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CN-121993775-A - Methanol-natural gas dual-fuel collaborative combustion system and method

CN121993775ACN 121993775 ACN121993775 ACN 121993775ACN-121993775-A

Abstract

The invention provides a methanol-natural gas dual-fuel collaborative combustion system and a method thereof, wherein the methanol-natural gas dual-fuel collaborative combustion system comprises a dual-fuel supply subsystem, a cyclone burner group, a heating surface collaborative subsystem, a flue gas purification and induced air subsystem and a DCS closed loop control subsystem, and has the beneficial effects that the collaborative optimization of main steam temperature elevation and carbon emission reduction is realized And the emission realizes the unification of high-efficiency operation and low-carbon emission.

Inventors

  • YAN ZHENRONG
  • GAO XIANGKAI
  • WANG LI

Assignees

  • 上海工程技术大学

Dates

Publication Date
20260508
Application Date
20260106

Claims (10)

  1. 1. The methanol-natural gas dual-fuel collaborative combustion system is characterized by comprising a dual-fuel supply subsystem, a cyclone burner group, a heating surface collaborative subsystem, a flue gas purification and induced air subsystem and a DCS closed-loop control subsystem; the dual fuel supply subsystem comprises a natural gas supply branch and a methanol supply branch which are mutually independent; the cyclone burner group comprises at least two natural gas burners and at least one methanol burner, and the methanol burner and the natural gas burner are arranged in a hearth space in a grading manner; The heating surface cooperative subsystem comprises a screen superheater, a high-temperature superheater, a low-temperature superheater, an economizer and an air preheater which are sequentially arranged along the flue gas flow; the smoke purification and induced air subsystem comprises an induced draft fan, a dust remover and a chimney; The DCS closed loop control subsystem is configured to execute a multivariable decoupling control strategy, takes the main steam temperature as a core regulated quantity, takes the mass flow ratio of methanol to natural gas as a key control quantity, and takes the hearth outlet oxygen quantity, NOx concentration and NOx concentration as a key control quantity Concentration was used as a constraint.
  2. 2. The methanol-natural gas dual fuel co-combustion system of claim 1, wherein the natural gas supply branch comprises a main gas main pipe and an ignition gas main pipe led from a plant natural gas pipeline, the main gas main pipe and the ignition gas main pipe are respectively connected to each natural gas burner through a plurality of independent branches, the main gas main pipe and the ignition gas main pipe are respectively provided with a dual redundant pneumatic quick-cut valve hard-wired with a Main Fuel Trip (MFT) system, the methanol supply branch comprises a methanol storage tank, a delivery pump and an atomization device which are sequentially connected, the methanol storage tank is provided with a nitrogen sealing device and a heating device, a self-operated reflux regulating valve is arranged at an outlet of the delivery pump, and the atomization device is a pressure atomization nozzle or a double fluid atomization nozzle.
  3. 3. The dual fuel co-combustion system of methanol-natural gas of claim 2, wherein the methanol supply branch further comprises an adaptation module, the adaptation module is a caustic scrubber at an outlet of the methanol storage tank when the water content of the methanol fuel exceeds a preset threshold, the heating device is replaced with a steam coil heat tracing when the ambient temperature is below the preset threshold, and the atomizing device is replaced with a steam-methanol dual fluid atomizing nozzle.
  4. 4. The methanol-natural gas dual-fuel collaborative combustion system according to claim 1, wherein the methanol burner is arranged at the middle upper part of the two side furnace walls of a boiler, the natural gas burner is intensively arranged at the middle lower part of the front wall of the boiler, the methanol burner adopts a double-cyclone coupling structure and comprises adjustable axial cyclone blades and radial cyclone blades, the adjustable axial cyclone blades and the radial cyclone blades are used for premixing methanol and air at the downstream of a nozzle, the air distribution system carries out three-stage hierarchical air supply, and the three-stage hierarchical air supply comprises primary air sent to the root of a methanol flame, secondary air used for organizing natural gas combustion and tertiary air introduced from the bottom of a hearth and used for reducing the peak temperature of the flame.
  5. 5. The methanol-natural gas dual-fuel co-combustion system according to claim 1, wherein the economizer adopts a two-stage arrangement, comprises an upper-stage economizer positioned below the low-temperature superheater and a lower-stage economizer positioned above the air preheater, and the screen superheater adopts an H-shaped fin tube structure, and the radiation absorption characteristic of the screen superheater is matched with the radiation spectrum of methanol flame.
  6. 6. The methanol-natural gas dual-fuel collaborative combustion system according to claim 1, wherein the induced draft fan is driven by a permanent magnet synchronous variable frequency motor, the dust remover is a bag-type dust remover or an electric bag composite dust remover, and a chimney outlet is used for monitoring On-line monitoring device for NOx and smoke concentration.
  7. 7. The methanol-natural gas dual-fuel co-combustion system of claim 6, wherein the flue gas cleaning and induced air subsystem further comprises an SCR denitration device, the SCR denitration device being disposed after the air preheater.
  8. 8. The methanol-natural gas dual fuel co-combustion system of claim 1, wherein the control algorithm executed by the DCS closed loop control subsystem comprises: the feedforward control unit calculates the theoretical demand of methanol and natural gas according to the boiler load instruction; The closed loop feedback unit takes the temperature deviation of the main steam as input, adjusts the flow of the methanol through the PID controller and adjusts the natural gas flow in parallel; constraint regulation unit for preferentially regulating combustion air distribution when NOx concentration exceeds standard And when the emission exceeds the standard, the methanol blending combustion proportion is preferentially improved.
  9. 9. The methanol-natural gas dual fuel co-combustion system of claim 8, wherein the DCS closed loop control subsystem further comprises a safety interlock unit that includes a receive MFT signal and trigger an interlock shut off of a valve and a methanol feed pump and a flame detection signal based on a "two out of three" logic to trigger a shut off of a single burner fuel valve.
  10. 10. A method of operating a methanol-natural gas dual fuel co-combustion system as in any one of claims 1-9, comprising the steps of: The method comprises the steps of 1, cold starting, igniting by using natural gas, starting methanol supply after the temperature of a hearth is increased to a set value, and slowly increasing the methanol blending combustion proportion from an initial value according to a set slope; Step 2, variable load operation, wherein in the load lifting process, the methanol mixing and burning proportion is correspondingly increased when the load is increased by a certain proportion, and in the load reducing process, the methanol mixing and burning proportion is correspondingly reduced when the load is reduced by a certain proportion, and the upper limit of the methanol mixing and burning proportion is limited when the load is reduced; step 3, normally stopping, firstly reducing the methanol blending combustion proportion to zero, purging a methanol pipeline, cutting off the natural gas supply, and executing furnace purging; and 4, emergency treatment, namely immediately stopping methanol supply and purging inert gas when methanol leakage occurs, and triggering the MFT and cutting off all fuel supply when fire extinguishment occurs.

