A natural gas supercharger switching pressure stabilizing method without additional energy consumption

Abstract

The present application relates to a kind of natural gas booster switching pressure stabilizing method without additional energy consumption, high-pressure buffer tank of natural gas is arranged in parallel between natural gas booster outlet and gas turbine gas module inlet;Maximum pressure of natural gas booster outlet is the maximum gas pressure of high-pressure buffer tank of natural gas;In the process that natural gas working booster stops, standby booster starts to reach full load, high-pressure buffer tank of natural gas releases natural gas to maintain stable operation of gas turbine in switching time, and this minimum gas storage volume is minimum buffer volume;Water volume of high-pressure buffer tank of natural gas is calculated;Through buffer volume calculation, a feasible scheme for realizing the buffer volume is proposed, to ensure the stability of gas turbine inlet pressure during natural gas booster fault switching, thereby improving the economy and reliability of the entire gas-steam combined cycle power plant.

Description

Technical Field

[0001] The present invention relates to the technical field of combined cycle power plant construction, and in particular to a natural gas booster switching and voltage stabilization method without additional energy consumption. Background Art

[0002] As the primary and most critical power generation equipment in a gas-steam combined cycle power plant, gas turbines have varying requirements for the inlet pressure of the natural gas fuel. Their operational stability impacts the safety of the entire power plant's equipment and the grid. However, due to strict restrictions on natural gas pipeline transportation in some countries or regions (requiring natural gas transmission pressures to be below 1 MPa or lower) or varying transportation conditions, the natural gas supply pressure at the end of the natural gas transmission pipeline network cannot meet the operating requirements of the gas turbine. Therefore, a natural gas booster system is required to maintain the required gas pressure at the gas turbine inlet. Furthermore, the stable operation of the natural gas booster enhances the unit's ability to cope with fuel supply risks.

[0003] Natural gas boosters are typically configured with one in operation and one in standby, or two in operation and one in standby. This means that if one of the active boosters fails, the standby booster must be immediately activated to ensure normal gas supply to the gas turbine. However, it typically takes a long time (3-5 minutes) from the shutdown of the active booster to the startup of the standby booster and its full load. During this time, the gas turbine's ability to instantly reduce load is far from sufficient. The high natural gas consumption by the gas turbine and the loss of booster output can cause the natural gas pressure at the turbine inlet to drop sharply below its minimum allowable pressure, potentially causing the gas turbine to trip.

[0004] There are currently two commonly used technical solutions for switching and stabilizing the pressure of natural gas boosters.

[0005] (1) Booster hot standby solution:

[0006] The solution is to keep the standby natural gas booster in hot standby status at all times, that is, to maintain the compressed air and nitrogen consumption requirements of the standby booster; maintain the cooling water circulation of the standby compressor; maintain the oil circulation of the standby compressor; and maintain the normal operation of the cover ventilation system and sealing system of the standby compressor.

[0007] This hot standby state allows the standby booster to skip the auxiliary system startup and a series of inspection procedures during the normal startup process and start quickly, achieving a non-disruptive switchover from the natural gas booster to the gas turbine;

[0008] However, this solution requires the backup natural gas booster to be kept in hot standby mode at all times, which consumes a large amount of compressed air, nitrogen, and cooling water, and the operation of its auxiliary systems also increases electricity consumption.

[0009] (2) Compression buffer tank solution:

[0010] The solution is to add at least one buffer branch containing a small natural gas booster (reciprocating natural gas booster), a natural gas compression buffer tank group (gas storage pressure 7-8MPa), a pressure reducing valve and an electric heater in the pipeline from the outlet of the natural gas booster unit to the gas turbine front module, providing sufficient capacity of buffer natural gas to effectively prevent the risk of gas turbine load reduction or even tripping during the switching of the natural gas booster, thereby ensuring the safe operation of the unit.

