin, while operating personnel prepare protective gear for operation. Bridge operators prepare for construction, and upon arrival at the construction area, construction continues according to the aforementioned construction process.

[0082] During ship construction, attention was paid to the crew's personal protection while the ship was being modified. During loading, H2S-containing mud crashed from the hatchway onto the tank bottom, converting potential energy into kinetic energy, releasing a large amount of H2S gas. The H2S gas then recoiled along the mud bulkhead to the upper part of the tank, where it then diffused, resulting in a higher density at higher points than at lower points.

[0083] Keels are welded around and above the mud tank, and a special cloth film is used to seal the mud tank. The sealed area is about 15-20 meters from the bridge side and 10 meters behind the mud tank. A high-power axial flow fan is installed in the middle area to disperse H2S and prevent H2S gas from entering the cabin from the front and rear air inlets, ensuring that the H2S concentration values ​​inside the bridge, living cabin and engine room are within the normal range.

[0084] The inside of the 24 small mud door holes on the mud tank deck are filled with expanding foam and sealed with special cover plates on the outside to prevent H2S from being released outwards through these holes during construction (no small mud door operation is required for digging and throwing operations).

[0085] If H2S gas is detected in the dredged material during construction, deck operations are strictly prohibited. The Chief Officer and Second Engineer are responsible for the opening and closing of the deck and engine room compartments, respectively. Hatch doors must not be opened during construction. When leaving the H2S area during raking and dumping, ventilate the area promptly and abundantly. Dump mud into or across the wind.

[0086] Ship drivers should promptly observe changes in wind direction and speed, maintain navigational observations and lookouts, pay close attention to H2S concentration monitoring at all times, and make preparations for H2S protection.

[0087] Table 1. Distribution of fixed H2S detectors on ships

[0088] Table 2. Distribution of emergency respirators

[0089] The construction speed calculation is achieved as follows:

[0090] The H2S concentration area is 2000m long. To prevent H2S accumulation during construction in this area, a method is implemented to leave the H2S concentration area after one hour of construction and proceed to other construction areas. The turning time during construction is 8 minutes, excluding the ballasting time before construction. Therefore, the construction speed in this area is calculated as:

[0091] Length of construction area ÷ 1852 × one round trip ÷ (1 hour - 8 minutes / 60)

[0092] 2000÷1852×2÷(1-8 / 60)=2.5kn

[0093] Therefore, in order to reduce the time that the "Tongxu" spends constructing in the H2S concentration area, the construction speed in this area is controlled at 2.5kn.

[0094] Calculation of hydrogen sulfide retention time on the hull:

[0095] The Tongxu is a forecastle-type vessel with a rake at the stern. Dual rakes rake the seabed, disturbing the soil and causing H2S gas to escape. The vessel has already left the area before the H2S rises to the surface, posing little threat to the vessel. However, the H2S gas, once released from the soil in the mud tanks by the dredge pumps, remains on the vessel.

[0096] An analysis of the turbulent flow field characteristics surrounding a square bluff body reveals that when the incoming flow impacts the cube, the bluff body blocks the flow, causing the velocity of the fluid in the direction of motion to stagnate to zero on the front surface. The fluid then turns 90° and accelerates perpendicularly, causing complex changes in the boundary layer around the bluff body. Because the velocity at the bluff body wall is zero, the fluid flowing through the 90° corner experiences changes in viscous forces and the formation of vortices. This separation occurs at the top front corner of the cube, and after bypassing the bluff body, a periodic shedding Karman vortex street forms at the rear.

[0097] The distance between the front end of the Tongxu mud tank and the stern is 105m. The position of the ship is the engine room. After the H2S is released, the ship continues to move forward. The H2S above the mud tank will gradually leave the ship. The time from stopping the pump to the dissipation of H2S on the ship is calculated as:

[0098] Length of the inlet pipe system ÷ flow rate + diffusion time of H2S-containing mud + retention time of H2S in the hull:

[0099] 60÷6÷60+1+105÷(2.5÷1.852)÷60=2.5min

[0100] That is, after the ship stops pumping, 2.5 minutes later, the H2S diffused above the ship will basically leave the hull.

[0101] Time for hull replacement with fresh air:

[0102] Tongxu's total cabin volume is 30,300m 3

[0103] The fan flow rate is 48000m 3 / h

[0104] Time required to replace the hull with fresh air = 30300÷48000×60=38min

[0105] That is, after the ship stops working, the whole ship will replace the fresh air once after 38 minutes. If it is confirmed that there is no risk, the hatch will be opened to speed up the air change.

[0106] In summary, the safe and environmentally friendly construction method for hydrogen sulfide-containing soil of the present invention ensures safe and efficient construction of hydrogen sulfide-containing soil by rationally optimizing equipment and construction technology.

[0107] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and exemplary embodiments. They can be applied to a variety of fields suitable for the present invention. Further modifications will be readily apparent to those skilled in the art. Therefore, the present invention is not limited to the specific details and illustrations shown and described herein without departing from the general concept defined by the claims and their equivalents.

