Ammonia fuel ship tail gas denitration system and method

Abstract

The invention relates to a tail gas denitration system and method for an ammonia fuel ship, an ammonia supply pipeline of an ammonia fuel engine in the system adopts a double-wall pipe, the inner pipe of the double-wall pipe is used for conveying liquid ammonia, and the outer pipe of the double-wall pipe is connected with an ammonia treatment system through a fan so as to suck leaked ammonia gas to the ammonia treatment system; the ammonia treatment system is connected with the buffer tank through a fan and is used for conveying the discharged gas to the buffer tank after pressurizing the discharged gas through the fan; the ammonia treatment system is connected with a reducing agent tank through a pump; the reducing agent tank receives ammonia water of the ammonia treatment system through the pump; the SCR reducing agent supply system is connected with the reducing agent spray gun through the reducing agent tank and the buffer tank and used for conveying the discharged gas to the reducing agent spray gun through the SCR reducing agent supply system to assist in atomizing ammonia water. According to the ammonia fuel ship tail gas denitration system and method, ammonia water generated in the ammonia treatment system is used as a reducing agent of the SCR system, and discharged gas of the ammonia treatment system is used as auxiliary atomization gas of the reducing agent, so that waste is recycled, and the denitration efficiency is improved.

Description

Technical Field

[0001] The present invention relates to ship exhaust gas treatment technology, specifically a denitration system and method for the exhaust gas of ammonia-fueled ships. It uses waste ammonia gas to generate high-concentration ammonia water as a reducing agent for the SCR system, and at the same time uses the bleed gas for auxiliary atomization to achieve energy-saving and efficient denitration. Background Art

[0002] The selective catalytic reduction (SCR) system is a post-treatment technology used to solve the nitrogen oxide (NOx) emissions of engines. It needs to use urea solution or ammonia as a reducing agent to react with NOx to reduce the NOx emissions of the engine. Diesel SCR systems generally use urea solution as a reducing agent. Since ammonia-fueled ships use liquid ammonia as fuel, they need to be equipped with a liquid ammonia storage tank. The liquid ammonia storage tank will generate ammonia evaporation gas (BOG). The ammonia concentration and purity of this part of the ammonia evaporation gas are high. It is processed through the BOG recovery and reuse system. After the BOG is compressed, condensed, liquefied, and separated, it is reused. The ammonia fuel supply pipeline of the engine uses a double-wall pipe. The inner pipe is used to transport liquid ammonia, and the outer pipe is ventilated by a fan. Once a leak occurs, the ammonia gas is extracted by the fan and collected through the ammonia treatment system. When the engine switches between ammonia / diesel operation modes, nitrogen is used to purge the ammonia fuel supply system to remove the residual ammonia in the supply system. The purge gas is introduced into the ammonia treatment system. The ammonia treatment system uses water as a medium to absorb ammonia. When the ammonia concentration in the water gradually increases and the ammonia water reaches saturation at the working temperature and pressure and cannot absorb more ammonia, the ammonia water in the ammonia treatment system needs to be drained and stored, and this part of the ammonia water is processed when the ship is docked. Therefore, the stored ammonia water occupies the cabin space and increases the management cost.

[0003] Traditional SCR systems rely on urea solution or liquid ammonia, and have problems such as high storage costs and high energy consumption. Ammonia-fueled ships need to handle liquid ammonia evaporation gas (BOG) and leaked ammonia gas. Existing technologies need to additionally drain ammonia-containing wastewater, occupying the cabin space. Patent CN118526944A mentions using low-concentration ammonia water for denitration, but does not solve the problems of ammonia water generation and atomization optimization. The present invention integrates the ammonia treatment system and the SCR system to achieve waste reuse and improve the denitration efficiency. Summary of the Invention

[0004] The present invention aims to propose a denitration system and method for the exhaust gas of ammonia-fueled ships, which uses the waste (bleed gas from the ammonia treatment system, mainly composed of air and nitrogen) during the operation of the ammonia-fueled engine as the auxiliary atomization gas for ammonia water, realizes waste reuse, and improves the denitration efficiency.