[0011] For example, a Chinese patent published on November 3, 2023, with patent publication number CN114320493B, discloses a method for disturbance-free switching between booster units of a 9H-class combined cycle unit. The method uses the lowest value of the natural gas pressure range at the inlet of the gas turbine fuel module, or a pressure condition lower than the lowest value, to reversely infer the minimum allowable pressure at the outlet of the booster, and calculates the minimum buffer volume under the corresponding conditions. The calculated minimum buffer volume is then optimized and reduced; and an implementation scheme for setting the buffer volume based on the optimized buffer volume is provided.

[0012] Before starting the gas turbine, the natural gas compression buffer tank is pre-charged by an additional reciprocating natural gas booster, so that the natural gas pressure in the compression buffer tank reaches the set gas storage pressure (7-8MPa) to complete the charging process;

[0013] However, since the natural gas pressure requirement at the gas module inlet of gas turbines (F-class and H-class) is generally 3-4.5 MPa, the high-pressure natural gas delivered from the natural gas compression buffer tank must be regulated by a pressure reducing valve group before entering the gas turbine. As the natural gas pressure drops, its temperature generally decreases. Therefore, an electric heater is installed upstream of the pressure reducing valve group to meet the gas turbine performance heater natural gas inlet temperature requirements.

[0014] The system required both conventional large-scale booster units and reciprocating boosters for the buffer tanks. Furthermore, an electric heater for the buffer tank outlet was required. This not only increased the complexity of the entire natural gas system but also increased the project's investment costs. The filling and deflation of the buffer tanks also incurred significant additional electricity consumption. Summary of the Invention

[0015] In view of the deficiencies of the prior art, the present invention provides a natural gas booster switching and voltage stabilization method and a construction method without additional energy consumption to solve the above problems.

[0016] The present invention provides the following technical solutions:

[0017] A method for switching and stabilizing the pressure of a natural gas booster without extra energy consumption comprises the following steps:

[0018] A natural gas high-pressure buffer tank is provided in parallel between the outlet of the natural gas booster and the inlet of the gas module of the gas turbine;

[0019] Clarify the natural gas pressure requirements at the inlet of the gas turbine gas module and the maximum pressure at the outlet of the natural gas booster;

[0020] The maximum pressure at the outlet of the natural gas booster is the maximum filling pressure of the natural gas high-pressure buffer tank;

[0021] When the natural gas working booster is shut down and the standby booster is started up to full load, the natural gas high-pressure buffer tank releases natural gas to maintain stable operation of the gas turbine during the switching time. This minimum gas storage volume is the minimum buffer volume;

[0022] The calculation formula for buffer volume is as follows:

[0023]

[0024] Where V 缓 ——Buffer capacity of natural gas high-pressure buffer tank (Nm 3 );

[0025] V 水 ——Water volume of natural gas high-pressure buffer tank (m 3 );

[0026] Δp——Δp=10×(p1-p2);

[0027] p1——gas filling pressure of natural gas high-pressure buffer tank (MPa.g);

[0028] p2——the minimum pressure allowed at the inlet of the gas module (MPa.g);

[0029] T0——standard state temperature;

[0030] T2 - gas temperature in the natural gas high-pressure buffer tank, taken as ambient temperature;

[0031] M——mass flow rate of natural gas consumed by the gas turbine (kg / s);

[0032] t——time required for switching of natural gas booster (s);

[0033] ρ0——Natural gas density under standard conditions (kg / Nm 3 );

[0034] Calculate the water volume V of the natural gas high-pressure buffer tank required under corresponding conditions 水 .

[0035] Preferably, when the natural gas booster operates normally, the natural gas high-pressure buffer tank is inflated with the natural gas booster inlet regulating valve fully open;

[0036] When the natural gas booster needs to be switched, the natural gas high-pressure buffer tank rear isolation valve is opened to continuously provide natural gas for the gas turbine until the natural gas booster completes the switching process.

[0037] Preferably, the gas turbine has an online automatic fuel switching capability from natural gas to distillate oil, the natural gas consumption required for the gas turbine to complete the gas to oil switching is calculated to obtain the buffer volume of the natural gas high-pressure buffer tank required for fuel switching by using a buffer volume calculation formula, and the water volume V of the natural gas high-pressure buffer tank under corresponding conditions is calculated. 水 .

