LNG dual-fuel ship exhaust monitoring device

Abstract

The utility model relates to gas detection technical field, the utility model provides a kind of LNG dual-fuel ship exhaust monitoring device, using ultraviolet differential absorption, non-dispersed infrared absorption and tunable semiconductor laser absorption spectroscopy etc. Optical detection principle realizes the synchronous detection of four kinds of gases SO2 (0~1500ppm), CO2 (0~30%), CH4 (0~1500ppm) and NO (0~1500ppm), error is controlled within ±2%FS, response time is not more than 30s. Realize LNG dual-fuel characteristic gas accurate detection simultaneously, with the advantages of high detection precision, fast response speed, simple operation, relatively low cost and strong gas cross-interference resistance ability under complex working conditions.

Description

Technical Field

[0001] This utility model relates to the field of gas detection technology, specifically to an LNG dual-fuel ship exhaust gas monitoring device. Background Technology

[0002] Ships, as vital transportation tools, facilitate global trade and passenger transport, but their engines generate significant exhaust emissions during operation. Currently, international organizations such as the International Maritime Organization have established a series of ship emission standards and safety regulations. Strict ship exhaust emission standards require the use of more environmentally friendly technologies and equipment to reduce emissions. LNG (liquefied natural gas), as a clean, efficient, and easily transportable alternative to fossil fuels, not only meets the urgent global demand for energy security and supply diversification but also plays a crucial role in the energy transition. LNG-fueled ships offer numerous advantages, including significant environmental benefits, high technological maturity, substantial economic benefits, low operating costs, and broad application prospects. LNG dual-fuel ships typically use LNG and diesel as fuel, and their exhaust emissions mainly include carbon dioxide, nitrogen oxides, sulfur oxides, and unburned methane, with CO2, NO, SO2, and CH4 being the most prominent components.

[0003] Accurate measurement of the concentration of each component in exhaust gas is a crucial prerequisite for exhaust gas treatment and control. Only by promptly understanding changes in exhaust gas concentration can targeted countermeasures be taken as quickly as possible. However, existing analyzers can only detect single or a few gas components, failing to comprehensively reflect the true situation of exhaust gas emissions. Furthermore, existing methods cannot rapidly and accurately measure the concentration of each gas component while ensuring a high measurement range.

[0004] Specifically, there are some difficulties in monitoring exhaust emissions from LNG diesel dual-fuel engines: (1) The mixed combustion of multiple fuels results in complex gas composition, requiring monitoring equipment to have multi-gas detection capabilities and to solve the problem of cross-interference between components; (2) Online real-time detection places high demands on the response speed and stability of the equipment; (3) Economic cost and technical complexity, the cost of equipment and the complexity of periodic calibration and maintenance are also important aspects that make it difficult to promote and apply the detection technology; (4) Environmental robustness, given the variability of temperature, humidity and pressure in the ship detection environment, there is a lack of scientific compensation algorithms to improve detection accuracy. Utility Model Content

[0005] In view of this, the present invention provides an LNG dual-fuel ship exhaust gas monitoring device that can achieve accurate measurement of multiple gases, has strong anti-cross interference capability and stable performance.

[0006] To achieve the above objectives, this utility model proposes an LNG dual-fuel ship exhaust gas monitoring device, which includes a power supply module, a control module, a sensor module, and a screen. The power supply module is responsible for providing power to the entire device. The control module is responsible for signal acquisition and processing, control, communication, fault diagnosis, and data storage. The sensor module includes SO2 / NO sensors, CH4 sensors, and CO2 sensors, which respectively detect the concentrations of SO2 / NO, CH4, and CO2. The screen displays and calibrates the concentrations of each gas, as well as displaying auxiliary information.

[0007] This also includes external communication interfaces, which read or configure data through established standard protocols.

[0008] The sensor module includes a temperature and humidity sensor and a flow sensor. After the control module completes the collection of concentration data from each gas sensor, it displays the relevant information on the screen. At the same time, it collects the values ​​from the temperature and humidity sensor for temperature and humidity compensation of each module, and also collects the values ​​from the flow sensor for flow monitoring.

[0009] Among them, the SO / NO sensor, based on ultraviolet differential absorption spectroscopy, is configured to detect SO concentration in the 288.5-310.0 nm band and NO concentration in the 220.7-227.2 nm band; the CO sensor, based on non-dispersive infrared absorption spectroscopy, detects CO; and the CH sensor, based on tunable semiconductor laser absorption spectroscopy, uses a 1.684 μm wavelength laser to detect CH.

[0010] The optical gas path length of the SO / NO sensor is 150 mm.

