Isooctane production waste heat cascade recycling device and control method

Abstract

The invention relates to the technical field of industrial energy conservation and waste heat recovery, in particular to an isooctane production waste heat cascade recycling device and a control method. The waste heat sensing and collecting layer is used for monitoring multi-strand waste heat source parameters in the isooctane production process in real time; the stepped conversion refining layer is connected with the waste heat sensing and collecting layer and used for carrying out stepped conversion on the waste heat according to the grade of the waste heat; through multi-stage cascade connection, each stage of working medium pair works in the most efficient temperature interval, the utilization rate of wide-range waste heat is maximized, and the loss is remarkably reduced; the system pressure can be accurately predicted and controlled, the problem of inter-stage pressure balance of a multi-stage system is solved, and stable and efficient operation of the system under various working conditions is ensured.

Description

Technical Field

[0001] This invention relates to the field of industrial energy conservation and waste heat recovery technology, specifically to a device and control method for the cascade recovery and utilization of waste heat from isooctane production. Background Technology

[0002] Petrochemical processes such as isooctane production generate a large amount of waste heat over a wide temperature range, including high-temperature flue gas (>300°C), medium-temperature process steam (100-300°C), and low-temperature cooling water (<100°C). Traditional waste heat recovery technologies, such as waste heat boilers, mainly focus on the single heat energy recovery (generating steam or hot water) of medium- and high-temperature waste heat, resulting in low utilization rates of low-temperature waste heat and a lack of tiered utilization based on waste heat grade, leading to significant energy losses. Therefore, there is an urgent need for a system that can efficiently and flexibly recover waste heat and maximize its value. Summary of the Invention

[0003] To address the problems of existing technologies, this invention provides a device and control method for the cascade recovery and utilization of waste heat from isooctane production.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A waste heat recovery and utilization device for isooctane production includes: The waste heat sensing and acquisition layer is used to monitor the parameters of multiple waste heat sources in the isooctane production process in real time. A stepped conversion and refining layer is connected to the waste heat sensing and collection layer, and is used to perform stepped conversion of waste heat according to the waste heat grade. The stepped conversion and refining layer includes at least the following: The high-temperature conversion unit is configured to convert primary waste heat into electrical energy using a supercritical carbon dioxide power cycle. The intermediate-temperature conversion unit is configured to convert the waste heat of the second grade into chemical potential energy for storage using a thermochemical adsorption reaction. The low-temperature conversion unit is configured to use a heat pump to raise the temperature of the third-grade waste heat.

[0005] The aforementioned isooctane production waste heat recovery and utilization device, wherein the medium-temperature conversion unit is a multi-stage cascaded thermochemical energy storage system, consisting of at least two adsorption energy storage modules connected in series; the first-stage adsorption energy storage module uses a first working fluid pair to process the second-grade waste heat in the higher temperature range; the second-stage adsorption energy storage module uses a second working fluid pair to process the second-grade waste heat in the lower temperature range.

[0006] The aforementioned waste heat recovery and utilization device for isooctane production has a first working fluid pair of zeolite-water and a second working fluid pair of silica gel-water; the refrigerant vapor generated by the second-stage adsorption energy storage module is fed into the refrigerant vapor pipeline generated by the first-stage adsorption energy storage module.

[0007] The aforementioned isooctane production waste heat recovery and utilization device, wherein the multi-stage cascaded thermochemical energy storage system comprises: At least two adsorption energy storage modules connected in series, each stage containing an adsorption bed and a corresponding heat exchanger; A common condenser, the inlet of which is connected to the refrigerant vapor outlet of each stage of the adsorption energy storage module; A common evaporator or liquid storage tank, the outlet of which is connected to the refrigerant inlet of each stage of adsorption energy storage module; The refrigerant vapor generated by the second-stage adsorption energy storage module is guided to merge with the refrigerant vapor generated by the first-stage adsorption energy storage module at the junction point and then enter the condenser together.

[0008] The isooctane production waste heat recovery and utilization device is provided with a Y-type tee pipe at the junction point; the outlet of the second-stage adsorption energy storage module and the outlet of the first-stage adsorption energy storage module are connected to the two inlets of the Y-type tee pipe through pipelines, and the outlet of the Y-type tee pipe is connected to the pipeline of the condenser inlet.

[0009] The isooctane production waste heat recovery and utilization device has a cascaded control high-precision regulating valve installed on the pipeline between the outlet of the second-stage adsorption energy storage module and the junction point. This valve is used to precisely control the flow rate of medium-pressure steam to the junction point in order to maintain the stability of the junction point pressure.