[0038] The present application has the following beneficial technical effects:

[0039] The natural gas high-pressure buffer tank is connected in parallel between the natural gas booster outlet and the gas turbine gas module inlet, and no additional energy consumption is required during switching, thereby reducing the power consumption rate of the entire plant.

[0040] In the case that the natural gas booster inlet regulating valve is fully open, the natural gas high-pressure buffer tank is inflated, so that the gas pressure in the natural gas high-pressure buffer tank is maintained at a certain high level, ensuring that the gas pressure in the natural gas high-pressure buffer tank is greater than the natural gas pressure at the gas turbine gas module inlet, and at the same time, it will not be too high to meet the direct use requirements, without the need for additional pressure or pressure reduction;

[0041] The minimum water volume of the high-pressure buffer tank required to achieve the above purpose is calculated by the formula, thereby facilitating the selection of the type and quantity of the high-pressure buffer tank when the plant is built;

[0042] The buffer volume calculation proposes a feasible scheme to achieve the buffer volume, ensuring the stability of the gas turbine inlet pressure during the natural gas booster fault switching process, thereby improving the economy and reliability of the entire gas-steam combined cycle power plant. In addition, the calculation of the natural gas buffer volume required during the fuel switching process of the project also verifies that the pressure stabilizing system also has the ability to achieve fuel switching without stopping the gas turbine. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is a system connection schematic diagram of the present application;

[0044] Figure 2 is a natural gas booster performance curve of the present application;

[0045] Figure 3 is a gas turbine gas-oil fuel switching curve of the present application.

[0046] 1- High-pressure natural gas buffer tank; 2- Outlet pneumatic shut-off ball valve; 3- Inlet pneumatic shut-off ball valve; 4- Outlet pneumatic regulating valve; 6- Check valve; 10- Booster pneumatic switching valve; 11- Buffer tank pneumatic switching valve. DETAILED DESCRIPTION

[0047] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0048] like Figures 1-2 As shown:

[0049] Example: Take the 3x100% capacity natural gas booster units of an H-class gas turbine project as an example:

[0050] The natural gas boosters are configured with two in operation and one in standby mode. Each booster's 100% capacity corresponds to the fuel consumption of one gas turbine. For example, booster #1 corresponds to gas turbine #1, booster #2 corresponds to gas turbine #2, and booster #3 serves as a backup. The three boosters are connected in parallel using branches. Each booster branch is equipped with an inlet safety shut-off valve, an inlet regulating valve, an outlet check valve, an outlet regulating valve, and front and rear safety valves. The safety shut-off valve is used for safe shut-off during startup and shutdown of the booster. The regulating valve controls the natural gas pressure at the booster's inlet and outlet. The safety valve protects the booster and downstream pipeline system. A pneumatic switching valve is also installed between the outlets of the three booster branches.

[0051] Mitsubishi Heavy Industries' M701JAC gas turbine inlet has certain requirements for the range and fluctuation of natural gas pressure. If the pressure is lower than the minimum value or the pressure fluctuation rate exceeds a certain range, the gas turbine will trip. There are also requirements for the temperature upstream of the gas turbine performance heater, as follows:

[0052] 1) Natural gas pressure range at the inlet of the gas turbine gas module: 3.57~4.51MPa.g; transient: the maximum allowable pressure change rate is less than 0.08MPa / sec.

[0053] 2) Gas turbine performance heater inlet natural gas temperature requirement: ≥15℃.

[0054] 3) Natural gas consumption requirement for 100% performance guarantee: 86.4 ton / hr (24 kg / sec).

[0055] When the running 1 natural gas booster accident shutdown, will chain start standby natural gas booster. If standby natural gas booster from cold start to full load, it takes about 3-5 minutes. Considering the natural gas booster outlet to the gas turbine room of the plant site natural gas pipeline (DN400) length of about 160 m, the volume of the pipeline is about 20 m 3 , the equivalent of natural gas is only 500 kg (70℃, 4.51MPa.g), the pipeline will be consumed in 20 seconds, the gas turbine inlet natural gas pressure sharply reduced will trigger the gas turbine trip protection program.

