CN-122020236-A - Method for replacing natural gas by dynamically conditioning hydrogen-rich tail gas as byproduct of PDH device

CN122020236ACN 122020236 ACN122020236 ACN 122020236ACN-122020236-A

Abstract

The invention provides a method for dynamically modifying and replacing natural gas by byproduct hydrogen-rich tail gas of a PDH device, which comprises the following steps of S1, setting a standard Hua Bai number of target substitute natural gas and a safe combustion potential threshold value, S2, collecting flow and component data of a first flow in a hydrogen-rich gas pipeline and component data of a second flow in a carbon two tail gas pipeline in real time, reversely calculating theoretical target flow of the second flow, S3, predicting synthetic combustion potential of mixed gas, comparing the synthetic combustion potential with the safe combustion potential threshold value, triggering intervention and adjustment if the synthetic combustion potential exceeds the threshold value, generating a flow adjustment instruction if the synthetic combustion potential exceeds the threshold value, S4, adjusting the flow of the second flow, monitoring actually measured Hua Bai number of output mixed gas in real time, and compensating and adjusting the flow of the second flow through a feedback compensation algorithm. The invention converts the hydrogen-rich dry gas and the carbon two tail gas with severe component fluctuation and great combustion characteristic difference into the high-quality fuel gas which completely targets the industrial natural gas on the aspect of combustion interchangeability.

Inventors

NI YONGZHI
FANG GUOQING
GAO YILIANG
ZHOU XIANG
JIA XUDONG
JIANG YIDONG
JIAO ZHENHUA
DENG SHASHA
DONG YAHUI
HU JINYANG

Assignees

浙江华泓新材料有限公司

Dates

Publication Date: 20260512
Application Date: 20251215

Claims (8)

1. The method for replacing natural gas by dynamically conditioning hydrogen-rich tail gas of a PDH device is performed based on a dynamic conditioning proportioning system, the dynamic conditioning proportioning system comprises a raw material pretreatment unit, a dynamic mixing unit, a buffer homogenizing unit, an on-line monitoring feedback unit and a control unit, and the raw material pretreatment unit is respectively connected with a hydrogen-rich dry gas pipeline and a carbon two tail gas pipeline, and is characterized by comprising the following steps: S1, setting a reference, namely setting a reference Hua Bai number of target substitute natural gas and a safe combustion potential threshold value in a control unit; S2, feedforward calculation, namely collecting flow and component data of a first flow in a hydrogen-rich dry gas pipeline and component data of a second flow in a carbon two tail gas pipeline in real time, and reversely calculating theoretical target flow of the second flow by using a heat value balance model based on the reference Hua Bai; S3, safety constraint checking, namely predicting the synthetic combustion potential of the mixed gas according to the flow of the first flow and the theoretical target flow of the second flow, comparing the synthetic combustion potential with the safety combustion potential threshold, triggering intervention and adjustment if the synthetic combustion potential exceeds the threshold, and generating a flow adjustment instruction if the synthetic combustion potential does not exceed the threshold; And S4, executing, namely regulating the flow of the second flow according to the flow regulating instruction, enabling two gases of the first flow and the second flow to enter the dynamic mixing unit for mixing, stabilizing the pressure by the buffer homogenizing unit and then outputting the mixture, monitoring the actual measured Hua Bai number of the output mixed gas in real time, calculating the deviation between the actual measured Hua Bai number and the reference Hua Bai number, and carrying out compensation regulation on the flow of the second flow through a feedback compensation algorithm.
2. The method for dynamically conditioning and replacing natural gas by-product hydrogen-rich tail gas of a PDH device according to claim 1, wherein in the step S2, the control unit calculates the theoretical target flow QB of the second flow based on the following white number coupling formula: In the formula, For the target natural gas replacement benchmark Hua Bai, QA is the real-time flow of the first stream, LHVA is the lower heating value of the first stream, LHVB is the lower heating value of the second stream, dA is the relative density of the first stream, and dB is the relative density of the second stream.
3. The method for dynamically conditioning and replacing natural gas by-product hydrogen-rich tail gas of a PDH device according to claim 1, wherein in the step S3, the intervention and adjustment specifically comprises: when the calculated synthetic combustion potential is greater than the safe combustion potential threshold, the control unit enforces a hydrogen reduction strategy including limiting flow input to the first flow stream until the recalculated synthetic combustion potential is less than the safe combustion potential threshold.
4. The method for dynamically conditioning hydrogen-rich tail gas as set forth in claim 1, wherein in the step S4, the feedback compensation algorithm adopts PID control logic, the control unit calculates a correction amount u (t) according to the deviation between the actually measured Hua Bai number and the reference Hua Bai number, and the correction amount is added to the flow adjustment command generated in the step S2, and the calculation formula of the correction amount u (t) is as follows: Where E (t) is the real-time deviation of the reference Hua Bai number from the measured Hua Bai number, kp is the proportionality coefficient, ki is the integral coefficient, and Kd is the differential coefficient.
5. The method for dynamically conditioning and replacing natural gas by-product hydrogen-rich tail gas of a PDH device according to claim 1, wherein the dynamic mixing unit comprises a Venturi jet mixer and a static mixer which are sequentially arranged along the gas flow direction, the first flow is used as injection fluid to enter the Venturi jet mixer, the second flow is used as sucked fluid to enter a suction chamber of the Venturi jet mixer, and the two flows are subjected to secondary shearing mixing after being primarily mixed at a throat pipe of the Venturi jet mixer.
6. The method for dynamically conditioning and replacing natural gas by-product hydrogen-rich tail gas of a PDH device according to claim 1, wherein the buffer homogenizing unit comprises a buffer tank, a baffle plate is arranged inside the buffer tank, and the volume of the buffer tank is configured so that the average residence time of the mixed gas in the tank is kept between 30 seconds and 60 seconds.
7. The method for dynamically conditioning and replacing natural gas by-product hydrogen-rich tail gas of a PDH device according to claim 1, wherein the first stream is hydrogen-rich dry gas from a cold box and a PSA unit of the propane dehydrogenation device, the hydrogen volume content is 40-90%, the average molecular weight is 3-10, the second stream is carbon two tail gas from a deethanizer top of the propane dehydrogenation device, the total volume content of ethane and ethylene is 80-95%, and the average molecular weight is 26-30.
8. The method for dynamically conditioning and replacing natural gas by-product hydrogen-rich tail gas of a PDH device according to claim 1, wherein the reference Hua Bai number range of the target replacement natural gas set in the step S1 is 46.5-50MJ/Nm 3 .