[0011] The control module performs real-time environmental compensation for each sensor using temperature and humidity sensor data.

[0012] The CH sensor uses a direct absorption method to measure gas concentration.

[0013] Beneficial effects:

[0014] 1. This utility model device employs optical detection principles such as ultraviolet differential absorption, non-dispersive infrared absorption, and tunable semiconductor laser absorption spectroscopy to achieve simultaneous detection of four gases: SO2 (0–1500 ppm), CO2 (0–30%), CH4 (0–1500 ppm), and NO (0–1500 ppm). The error is controlled within ±2%FS, and the response time does not exceed 30 seconds. It enables simultaneous and accurate detection of characteristic gases from both LNG and other fuels, offering advantages such as high detection accuracy, fast response speed, simple operation and maintenance, relatively low cost, and strong resistance to cross-interference under complex operating conditions.

[0015] 2. This utility model device outputs a standard RS485 signal and can be used for closed-loop regulation or microcomputer automatic control. It offers stable detection performance, high measurement accuracy, and strong resistance to interference from process background gases.

[0016] 3. This utility model device incorporates gas characteristics into its gas path design, which greatly improves the real-time performance and response speed of detection. Furthermore, its functional design is convenient and intelligent, with a user-friendly human-machine interface, making it easy for users to perform calibration and fault location.

[0017] 4. This utility model device has low operation and maintenance costs, long service life, and good long-term stability, thus reducing economic costs. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the LNG dual-fuel ship exhaust gas monitoring device of this utility model.

[0019] Figure 2 This is a schematic diagram of the differential cross sections of SO2 and NO gases.

[0020] Figure 3 This is a schematic diagram of the absorption spectra of CH4 and CO2 near 1.654 μm in an embodiment of the method of this utility model.

[0021] Figure 4 This is a schematic diagram of the absorption spectra of CH4 and CO2 near 1.684 μm in an embodiment of the method of this utility model. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] Analysis of the detection principles reveals that SO2 and NO can be detected using various methods. Ultraviolet absorption offers high precision but suffers from complex optical design and data processing. Electrochemical methods are suitable for portable detection but have low accuracy and short lifespan. Chemiluminescence methods offer high sensitivity but are costly and susceptible to interference from other gases. Chemiluminescence methods offer high sensitivity but have high consumable and operating costs. Non-dispersive infrared absorption technology can be used for CO2 and CH4 detection; it is a mature and cost-effective method, but it is susceptible to background gas interference, and high concentrations of carbon dioxide can affect the accuracy of methane detection. Photoacoustic spectroscopy and gas chromatography both offer high sensitivity and precision, but the equipment is complex and costly. Tunable semiconductor laser absorption spectroscopy offers high sensitivity and fast response, but it is relatively expensive.

[0024] This utility model discloses an LNG dual-fuel ship exhaust gas monitoring device that employs a composite sensor array, designed in conjunction with the detection characteristics of various characteristic gases. It includes a power supply module, a control module, a sensor module, and a screen. The power supply module is a crucial component, responsible for providing stable and reliable power to the entire device, ensuring its normal operation. The control module is the core component, responsible for signal acquisition and processing, control, communication, fault diagnosis, and data storage. The sensor module includes SO2 / NO, CH4, and CO2 sensors, respectively detecting the concentrations of SO2 / NO, CH4, and CO2. The screen displays the concentrations of each gas, performs calibration, and displays auxiliary information.

[0025] The LNG dual-fuel ship exhaust gas monitoring device of this utility model embodiment is as follows: Figure 1 As shown, it also includes an external communication interface for reading or configuring data through a defined standard protocol. The sensor module also includes a temperature and humidity sensor and a flow sensor; the control module is the main control board, which displays the data and related information on the screen after collecting the concentration data from each gas sensor; the main control board also collects the values ​​from the temperature and humidity sensor for temperature and humidity compensation of each module, and collects the values ​​from the flow sensor for flow monitoring.

[0026] In terms of gas path design, the gas to be measured passes through the inlet, where its flow rate is regulated by a float flow meter. It then sequentially enters the SO2 / NO sensor chamber, CO2 sensor chamber, CH4 sensor chamber, and flow sensor chamber before exiting through the outlet. The flow sensor monitors the gas flow rate to ensure normal gas intake for the instrument. After inversion calculation, the concentration signals of each component are sent to the main control board via serial port. The main control board then drives the screen to display the concentration data and collects fault information from each sensor. Based on the design details of each module, fault display rules are established to facilitate user monitoring of sensor status and rapid location of module faults.