[0056] In #1, #2, #3 natural gas booster outlet switching branch and #1, #2 gas turbine pre module (gas module inlet) are parallelly connected as needed between a number of natural gas high pressure buffer tank.

[0057] In gas turbine before the start of the high pressure natural gas buffer tank 1 downstream outlet pneumatic ball valve 2 closed state, then open the high pressure natural gas buffer tank 1 inlet pipeline on the inlet pneumatic ball valve 3 and any booster pneumatic switch valve 10, by starting the natural gas booster to maintain the gas turbine normal operation state at the same time also to the high pressure natural gas buffer tank 1 charging, adjust the natural gas booster outlet pressure to reach the natural gas booster performance curve of the highest pressure value after the chain closing high pressure natural gas buffer tank 1 inlet pipeline on the inlet pneumatic ball valve 3 complete the charging process, at this time all high pressure natural gas buffer tank 1 into the standby state ready for use;

[0058] When the gas turbine is running, if the running of #1 or #2 natural gas booster fails to shut down, the standby #3 natural gas booster and the high pressure natural gas buffer tank 1 downstream outlet pneumatic ball valve 2, outlet pneumatic regulating valve 4 and the buffer tank pneumatic switch valve 11 on the fault side are opened in chain, and the high pressure natural gas buffer tank 1 is used to supply gas to the gas turbine, so as to ensure that the natural gas pressure at the gas turbine inlet is maintained above the minimum allowable pressure before the standby #3 natural gas booster is put into use, thereby ensuring the normal and stable operation of the gas turbine and avoiding chain trip accidents; when the standby #3 natural gas booster is put into normal operation, the outlet pneumatic ball valve 2 and the outlet pneumatic regulating valve 4 downstream of the high pressure natural gas buffer tank 1 are closed, and the high pressure natural gas buffer tank 1 is recharged and enters the standby state.

[0059] The charging pressure of the high pressure natural gas buffer tank 1 is determined by the highest pressure point of the natural gas booster performance curve; the water volume of the high pressure natural gas buffer tank 1 is finally determined by the starting time of the standby natural gas booster, the gas turbine gas consumption per unit time, the charging pressure of the high pressure natural gas buffer tank 1, and the minimum allowable natural gas pressure at the gas turbine inlet.

[0060] As Figure 2The figure shows the performance curve of a natural gas booster for a project. When the inlet regulating valve of the natural gas booster is fully open, the maximum pressure at the outlet of the natural gas booster under partial load conditions is 5.35 MPa.g, that is, the maximum achievable inflation pressure of the natural gas high-pressure buffer tank 1 is 5.35 MPa.g.

[0061] During the process of shutting down the active natural gas booster and starting up the standby booster, the natural gas operating pressure in the pipeline continuously decreases until it reaches the minimum allowable natural gas pressure at the gas turbine inlet. At this point, the standby booster starts up, reaches full load, and is put into operation, enabling stable switching of the natural gas booster. Given a certain storage volume of natural gas high-pressure buffer tank 1, this pressure drop allows the tank to release natural gas and maintain stable operation of the gas turbine during the switching period. This storage volume is referred to as the buffer volume.

[0062] The calculation formula for buffer volume is as follows:

[0063]

[0064] Where V 缓 ——Buffer capacity of natural gas high-pressure buffer tank (Nm 3 );

[0065] V 水 ——Water volume of natural gas high-pressure buffer tank (m 3 );

[0066] Δp——Δp=10×(p1-p2);

[0067] p1——natural gas high-pressure buffer charging pressure (MPa.g);

[0068] p2——the minimum pressure allowed at the inlet of the gas module (MPa.g);

[0069] T0——standard state temperature, T0=273K;

[0070] T2 - gas temperature in the natural gas high-pressure buffer tank, taking the ambient temperature as T2 = 293K;

[0071] M - mass flow rate of natural gas consumed by the gas turbine (kg / s);

[0072] t——time required for switching of natural gas booster (s);

[0073] ρ0——Natural gas density under standard conditions (kg / Nm 3 ).