[0005] To achieve the above object, the technical solution of the present invention is: an ammonia fuel ship tail gas denitration system, including: an ammonia fuel engine, a liquid ammonia storage tank, an ammonia fuel supply system, an ammonia fuel valve group unit, an ammonia treatment system, and an SCR reductant supply system. The ammonia supply pipeline of the ammonia fuel engine uses a double-walled pipe. The inner pipe of the double-walled pipe is used to transport liquid ammonia, and the outer pipe is connected to the ammonia treatment system through a fan to suck the leaked ammonia gas to the ammonia treatment system; the ammonia treatment system is connected to a buffer tank through a fan to pressurize and transport the vent gas to the buffer tank through the fan; the ammonia treatment system is connected to a reductant tank through a pump, and the reductant tank receives the ammonia water from the ammonia treatment system through a pump; the SCR reductant supply system is connected to a reductant spray gun through the reductant tank and the buffer tank to transport the vent gas to the reductant spray gun through the SCR reductant supply system to assist in atomizing the ammonia water.

[0006] Furthermore, the ammonia treatment system is also connected to the ammonia fuel storage tank through a valve. When the engine operates in diesel mode, after the valve is opened, a part of the ammonia BOG can be introduced into the ammonia treatment system to generate sufficient ammonia water.

[0007] Furthermore, the ammonia treatment system is also provided with a regulating valve to control the working pressure of the ammonia treatment system by adjusting the opening of the regulating valve to ensure that the mass fraction of ammonia water in the ammonia treatment system 7 is ≥20% under the working temperature and working pressure.

[0008] Furthermore, the ammonia fuel engine is connected to the ammonia fuel valve group unit through a double-walled pipe, and the ammonia fuel valve group unit is connected to the ammonia treatment system and the ammonia fuel supply system.

[0009] Furthermore, the ammonia treatment system adopts a scrubber or a dispersion tank structure form.

[0010] Furthermore, multiple reductant tanks and buffer tanks are provided to support redundant backup.

[0011] Furthermore, the SCR reductant supply system calculates the ammonia water dosage according to the exhaust NOx concentration, flow rate, and ammonia water mass fraction through the formula

[0012]

[0013] where M is the ammonia water dosage, V is the volume flow rate of the exhaust gas under standard conditions, α is the ammonia-nitrogen ratio, ρ is the density of ammonia water, and w is the mass fraction of ammonia water.

[0014] An ammonia fuel ship tail gas denitration method, based on the ammonia fuel ship tail gas denitration system, the steps are as follows:

[0015] a. Collect the leaked ammonia gas from the double-walled pipe and the residual ammonia gas from nitrogen purging to the ammonia treatment system;

[0016] b. Generate ammonia water with a mass fraction ≥20% in the ammonia treatment system and store it in the reductant tank;

[0017] c. Pressurize the vent gas from the ammonia treatment system to assist in atomizing ammonia water;

[0018] d. Dynamically adjust the ammonia injection amount according to the exhaust parameters.

[0019] Furthermore, in diesel mode, the BOG portion of the liquid ammonia storage tank is introduced into the ammonia treatment system until the mass fraction of ammonia water reaches 20% and then the valve is closed, and air is used as a reducing agent to assist in the supplement of atomizing gas.

[0020] Furthermore, when the ammonia fuel engine switches between ammonia / diesel operating modes, nitrogen is used to purge the ammonia fuel valve assembly unit and the ammonia fuel engine to remove residual ammonia in the ammonia fuel valve assembly unit and the ammonia fuel engine, and the ammonia contained in the purge nitrogen is collected by the ammonia treatment system.