Claims

1. A safe and environmentally friendly construction method for soil containing hydrogen sulfide, characterized in that: The following steps are involved: Step 1: Arrange hydrogen sulfide detectors: Arrange multiple hydrogen sulfide detectors and two monitoring hosts on the construction ship, with each hydrogen sulfide detector 30 to 60 cm above the ground; Step 2: Optimization of construction equipment: Weld keels around and above the ship's mud tank, and use closed membrane to seal the mud tank. The closed area is 15-20 meters near the side of the driving platform and 10 meters behind the mud tank. A high-power axial flow fan is arranged in the middle area. The mud door hole on the mud tank deck is filled with expanding foam inside and blocked with a cover plate outside. Double-sided plow teeth are installed on the wear-resistant block of the ship's rake head. Step 3. Construction: Before construction, disperse the hydrogen sulfide gas in the cabin to ensure that the hydrogen sulfide concentration in the cabin is within the normal range. During the construction process, the fan in the cabin of the ship turns off the external circulation, turns on the internal circulation mode, and uses explosion-proof axial flow fans to accelerate air flow.

2. The safe and environmentally friendly construction method for soil containing hydrogen sulfide as claimed in claim 1, characterized in that: In step 1, the detection alarm of the hydrogen sulfide detector is a secondary alarm mechanism, which specifically includes: When the hydrogen sulfide detector detects that the concentration of hydrogen sulfide is greater than 10ppm and less than 20ppm, the detector will emit a buzzer and a yellow alarm light will sound. The construction personnel will wear hydrogen sulfide breathing protection and continue construction. The position of the ship will be adjusted according to the wind direction so that the bridge, breathing apparatus, and engine room monitoring room are all in the upwind position; When the hydrogen sulfide detector detects that the hydrogen sulfide concentration is greater than 20ppm, the detector will emit a buzzer and a red alarm light will sound. The construction workers will immediately wear respirators, stop construction immediately and move away from the construction area, and perform high-pressure flushing and ventilation on the construction area.

3. The safe and environmentally friendly construction method for soil containing hydrogen sulfide as claimed in claim 1, characterized in that: Step three specifically includes: When there is no wind, increase the speed by 2.5-3 knots to reduce the time hydrogen sulfide gas accumulates on the ship; When the wind is blowing against you, work should be carried out normally, and the alarm of multiple hydrogen sulfide detectors arranged on the ship should be paid attention to in real time. The fans in the cabins of the ship should be turned off for external circulation, turned on for internal circulation, and explosion-proof axial flow fans should be kept on normally. When the wind is crosswind, construction should be carried out in the inner channel area where the hydrogen sulfide gas is high; the explosion-proof axial flow fan should be kept on; When the wind is favorable, the ship stops construction.

4. The safe and environmentally friendly construction method for soil containing hydrogen sulfide as claimed in claim 1, characterized in that: The quality inspection of step three and step two also includes: loading and ballast before construction: before construction, fill the ship's cabin with mud, use the highest overflow, close the front loading cabin, open the rake head to high-pressure flush the wear-resistant block and one place inside the rake cavity, and adjust the angle of the rake lip upward to separate the rake lip from the mud surface.

5. The safe and environmentally friendly construction method for soil containing hydrogen sulfide as claimed in claim 1, characterized in that: Step one also includes: equipping each construction worker with a portable hydrogen sulfide gas detector. When the concentration of hydrogen sulfide in the air is greater than 10ppm, the detector will emit a buzzer alarm. When the concentration of hydrogen sulfide in the air is greater than 15ppm, the detector will emit a buzzer alarm and the red alarm light will flash.

6. The safe and environmentally friendly construction method for soil containing hydrogen sulfide as claimed in claim 1, characterized in that: Step one also includes: Each ship at the construction site is equipped with two four-in-one gas detectors to monitor the presence of hydrogen sulfide and other toxic gases in the air.

7. The safe and environmentally friendly construction method for soil containing hydrogen sulfide as claimed in claim 1, characterized in that: Step two also includes: equipping each room in the ship's living quarters with a high-power cabinet fan; placing 3000w high-power explosion-proof axial fans in the main engine room, pump room and repair room; equipping the living quarters, pump room, engine room monitoring room and navigation station with hydrogen sulfide breathing protective devices and emergency respirators that meet the needs.

8. The safe and environmentally friendly construction method for soil containing hydrogen sulfide as claimed in claim 1, characterized in that: Step three also includes: during the mud throwing process, the vessel keeps throwing mud against the wind or across the wind.

9. The safe and environmentally friendly construction method for soil containing hydrogen sulfide as claimed in claim 1, characterized in that: In step one, 30 hydrogen sulfide detectors are installed, all of which are fixed with steel frames. There are two monitoring hosts with specific installation locations: 21 in the engine room, and 9 in the cabin and the bridge. The 21 hydrogen sulfide detectors in the engine room are connected in parallel with a 32-channel monitoring host, and the 32-channel monitoring host is placed in the engine room monitoring room. The 9 hydrogen sulfide detectors installed in the cabin and the bridge are connected in parallel with a 16-channel monitoring host, and the 16-channel monitoring host is placed on the bridge.

10. The safe and environmentally friendly construction method for soil containing hydrogen sulfide as claimed in claim 9, characterized in that: The hydrogen sulfide detector is a YT-95H-H2S-A fixed hydrogen sulfide alarm.

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