Description

Methanol-natural gas dual-fuel collaborative combustion system and method Technical Field The invention relates to the technical field of low-carbon coupled combustion of power station boilers, in particular to a methanol-natural gas dual-fuel collaborative combustion system and method. Background In practice, some research and practice has explored the combustion characteristics of methanol in boilers. For example, there are studies on the combustion characteristics of a methanol boiler by means of numerical simulation and experimental verification, and further analysis is conducted on the influence of factors such as different excess air coefficients, different pyrolysis gas blending ratios and the like on the combustion and emission characteristics of the boiler (Zeng Mingtao. Study on the characteristics of methanol for combustion in a boiler and pyrolysis gas thereof [ D ]. Wuhan: university of science and technology, 2021). In addition, some areas are also used for exploring the application of the methanol fuel in the heat supply boiler, especially in northern areas, the methanol boiler has important significance in replacing scattered coal and reducing environmental pollution due to large heat supply requirements. However, there is relatively little research currently directed to systems and methods for co-firing methanol in a gas fired boiler to raise the main steam temperature and achieve synergistic carbon reduction. In the prior art, although some researches relate to the combustion of methanol in boilers, most focus on the combustion characteristics of single fuel or the application of small boilers, and further exploration and innovation are still needed for how to effectively mix-burn methanol in large gas boilers to achieve the increase of the temperature of main steam and the reduction of carbon emission at the same time. Therefore, the development of the combustion system and the method for the methanol co-combustion of the gas boiler, which can meet the requirements, has important practical significance for promoting the development of the low-carbon coupling combustion technology of the power station boiler. The prior art explores to some extent the use of methanol in combustion systems, but they focus mainly on the engine or coal-fired boiler field, unlike the present invention which aims at the goal and technological path of co-firing methanol in a gas-fired boiler to raise the main steam temperature and co-operate with carbon reduction. Disclosure of Invention In order to overcome the problems in the prior art, the invention provides a methanol-natural gas dual-fuel collaborative combustion system and a method. The invention discloses a methanol-natural gas dual-fuel collaborative combustion system, which comprises a dual-fuel supply subsystem, a cyclone burner group, a heating surface collaborative subsystem, a flue gas purification and induced air subsystem and a DCS closed-loop control subsystem, wherein the dual-fuel supply subsystem comprises a natural gas supply branch and a methanol supply branch which are mutually independent, the cyclone burner group comprises at least two natural gas burners and at least one methanol burner, the methanol burner and the natural gas burner are distributed in a hearth space in a grading manner, the heating surface collaborative subsystem comprises a screen type superheater, a high-temperature superheater, a low-temperature superheater, a coal economizer and an air preheater which are sequentially distributed along a flue gas flow path, the flue gas purification and induced air subsystem comprises an induced draft fan, a dust remover and a chimney, the DCS closed-loop control subsystem is configured to execute a multivariable decoupling control strategy, the temperature of main steam is used as a core regulated quantity, the mass flow ratio of methanol and natural gas is used as a key control quantity, and the hearth outlet oxygen quantity, NOx concentration and air preheater are used for controlling the hearth outlet quantityConcentration was used as a constraint. On the basis, the natural gas supply branch comprises a main gas main pipe and an ignition gas main pipe which are led from a plant natural gas pipeline, the main gas main pipe is respectively connected to each natural gas burner through a plurality of independent branches, the main gas main pipe and the ignition gas main pipe are respectively provided with a double-redundancy pneumatic quick-cutting valve which is hard-wired with a Main Fuel Trip (MFT) system, the methanol supply branch comprises a methanol storage tank, a delivery pump and an atomizing device which are sequentially connected, the methanol storage tank is provided with a nitrogen sealing device and a heating device, a self-operated reflux regulating valve is arranged at an outlet of the delivery pump, and the atomizing device is a pressure atomizing nozzle or a double-fluid atomizing nozzle. On the basis, the methanol