[0010] The control method for the isooctane production waste heat cascade recovery and utilization device includes the following steps: S1. Real-time acquisition of key system status parameters, including the temperature and pressure of each adsorption bed, and the pressure p1 at the confluence point; S2. Input the collected parameters into the mathematical model to predict the trend of system state changes within a future time window; S3. Based on the optimization objective, a series of optimal control command sequences within the future time window are obtained; S4. Execute the first instruction in the control instruction sequence and repeat steps S1-S3.

[0011] The optimization objectives include maintaining the stability of the junction point pressure p1 and maximizing the system energy storage efficiency; the control commands include at least the adjustment command for the opening of the cascaded high-precision regulating valve.

[0012] Compared with existing technologies, the beneficial effects of the invention are: by cascading multiple stages, each working fluid pair operates in its most efficient temperature range, maximizing the utilization rate of waste heat over a wide range and significantly reducing heat loss; it can accurately predict and control system pressure, solving the problem of pressure balance between stages in a multi-stage system, and ensuring the stable and efficient operation of the system under various operating conditions. Attached Figure Description

[0013] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

[0014] Figure 1 This is a schematic diagram of the overall architecture of the waste heat recovery and utilization device for isooctane production in an embodiment of the present invention. Detailed Implementation

[0015] The present invention will be further described in detail below through embodiments. These embodiments are only used to illustrate the present invention and do not limit the scope of the present invention.

[0016] A device for the cascade recovery and utilization of waste heat from isooctane production, characterized in that it comprises: The waste heat sensing and acquisition layer is used to monitor the parameters of multiple waste heat sources in the industrial production process in real time. A stepped conversion and refining layer is connected to the waste heat sensing and collection layer, and is used to perform stepped conversion of waste heat according to the waste heat grade. The system according to claim 1, wherein the stepped conversion and refining layer comprises at least: The high-temperature conversion unit is configured to convert primary waste heat into electrical energy using a supercritical carbon dioxide power cycle. The intermediate-temperature conversion unit is configured to convert the waste heat of the second grade into chemical potential energy for storage using a thermochemical adsorption reaction. The low-temperature conversion unit is configured to use a heat pump to raise the temperature of the third-grade waste heat.

[0017] The system according to claim 2 is characterized in that the intermediate temperature conversion unit is a multi-stage cascaded thermochemical energy storage system, which is composed of at least two adsorption energy storage modules connected in series; the first-stage adsorption energy storage module uses a first working fluid pair to process the second-grade waste heat in the higher temperature range; the second-stage adsorption energy storage module uses a second working fluid pair to process the second-grade waste heat in the lower temperature range.

[0018] The system according to claim 3 is characterized in that the first working fluid pair is zeolite-water, the second working fluid pair is silica gel-water; and the refrigerant vapor generated by the second-stage adsorption energy storage module is incorporated into the refrigerant vapor pipeline generated by the first-stage adsorption energy storage module.

[0019] The adsorption energy storage module includes: an adsorption bed, a heat exchanger connected to the adsorption bed, and corresponding valves and pipelines; a shared condenser for condensing refrigerant vapor from each stage of the adsorption energy storage module; and a shared evaporator or storage tank for supplying refrigerant vapor to each stage of the adsorption energy storage module during the exothermic phase. The first-stage adsorption energy storage module is configured to handle heat sources in a first temperature range and uses a first working fluid pair; the second-stage adsorption energy storage module is configured to handle heat sources in a second temperature range below the first temperature range and uses a second working fluid pair. The refrigerant vapor generated by the second-stage adsorption energy storage module is guided to merge with the refrigerant vapor generated by the first-stage adsorption energy storage module before entering the condenser. The point where the medium-pressure vapor generated by the second-stage adsorption energy storage module mixes with the high-pressure vapor generated by the first-stage adsorption energy storage module before entering the condenser is designated as the confluence point.

[0020] A Y-shaped tee pipe is installed at the junction point. The outlets of the adsorption beds of the second-stage adsorption energy storage module and the first-stage adsorption energy storage module are connected to the Y-shaped tee pipe via pipelines, and then connected to the condenser inlet pipe via the Y-shaped tee pipe. This is used to guide the medium-pressure steam generated by the second-stage adsorption energy storage module to merge with the high-pressure steam generated by the first-stage adsorption energy storage module, forming mixed steam, which then flows together to the shared condenser.