Description

Method for replacing natural gas by dynamically conditioning hydrogen-rich tail gas as byproduct of PDH device Technical Field The invention belongs to the technical field of petrochemical waste gas resource utilization, and particularly relates to a method for dynamically conditioning and replacing natural gas by byproduct hydrogen-rich tail gas of a PDH device. Background The Propane Dehydrogenation (PDH) process is an important route to propylene, which produces a large amount of by-product gas during production. The method mainly comprises two streams, namely a hydrogen-rich dry gas from a cold box and a pressure swing adsorption unit, wherein the hydrogen content is high, usually more than 40%, the molecular weight is extremely small and is about 3-10, and a carbon two tail gas from the top of the deethanizer, mainly comprising ethane and ethylene, and the main components are high in heat value and relatively large in molecular weight and are about 26-30. The treatment mode of the byproduct gas in the prior art mainly adopts the flare burning emission, which not only causes the waste of hydrogen heat value energy, but also increases the emission of pollutants such as CO 2, NOx and the like, and does not meet the double-carbon target. Another treatment method is to use the fuel as a low-grade fuel for simple boiler heating, but the high value thereof cannot be exerted. There are also attempts to mix two gases and send the mixed gases into a natural gas pipe network to replace natural gas, but when the gas is replaced by the byproduct gas to supply gas to a downstream heating furnace, the flow and components of the hydrogen-rich dry gas can be periodically and severely fluctuated when the adsorption/analysis are switched by a pressure swing adsorption unit of a PDH device, so that the stability of the white number of the mixed gas cannot be ensured due to simple physical mixing, and the fluctuation of the white number can cause the fluctuation of the heat load of the downstream heating furnace to influence the product quality. And the burning speed of the hydrogen is 7-8 times that of the methane, if only the matching of the heat values is considered and the control of the burning potential is ignored, when the hydrogen content in the mixed gas is too high, the situation that the flame propagation speed is higher than the air flow speed easily occurs in a non-special burner, and the burner nozzle is burnt due to tempering. In addition, conventional PID feedback control is difficult to cope with frequent changes in feed gas composition, resulting in a lag in regulation, which cannot meet the stringent requirements of industrial parks on gas quality. Disclosure of Invention Based on the background, the invention aims to provide a method for dynamically conditioning and replacing natural gas by byproduct hydrogen-rich tail gas of a PDH device, which realizes complementation of high-hydrogen low-carbon dry gas and high-carbon high-heat value tail gas by double control of Hua Bai numbers and combustion potential and solves the technical problems of unstable combustion and easy tempering caused by simply mixing and utilizing the hydrogen-rich dry gas and the carbon two tail gas in the prior art. In order to achieve the above object, the present invention provides the following technical solutions: the method for replacing natural gas by dynamically conditioning hydrogen-rich tail gas of a PDH device is performed based on a dynamic conditioning proportioning system, the dynamic conditioning proportioning system comprises a raw material pretreatment unit, a dynamic mixing unit, a buffering homogenizing unit, an on-line monitoring feedback unit and a control unit, the raw material pretreatment unit is respectively connected with a hydrogen-rich dry gas pipeline and a carbon two tail gas pipeline, and the method comprises the following steps: S1, setting a reference, namely setting a reference Hua Bai number of target substitute natural gas and a safe combustion potential threshold value in a control unit; S2, feedforward calculation, namely collecting flow and component data of a first flow in a hydrogen-rich dry gas pipeline and component data of a second flow in a carbon two tail gas pipeline in real time, and reversely calculating theoretical target flow of the second flow by using a heat value balance model based on the reference Hua Bai; S3, safety constraint checking, namely predicting the synthetic combustion potential of the mixed gas according to the flow of the first flow and the theoretical target flow of the second flow, comparing the synthetic combustion potential with the safety combustion potential threshold, triggering intervention and adjustment if the synthetic combustion potential exceeds the threshold, and generating a flow adjustment instruction if the synthetic combustion potential does not exceed the threshold; And S4, executing, namely regulating the flow of the second flow according to th