[0027] This utility model discloses an exhaust gas monitoring device for LNG dual-fuel ships, which can realize real-time detection of multi-component exhaust gas components. Specifically, it employs optical detection principles such as ultraviolet differential absorption, non-dispersive infrared absorption, and tunable semiconductor laser absorption spectroscopy to simultaneously detect four gases: SO2 (0–1500 ppm), CO2 (0–30%), CH4 (0–1500 ppm), and NO (0–1500 ppm). The error is controlled within ±2%FS, and the response time does not exceed 30 seconds. This utility model device achieves simultaneous and accurate detection of characteristic gases of LNG dual-fuel ships, and has the advantages of high detection accuracy, fast response speed, simple operation and maintenance, relatively low cost, and strong resistance to cross-interference of gases under complex operating conditions.

[0028] Furthermore, this device outputs a standard RS485 signal, which can be used for closed-loop regulation or microcomputer-controlled automation. It offers stable detection performance, high measurement accuracy, and strong resistance to interference from process background gases. The device incorporates gas characteristics into its gas path design, significantly improving real-time detection and response speed. Its functional design is convenient and intelligent, with a user-friendly human-machine interface, facilitating calibration and fault location. This device boasts low maintenance costs, long lifespan, and excellent long-term stability, thus reducing economic costs.

[0029] The exhaust gas monitoring device for LNG dual-fuel ships based on this utility model ensures both large-range and high-precision detection of SO2 and NO, as well as accurate measurement of CH4 under high-concentration CO2 background, as follows:

[0030] Specifically, for the precise detection of SO2 and NO mixtures:

[0031] Differential Optical Absorption Spectroscopy (DOAS) is a highly sensitive spectroscopic analysis technique widely used in gas detection. Its core principle involves measuring the characteristic absorption differences of a target substance in the ultraviolet-visible light band, combined with mathematical algorithms to separate and analyze the spectral signals. Different gas molecules possess unique absorption "fingerprints" in the ultraviolet-visible light band; the wavelength positions, peak shapes, and intensity differences of these absorption spectra provide the physical basis for multi-component detection. The differential cross-sections of SO2 and NO are shown below. Figure 2 As shown. To achieve high-precision simultaneous detection of a large range of SO2 and NO mixed gases, the following aspects are mainly addressed:

[0032] a) Selective separation and band optimization in the ultraviolet band. Selecting appropriate inversion intervals can effectively distinguish the absorption signals of each gas and reduce cross-interference. To maximize the optimization of gas absorption characteristics and reduce redundant data processing, (288.5-310.0) nm and (220.7-227.2) nm were selected as the characteristic absorption peak bands of SO2 and NO, respectively.

[0033] (b) Considering the large measurement ranges of both gases and the large average absorption cross-section in the characteristic absorption peak band of NO, there is a possibility that the light within the absorption bandwidth will be completely absorbed (i.e., absorption saturation), leading to significant deviations in NO detection concentration. Therefore, the optical path should not be too long. Calculations show that the optical path in this embodiment is 150 mm. This optical path avoids absorption signal saturation when both gases are at high concentrations.

[0034] c) During concentration inversion calculations, after wavelet denoising, the SO2 concentration in the sample gas is first calculated using the (288.5-310.0) nm band. Then, the NO gas concentration is inverted using the absorption cross-sectional area obtained by subtracting the absorbance caused by SO2 from the (220.7-227.2) nm band. The initial concentration after inversion is calibrated using a standard gas, and a fitting curve is used to improve the detection accuracy of both gases.

[0035] Through standard gas testing, the maximum detection errors for SO2 and NO in the mixed gas were 1.44%FS and 1.89%FS, respectively. The specific test data are shown in Table 1 and Table 2.

[0036] Table 1. SO2 Standard Gas Test Data

[0037]

[0038] Table 2 NO Standard Gas Test Data

[0039]

[0040] For accurate CH4 measurement in high CO2 concentration background:

[0041] From the perspective of absorption spectral analysis, CH4 exhibits a significant absorption band near 1.654 μm, primarily corresponding to the stretching vibration of the CH bond. This band is commonly used for methane detection, while CO2 shows a strong absorption band near 4.26 μm. The absorption spectrum near 1.654 μm for 30% CO2 and a measurement range of 1500 ppm (2000:1) is shown below. Figure 3 As shown in the figure, the high concentration of CO2 near this spectral line has only a weak interference with the CH4 absorption measurement, which is almost negligible. However, in actual tests, it was found that under a background of about 30% carbon dioxide concentration, the measured CH4 value was about 150 ppm lower than the standard gas concentration. The reasons for this phenomenon are analyzed as follows:

[0042] a) In an environment where CO and CH coexist, according to the molecular collision theory, collisions between different molecules in the gas mixture will cause absorption line broadening or frequency shift. For TDLAS technology, the CH4 absorption line will be affected by collisions with CO2 molecules, resulting in a weakening of the absorption signal intensity or a frequency shift.