[0021] The confluence point is not simply for "combining" the two steam streams, but for achieving a crucial physical process—pressure cascading and energy enhancement. The first stage (zeolite-water) desorbs at 200-300°C, producing high-pressure steam (e.g., pressure P1 = 2 bar). The second stage (silica gel-water) desorbs at 100-200°C, producing medium-pressure steam (e.g., pressure P2 = 1.2 bar). According to fluid mechanics principles, as long as the pressure (P1) in the first-stage adsorption energy storage module's pipeline is higher than the pressure (P2) in the second-stage adsorption energy storage module's pipeline, the medium-pressure steam will be automatically "drawn in" or "pushed" into the high-pressure steam pipeline. A high-precision regulating valve, i.e., a cascaded control high-precision regulating valve, is installed on the pipeline between the outlet of the second-stage adsorption bed and the confluence point. By receiving standardized electrical or pneumatic signals from a controller (such as an MPC), the valve opening can be precisely, continuously, and repeatably adjusted, thereby controlling the fluid flow rate through an automated actuator. Under the command of the MPC controller, the flow rate of medium-pressure steam from the second-stage adsorption energy storage module (second-stage adsorption bed) to the junction point is precisely controlled to maintain the stability of the junction point pressure.

[0022] Control logic (executed by the MPC controller): Real-time monitoring: The sensor continuously measures the actual pressure P1 at the junction point.

[0023] Comparison decision: The controller compares P1 with the set value P_set.

[0024] Execution adjustment: If P1 > P_set, the controller closes the high-precision regulating valve to limit the flow of medium-pressure steam.

[0025] If P1 < P_set, the controller opens the high-precision regulating valve to increase the flow rate of medium-pressure steam.

[0026] Preferably, the first temperature range is 200-300°C; the second temperature range is 100-200°C.

[0027] This invention also provides a control method based on the above system. This method is based on an integrated mathematical model and employs a model predictive control strategy, including the following steps: S1. Real-time acquisition of key system state parameters, including the temperature and pressure of each adsorption bed stage, as well as the pressure at the confluence point; For example, temperature acquisition of each adsorption bed stage: inserting a temperature probe into the interior of the adsorption bed, directly contacting the adsorbent particles or the heat exchanger wall. To obtain more comprehensive temperature field information, an adsorption bed may have multiple temperature sensors installed at different locations (e.g., inlet, outlet, center). Pressure acquisition (P_bed) of each adsorption bed stage: a pressure transmitter is connected to the shell or inlet / outlet pipes of the adsorption bed through a pressure tap (a small nozzle welded to the pipe or container wall) to ensure that the measured pressure is the static pressure of the internal fluid.

[0028] S2. Input the collected parameters into the mathematical model to predict the trend of system state changes within a future time window; S3. Based on the optimization objective, solve for a series of optimal control command sequences within the future time window; S4. Execute the first command in the control command sequence and repeat steps S1-S3 to achieve rolling optimization control.

[0029] The optimization objectives include maintaining pressure stability at the cascade pipeline junction points and maximizing system energy storage efficiency.

[0030] The control commands include at least the command to adjust the opening of the cascaded control valve. For example, at t=0s, the valve opening is precisely adjusted to 32.5%. Then, the system waits for 1 second. At t=1s, the controller remeasures the latest system state (p1, etc.), and then starts from scratch again to predict and optimize for the next 10 seconds, generating a completely new, updated "optimal command sequence," and again only executing the first command of the new sequence.

[0031] This invention further provides a mathematical model supporting the above control method, which integrates the following core equations: 1. Adsorption equilibrium equation: Used to describe the adsorption characteristics of each working fluid pair. in This equation is used to determine the equilibrium adsorption capacity W of the adsorbent at the current temperature T and pressure P.

[0032] For zeolite beds or silica gel beds, the final adsorption capacity W that can be achieved can be calculated under any combination of temperature T and pressure P.

[0033] Adsorption kinetics equation: Used to describe the rate of adsorption / desorption processes, employing a linear driving force model: in The DA equation is used to predict the change in adsorption amount over time. The actual adsorption amount q is controlled by the controller to catch up with the equilibrium adsorption amount q_eq at a corresponding rate; the larger the value of k, the faster the system response.

[0034] Adsorption bed energy balance equation: Used to describe the thermodynamic state of the adsorption bed: This equation is used to calculate the distribution of input heat Q_in among chemical reaction heat, sensible heat, and heat loss, thereby relating the input heat Q_in to the change in bed temperature dT_bed / dt.