[0021] The beneficial effects of the present invention are:

[0022] The present invention provides an ammonia fuel ship exhaust denitrification system and method, which uses ammonia water generated in an ammonia treatment system as a reductant for an SCR system, and uses the vented gas of the ammonia treatment system as an auxiliary atomizing gas for the reductant. The decomposition of ammonia water to generate ammonia gas only requires a physical evaporation process, and does not require a chemical decomposition process. Therefore, compared with urea solution, the use of ammonia water as a reductant is more conducive to fully generating ammonia gas before the SCR catalyst and improving the SCR denitrification efficiency. When the engine is running in diesel mode, the ammonia supply system stops working, and air is used as a reductant to supplement the auxiliary atomizing gas. In order to obtain enough ammonia water for the SCR system, a part of the ammonia BOG in the liquid ammonia storage tank is passed into the ammonia treatment system to generate ammonia water with a mass fraction of 20% or more. The present invention reuses the waste generated during the operation of the ammonia fuel engine, which can save the energy consumption of the SCR system auxiliary atomization compressed air; save urea reductant, improve the denitrification efficiency of the SCR system; and save cabin space without setting up a urea storage tank.

[0023] The core innovations of the present invention are:

[0024] 1. System composition:

[0025] (1) The ammonia treatment system 7 absorbs leaked and purged ammonia gas to generate high-concentration ammonia water;

[0026] (2) The SCR system uses ammonia water instead of urea, and blowdown gas instead of compressed air atomization;

[0027] (3) Dynamically adjust the ammonia treatment system pressure to maintain ammonia saturation.

[0028] 2. Method flow:

[0029] (1) Leaked ammonia gas and purge nitrogen gas are introduced into the ammonia treatment system to generate ammonia water;

[0030] (2) The vent gas is used for ammonia atomization after being pressurized;

[0031] (3) Dynamically calculate the ammonia injection amount according to the exhaust parameters.

[0032] III. Technical effects:

[0033] (1) Save urea and compressed air, and reduce energy consumption;

[0034] (2) Eliminate the need for ammonia wastewater storage and optimize the cabin space;

[0035] (3) Improve the ammonia generation efficiency and the SCR denitration performance. Description of the drawings

[0036] Figure 1 is the schematic diagram of the ammonia fuel ship exhaust gas denitration system of the present invention;

[0037] In the figure: 1. Ammonia fuel engine; 2. Liquid ammonia storage tank; 3. Ammonia fuel supply system; 4. Ammonia fuel valve group unit; 5. Double-walled pipe; 6. Fan; 7. Ammonia treatment system (scrubber / dispersion tank); 8. Pump; 9. Reducing agent tank; 10. Fan; 11. Buffer tank; 12. SCR reducing agent supply system; 13. Reducing agent spray gun; 14. Valve; 15. Regulating valve; 16. Regulating valve.

[0038] The arrows indicate the connection relationships of each pipeline. Among them, line A - ammonia water pipeline, line B - liquid ammonia pipeline, line C - ventilation air pipeline, line D - ammonia evaporation gas pipeline, line E - ammonia relief and nitrogen purging pipeline, line F - nitrogen purging pipeline, line G - air pipeline. Detailed implementation manners

[0039] The present invention will be further described below in conjunction with the drawings and embodiments.

[0040] As Figure 1 shown, an ammonia fuel ship exhaust gas denitration system provided by an embodiment of the present invention includes an ammonia fuel engine 1, a liquid ammonia storage tank 2, an ammonia fuel supply system 3, an ammonia fuel valve group unit 4, a double-walled pipe 5, a fan 6, an ammonia treatment system 7, a pump 8, a reducing agent tank 9, a fan 10, a buffer tank 11, an SCR reducing agent supply system 12, a reducing agent spray gun 13, a valve 14, a regulating valve 15, and a regulating valve 16. The ammonia fuel ship is provided with an ammonia fuel engine 1, an ammonia fuel storage tank 2, an ammonia fuel supply system 3, and an ammonia fuel valve group unit 4.

[0041] For the ammonia supply pipeline of the ammonia fuel engine 1, a double-wall pipe 5 is adopted. The inner pipe is used to transport liquid ammonia, and the outer pipe is connected to the ammonia treatment system 7 through a fan 6 to suck the leaked ammonia gas into the ammonia treatment system 7; the ammonia treatment system 7 is connected to a buffer tank 11 through a fan 10 to transport the relief gas to the buffer tank 11 after pressurization by the fan 10; the buffer tank 11 is used to store the relief gas of the ammonia treatment system 7 and assist in atomizing ammonia water after pressurization by the fan 10; the reductant tank 9 is connected to the ammonia treatment system 7 through a pump 8, and the reductant tank 9 receives the ammonia water of the ammonia treatment system 7 through the pump 8; an SCR reductant supply system 12 is connected between the reductant tank 9 and the buffer tank 11 and the reductant spray gun 13. When the SCR system works, the relief gas is transported to the reductant spray gun 13 through the reductant supply system 12 to assist in atomizing ammonia water. This system uses the waste ammonia gas of the ship to generate high-concentration ammonia water as the SCR reductant, saving urea and compressed air and improving the denitrification efficiency.