[0043] In one scenario, excessively high CO2 concentrations can increase the cross-broadening of the CH4 absorption line, causing the absorption line width to exceed the self-broadening of CH4. If the concentration is retrieved using second harmonic amplitude inversion, the amplitude is inversely proportional to the absorption line width. When CO2 causes the CH4 absorption line to broaden, the harmonic amplitude decreases, which may lead to changes in the amplitude of the concentration harmonic signal, resulting in inaccurate measurements. Furthermore, frequency shifts can cause the TDLAS laser wavelength to be inaccurately calibrated to the CH4 absorption peak, resulting in lower measurements.

[0044] (b) Although the main absorption peaks of CO2 and CH4 are quite different, the weak absorption band interference of CO2 on CH4 should still be considered, which may lead to deviations in the calculation of peak integration area or position, affecting the accuracy of qualitative analysis and quantitative calculation. As can be seen in the figure, CO2 has a weak absorption at 1.654 μm, which may also be one of the reasons for inaccurate CH4 concentration measurements.

[0045] c) The concentration calculation did not compensate for changes caused by broadening, and the lack of calibration for specific gas combinations led to measurement errors.

[0046] To address the above issues, the following processing method is adopted for accurate measurement of CH4 concentration under high CO2 background:

[0047] a) A 1.684 μm laser was selected for CH4 detection. Although the absorption peak here is weaker than at 1.657 μm, it is still... Figure 4 As shown, there is no CO2 absorption peak here. This fundamentally avoids the interference of CO2 on CH4 detection.

[0048] (b) Although there is no CO2 absorption near 1.684 μm as mentioned in (a), high concentrations of CO2 will cause absorption peak broadening. After signal broadening, the absorption peak value will decrease and the absorption width will increase, but the total absorbed energy will not change significantly. Therefore, the direct absorption method is used to measure CH4. Compared with the second harmonic method for measuring absorption peak height, this method directly measures the absorption area or integrated absorbance and is less affected by linewidth.

[0049] c) Design calibration data for multiple concentration ratio combinations, establish a model for curve fitting to calculate the final gas concentration. Based on the test data, establish an interference matrix and embed an algorithm for dynamic compensation.

[0050] Through standard gas testing, the maximum detection error of CH4 mixture was 1.47%FS. Specific test data are shown in Table 3.

[0051] Table 3 CH4 Standard Gas Test Data

[0052]

[0053] In summary, the above are merely preferred embodiments of this utility model and are not intended to limit the scope of protection of this utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the scope of protection of this utility model.

Claims

1. A device for monitoring exhaust gas from LNG dual-fuel ships, characterized in that, It includes a power module, a control module, a sensor module, and a screen; the power module is responsible for providing power to the entire device; the control module is responsible for signal acquisition and processing, control, communication, fault diagnosis, and data storage; the sensor module includes SO2 / NO sensors, CH4 sensors, and CO2 sensors, which respectively complete the concentration detection of SO2 / NO, CH4, and CO2; the screen displays and calibrates the concentration of each gas, as well as displaying auxiliary information.

2. The apparatus according to claim 1, characterized in that, It also includes external communication interfaces, which read or configure data through established standard protocols.

3. The apparatus according to claim 1, characterized in that, The sensor module also includes a temperature and humidity sensor and a flow sensor; after the control module completes the collection of concentration data from each gas sensor, it displays the relevant information on the screen. At the same time, it collects the values ​​from the temperature and humidity sensor for temperature and humidity compensation of each module, and also collects the values ​​from the flow sensor for flow monitoring.

4. The apparatus according to claim 2 or 3, characterized in that, The SO2 / NO sensor, based on ultraviolet differential absorption spectroscopy, is configured to detect SO2 concentration in the 288.5-310.0 nm wavelength range and NO concentration in the 220.7-227.2 nm wavelength range; the CO2 sensor detects CO2 based on non-dispersive infrared absorption spectroscopy; and the CH4 sensor detects CH4 using a 1.684 μm wavelength laser based on tunable semiconductor laser absorption spectroscopy.

5. The apparatus according to claim 4, characterized in that, The optical gas path length of the SO2 / NO sensor is 150 mm.

6. The apparatus according to claim 4, characterized in that, The control module performs real-time environmental compensation for each sensor using data from temperature and humidity sensors.

7. The apparatus according to claim 4, characterized in that, The CH4 sensor uses the direct absorption method to measure gas concentration.

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