[0074] According to the data of the M701JAC gas turbine, M = 24 kg / s; the physical property parameters of the natural gas are ρ0 = 0.8385 kg / Nm 3 ; the time for switching the natural gas booster is temporarily considered as 180 s; p1 = 5.35 MPa.g; p2 = 3.57 MPa.g;

[0075] Therefore, the calculated buffer volume V 缓 = 5152 Nm 3 ; and the water volume V 水 = 310.7 m 3 of the natural gas high-pressure buffer tank to be set can be further obtained.

[0076] The natural gas high-pressure buffer tank 1 is a pressure vessel, and a cylindrical storage tank with a single-tank water volume of 10 m 3 is selected. Considering several maintenance standby storage tanks, the final buffer volume implementation method for this project is: 35 groups of high-pressure buffer tanks, and the effective water volume of a single tank is 10 m 3 .

[0077] If there is a special requirement for the non-stop fuel conversion capacity of the gas turbine, each gas turbine has the online automatic fuel switching capability from natural gas to distillate oil when the natural gas supply is suddenly interrupted, and the gas turbine must remain stable during the switching process without stopping or tripping. According to the fuel switching curve of the gas turbine, as shown in Figure 3 , the natural gas consumption required for the gas turbine to complete the gas-oil switching after suddenly losing the natural gas supply is 3470 kg, and the natural gas buffer volume required to meet the fuel switching can be further obtained according to the buffer volume calculation formula, which is 4139 Nm 3 . This calculated value meets the buffer volume required for the booster accident switching, and therefore, the natural gas high-pressure buffer system can also meet the demand of the gas turbine fuel switching.

[0078] The above-described embodiments only express the specific implementation of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application.

Claims

1. A natural gas booster switching and voltage stabilization method without extra energy consumption, characterized in that: The following steps are involved: A natural gas high-pressure buffer tank is provided in parallel between the outlet of the natural gas booster and the inlet of the gas module of the gas turbine; Clarify the natural gas pressure requirements at the inlet of the gas turbine gas module and the maximum pressure at the outlet of the natural gas booster; The maximum pressure at the outlet of the natural gas booster is the maximum filling pressure of the natural gas high-pressure buffer tank; When the natural gas working booster is shut down and the standby booster is started up to full load, the natural gas high-pressure buffer tank releases natural gas to maintain stable operation of the gas turbine during the switching time. This minimum gas storage volume is the minimum buffer volume; The calculation formula for buffer volume is as follows: Where V 缓 ——Buffer volume of natural gas high-pressure buffer tank, in Nm 3 ; V 水 ——Water volume of natural gas high-pressure buffer tank, unit: m 3 ; Δp——Δp=10×(p1-p2); p1——the filling pressure of the natural gas high-pressure buffer tank, in MPa.g; p2——the minimum pressure allowed at the inlet of the gas module, in MPa.g; T0——standard state temperature; T2 - gas temperature in the natural gas high-pressure buffer tank, taken as ambient temperature; M——mass flow rate of natural gas consumed by the gas turbine, in kg / s; t——the time required for the natural gas booster to switch, in seconds; ρ0——density of natural gas under standard conditions, unit is kg / Nm 3 ; Calculate the water volume V of the natural gas high-pressure buffer tank required under corresponding conditions 水 .

2. A natural gas booster switching and voltage stabilization method without extra energy consumption according to claim 1, characterized in that: When the natural gas booster operates normally, the natural gas high-pressure buffer tank is inflated with the natural gas booster inlet regulating valve fully open; When the natural gas booster needs to be switched, the isolation valve behind the natural gas high-pressure buffer tank opens to continue supplying natural gas to the gas turbine until the natural gas booster completes the switching process.

3. A natural gas booster switching and voltage stabilization method without extra energy consumption according to claim 1, characterized in that: The gas turbine has the ability to automatically switch fuel from natural gas to distillate oil online. The natural gas consumption required by the gas turbine to complete the gas-to-oil switch is combined with the buffer volume calculation formula to obtain the buffer volume of the natural gas high-pressure buffer tank required to meet the fuel switching. The water volume V of the natural gas high-pressure buffer tank under the corresponding conditions is calculated. 水 .

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