[0042] In addition, the ammonia treatment system 7 is also connected to the ammonia fuel storage bin 2 through a valve 14. After the valve 14 is opened, a part of the ammonia BOG can be introduced into the ammonia treatment system 7. The ammonia treatment system 7 is also provided with a regulating valve 15 to determine the required working pressure according to the ammonia water temperature detected online inside it, and control the working pressure of the ammonia treatment system 7 through the opening degree of the regulating valve 15 to ensure that the mass fraction of the ammonia water inside the ammonia treatment system 7 can reach 20% or more at the working temperature and working pressure.

[0043] The ammonia fuel engine 1 is connected to the ammonia fuel valve group unit 4 through the double-wall pipe 5, and the ammonia fuel valve group unit 4 is connected to the ammonia treatment system 7 and the ammonia fuel supply system 3. When the ammonia / diesel operation mode of the ammonia fuel engine 1 is switched, nitrogen is used to purge the ammonia fuel valve group unit 4 and the ammonia fuel engine 1 to remove the residual ammonia inside the ammonia fuel valve group unit 4 and the ammonia fuel engine 1, and the ammonia contained in the purged nitrogen is collected through the ammonia treatment system 7.

[0044] Preferably, the ammonia treatment system 7 adopts the structural form of a scrubbing tower or a dispersion tank.

[0045] Preferably, one or more pumps 8 and reductant tanks 9 are provided to store the ammonia water with qualified concentration.

[0046] Preferably, one or more fans 10 and buffer tanks 11 are provided to store the relief gas of the ammonia treatment system 7.

[0047] Preferably, the ammonia treatment system 7 is used to absorb the leaked ammonia gas from the double-wall pipe 5 and the residual ammonia gas after nitrogen purging, and generate ammonia water with a mass fraction ≥20%.

[0048] An ammonia fuel ship exhaust gas denitrification method provided by an embodiment of the present invention, based on the above ammonia fuel ship exhaust gas denitrification system, uses the ammonia water generated in the ammonia treatment system 8 as the reducing agent for the SCR system, and uses the vent gas of the ammonia treatment system 8 as the auxiliary atomizing gas for the reducing agent. The decomposition of ammonia water into ammonia only requires a physical evaporation process and does not require a chemical decomposition process. Therefore, compared with urea solution, using ammonia water as the reducing agent is more conducive to fully generating ammonia in front of the SCR catalyst and improving the SCR denitrification efficiency.

[0049] Diesel SCR systems generally use urea solution as the reducing agent. Since ammonia fuel ships use liquid ammonia as fuel, they are equipped with liquid ammonia storage tanks. The liquid ammonia storage tank will generate ammonia evaporation gas (BOG). The ammonia concentration and purity of this part of the ammonia evaporation gas are high. It is processed through the BOG recovery and reuse system, and the BOG is compressed, condensed, liquefied, and separated for reuse.

[0050] The ammonia supply pipeline of the ammonia fuel engine 1 adopts a double-wall pipe 5. Its inner pipe is used to transport liquid ammonia, and the outer pipe is connected to the fan 6. Once a leak occurs, the ammonia gas is extracted by the fan 6, and the ammonia contained in the ventilation air is collected through the ammonia treatment system 7.

[0051] The ammonia treatment system 7 uses water as the medium for absorbing ammonia. When the concentration of ammonia in the water gradually increases and the ammonia mass fraction reaches 20% or more, the ammonia water in the ammonia treatment system is transported to the reducing agent tank 9 through the pump 8. When the SCR system operates, the ammonia water in the reducing agent tank 9 is transported to the reducing agent spray gun 13 through the SCR reducing agent supply system 12.