[0035] System dynamic response model: Used to describe the dynamic characteristics of the control system loop, employing a first-order time-delay model. This describes the dynamic characteristics of the effect of control commands (such as valve opening changes) on the manifold pressure p1, illustrating how external operations (such as regulating valves) affect the internal state of the system. When the controller issues a command (e.g., adjusting the valve opening from 30% to 35%), it specifies how long (pure time lag τ) and how quickly (time constant T) the manifold pressure P1 responds to this change. K represents the magnitude of the effect.

[0036] The controller evaluates the performance of each control process based on a preset optimization objective function, which is: It is used to correct the deviation between the predicted pressure and the set value, in order to achieve stability.

[0037] Used to correct the severity of valve operation, pursue smoothness, and avoid mechanical wear.

Claims

1. A device for the cascade recovery and utilization of waste heat from isooctane production, characterized in that, include: The waste heat sensing and acquisition layer is used to monitor the parameters of multiple waste heat sources in the isooctane production process in real time. A stepped conversion and refining layer is connected to the waste heat sensing and collection layer, and is used to perform stepped conversion of waste heat according to the waste heat grade. The stepped conversion and refining layer includes at least the following: The high-temperature conversion unit is configured to convert primary waste heat into electrical energy using a supercritical carbon dioxide power cycle. The intermediate-temperature conversion unit is configured to convert the waste heat of the second grade into chemical potential energy for storage using a thermochemical adsorption reaction. The low-temperature conversion unit is configured to use a heat pump to raise the temperature of the third-grade waste heat.

2. The isooctane production waste heat recovery and utilization device according to claim 1, characterized in that, The intermediate-temperature conversion unit is a multi-stage cascaded thermochemical energy storage system, consisting of at least two adsorption energy storage modules connected in series. The first-stage adsorption energy storage module uses a first working fluid pair to process the second-grade waste heat in the higher temperature range. The second-stage adsorption energy storage module uses a second working fluid pair to process the second-grade waste heat in the lower temperature range.

3. The isooctane production waste heat recovery and utilization device according to claim 2, characterized in that, The first working fluid pair is zeolite-water, and the second working fluid pair is silica gel-water; the refrigerant vapor generated by the second-stage adsorption energy storage module is fed into the refrigerant vapor pipeline generated by the first-stage adsorption energy storage module.

4. The isooctane production waste heat recovery and utilization device according to claim 3, characterized in that, The multi-stage cascaded thermochemical energy storage system includes: At least two adsorption energy storage modules connected in series, each stage containing an adsorption bed and a corresponding heat exchanger; A common condenser, the inlet of which is connected to the refrigerant vapor outlet of each stage of the adsorption energy storage module; A common evaporator or liquid storage tank, the outlet of which is connected to the refrigerant inlet of each stage of adsorption energy storage module; The refrigerant vapor generated by the second-stage adsorption energy storage module is guided to merge with the refrigerant vapor generated by the first-stage adsorption energy storage module at the junction point and then enter the condenser together.

5. The isooctane production waste heat recovery and utilization device according to claim 4, characterized in that, A Y-shaped tee pipe is installed at the junction point; the outlet of the second-stage adsorption energy storage module and the outlet of the first-stage adsorption energy storage module are connected to the two inlets of the Y-shaped tee pipe through pipelines, and the outlet of the Y-shaped tee pipe is connected to the pipeline at the inlet of the condenser.

6. The isooctane production waste heat recovery and utilization device according to claim 4 or 5, characterized in that, A cascaded control high-precision regulating valve is installed on the pipeline between the outlet of the second-stage adsorption energy storage module and the junction point to precisely control the flow rate of medium-pressure steam to the junction point in order to maintain the stability of the junction point pressure.

7. A control method for a waste heat recovery and utilization device for isooctane production according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Real-time acquisition of key system status parameters, including the temperature and pressure of each adsorption bed, and the pressure p1 at the confluence point; S2. Input the collected parameters into the mathematical model to predict the trend of system state changes within a future time window; S3. Based on the optimization objective, a series of optimal control command sequences within the future time window are obtained; S4. Execute the first instruction in the control instruction sequence and repeat steps S1-S3.

8. The control method for the isooctane production waste heat cascade recovery and utilization device according to claim 7, characterized in that, The optimization objectives include maintaining the stability of the junction point pressure p1 and maximizing the system energy storage efficiency; the control commands include at least the adjustment command for the opening of the cascaded high-precision regulating valve.

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