[0052] The vent gas of the ammonia treatment system 7 is pressurized by the fan 10 and then transported to the buffer tank 11. When the SCR system operates, the vent gas is transported to the reducing agent spray gun 13 through the reducing agent supply system 12 to assist in atomizing the ammonia water.

[0053] When the engine operates in diesel mode, the ammonia supply system stops working, the valve 16 opens, and the fan 10 inhales air as a supplement to the auxiliary atomizing gas of the reducing agent. The ammonia treatment system 7 opens the valve 14 connecting the ammonia fuel storage tank 2 to introduce a part of the ammonia BOG into the ammonia treatment system 7 in order to collect ammonia water with a sufficient concentration for the operation of the SCR system. When the ammonia mass fraction in the ammonia treatment system 7 reaches 20% or more, the valve 14 is closed, and at this time, all the BOG is processed by the BOG recovery and reuse system.

[0054] The SCR reducing agent supply system 12 determines the ammonia water dosage required for the SCR system according to the ammonia water mass fraction and density detected online in the reducing agent tank 9. The calculation formula is as follows:

[0055]

[0056] m: ammonia water dosage, l / h

[0057] C: NOx concentration in the exhaust gas, ppm

[0058] V: Volumetric flow rate of the exhaust gas under standard conditions, Nm3 / h

[0059] α: Ammonia-nitrogen ratio, dimensionless

[0060] ρ: Density of aqueous ammonia, g / l

[0061] w: Mass fraction of aqueous ammonia, %

[0062] The ammonia treatment system 7 determines the required working pressure (the gas pressure detected online) according to its internal working temperature (the temperature of the aqueous ammonia detected online). The working pressure of the ammonia treatment system 7 is controlled by adjusting the opening degree of the control valve 15 to ensure that the mass fraction of the aqueous ammonia inside the ammonia treatment system 7 can reach 20% or more under the working temperature and working pressure. The corresponding relationships among the working temperature, working pressure, and mass fraction of the aqueous ammonia of the ammonia treatment system 7 are as follows:

[0063]

[0064] Example: Detect that the temperature of the aqueous ammonia inside the ammonia treatment system 7 is 25°C and the density is 0.91 g / cm 3 . According to the table interpolation, at 25°C and a pressure of 100 kPa, the mass fraction of the aqueous ammonia can reach 31.65%, meeting the requirement of the minimum mass fraction of the aqueous ammonia of 20%. Therefore, the control valve 15 is fully opened, and the ammonia treatment system 7 can work under normal pressure to meet the requirement of the aqueous ammonia concentration of the SCR system. If the actual mass fraction of the aqueous ammonia detected inside the ammonia treatment system 7 is much less than 31.65% at this time, it indicates that the aqueous ammonia inside the ammonia treatment system 7 is not yet saturated and can still continue to absorb ammonia. When the mass fraction of the aqueous ammonia is between 20% and 31.65%, according to the operation of the SCR system, the pump 8 is run in a timely manner to transport the aqueous ammonia to the reductant tank for use by the reductant supply system 12.

[0065] Example 1:

[0066] (1) Generation of aqueous ammonia: The ammonia leaked from the double-wall pipe 5 is drawn into the ammonia treatment system 7 by the fan 6 and mixed with the sprayed water to generate aqueous ammonia. When the mass fraction of the aqueous ammonia reaches 20%, the pump 8 transports it to the reductant tank 9.

[0067] (2) Atomization control: The released gas is pressurized by the fan 10 and temporarily stored in the buffer tank 11, and is mixed with the aqueous ammonia and atomized and sprayed into the tail gas pipe during SCR operation.

[0068] (3) Adaptation to diesel mode: After closing the ammonia fuel supply, the valve 16 is opened, and the fan 10 inhales air as a supplement to the reductant auxiliary atomizing gas. The valve 14 is opened to introduce the BOG into the ammonia treatment system 7 until the aqueous ammonia meets the standard.

[0069] (4) Dynamic adjustment: Through the coordinated adjustment of the temperature sensor and the regulating valve 15, the mass fraction of ammonia water is adjusted to reach 20% or more (for example, at 25°C, 100 kPa corresponds to a mass fraction of 31.65%).

Claims

1. An ammonia fuel ship exhaust denitrification system, characterized in that: include: Ammonia fuel engine, liquid ammonia storage tank, ammonia fuel supply system, ammonia fuel valve unit, ammonia treatment system, SCR reductant supply system. The ammonia supply pipeline of the ammonia fuel engine adopts a double-walled pipe. The inner pipe of the double-walled pipe is used to transport liquid ammonia, and the outer pipe is connected to the ammonia treatment system through a fan to suck the leaked ammonia to the ammonia treatment system; the ammonia treatment system is connected to the buffer tank through a fan, which is used to transport the bleed gas to the buffer tank after being pressurized by the fan; the ammonia treatment system is connected to the reductant tank through a pump, and the reductant tank receives ammonia water from the ammonia treatment system through a pump; the SCR reductant supply system is connected to the reductant spray gun through the reductant tank and the buffer tank, which is used to transport the bleed gas to the reductant spray gun through the SCR reductant supply system to assist in atomizing the ammonia water.

2. The ammonia fuel ship exhaust denitrification system according to claim 1, characterized in that: The ammonia treatment system is also connected to the ammonia fuel storage tank through a valve. When the engine runs in diesel mode, the valve is opened to allow part of the ammonia BOG to pass into the ammonia treatment system to generate sufficient ammonia water.

3. The ammonia fuel ship exhaust denitrification system according to claim 1, characterized in that: The ammonia treatment system is also provided with a regulating valve, and the opening of the regulating valve is used to control the working pressure of the ammonia treatment system to ensure that the mass fraction of ammonia water in the ammonia treatment system 7 is ≥20% at the working temperature and working pressure.

4. The ammonia fuel ship exhaust denitrification system according to claim 1, characterized in that: The ammonia fuel engine is connected to the ammonia fuel valve group unit through a double-walled pipe, and the ammonia fuel valve group unit is connected to the ammonia processing system and the ammonia fuel supply system.

5. The ammonia fuel ship exhaust denitrification system according to claim 1, characterized in that: The ammonia treatment system adopts a scrubbing tower or dispersion tank structure.

6. The ammonia fuel ship exhaust denitrification system according to claim 1, characterized in that: Multiple reducing agent tanks and buffer tanks are provided to support redundant backup.

7. The ammonia fuel ship exhaust denitrification system according to claim 1, characterized in that: The SCR reductant supply system is based on the exhaust NOx concentration, flow rate and ammonia mass fraction through the formula Calculate the amount of ammonia water used, where M is the amount of ammonia water used, V is the volume flow rate under standard exhaust conditions, α is the ammonia nitrogen ratio, ρ is the density of ammonia water, and w is the mass fraction of ammonia water.

8. An ammonia fuel ship exhaust denitrification method, based on the ammonia fuel ship exhaust denitrification system according to any one of claims 1 to 7, characterized in that: The steps are: a. Collect the leaked ammonia from the double-walled pipe and the residual ammonia from nitrogen purge to the ammonia treatment system; b. Generate ammonia water with a mass fraction of ≥20% in the ammonia treatment system and store it in the reducing agent tank; c. Pressurize the vent gas from the ammonia treatment system to assist in atomizing ammonia water; d. Dynamically adjust the ammonia injection amount according to the exhaust parameters.

9. The method for denitrification of exhaust gas from ammonia fuel ships according to claim 8, characterized in that: In diesel mode, the BOG portion of the liquid ammonia storage tank is introduced into the ammonia treatment system until the mass fraction of ammonia water reaches 20% and then the valve is closed, and air is used as a reducing agent to assist in the supplement of atomizing gas.

10. The method for denitrification of exhaust gas from ammonia fuel ships according to claim 8, characterized in that: When the ammonia fuel engine switches between ammonia / diesel operating modes, nitrogen is used to purge the ammonia fuel valve assembly unit and the ammonia fuel engine to remove residual ammonia in the ammonia fuel valve assembly unit and the ammonia fuel engine, and the ammonia contained in the purge nitrogen is collected through the ammonia treatment system.

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