Self-regulating negative pressure maintenance system for industrial combustion processes

Abstract

A system comprises an exhaust gas ejector 1 and an induced draft fan 2 installed within an exhaust gas duct of an industrial combustion process 3. A system integrated into the combustion process redirects high-pressure motive steam to the ejector on detection of a failure of the induced draft fan, creating a suction effect which draws exhaust gases through a venturi passage of the ejector to maintain a negative pressure during a shutdown of the process. The exhaust gas ejector may be in series with the induced draft fan, or they may be in parallel with a changeover damper system 6 switching a flow path between the exhaust gas ejector and the induced draft fan. The combustion process may comprise pyrolysis, gasification, or a solid fuel combustion process. Corresponding methods are also claimed.

Description

The present invention provides a comprehensive system and method for maintaining negative pressure within an industrial combustion Process during all potential Induced Draft (ID) Fan failure scenarios, including failures of the fan motor or inverter. The invention comprises an Exhaust Gas Ejector utilizing high-pressure motive steam installed in the Exhaust Gas Ductwork. Upon ID Fan failure, Valves send steam to the Ejector, creating suction that draws Exhaust Gases through the Ductwork and maintains negative pressure during Process shutdown. While certain pyrolysis and gasification systems may utilize pressure control mechanisms, the present invention specifically addresses the problem of induced draft fan failure through the integration of a steam ejector system to maintain negative pressure during shutdown, which is not addressed by existing pressure control techniques. Several innovative configurations of the Exhaust Gas Ejector integrated with the ID Fan are possible, including in-series, parallel with Bypass Dampers, and parallel with Changeover Dampers. The steam-powered Ejector provides a simple, reliable solution with few moving parts to address all ID Fan failure scenarios. It enables quick response to prevent pressure loss, integrates advantageously with existing Steam Generation Systems, and allows the declining Steam Supply to self-regulate with decreasing Exhaust Gas Flow. Processes utilizing Pyrolysis, Gasification or with remaining combustible material can fully treat Exhaust Gases during emergency shutdowns. The robust, comprehensive Ejector System maintains negative pressure, reduces environmental risks, and enables safe industrial combustion Process shutdowns. Definitions: Changeover Dampers - Dampers or valves used to switch flow paths between the ID Fan and Exhaust Gas Ejector to prevent recirculation. Dump Stack - A stack or vent used to discharge unburnt gases directly to the atmosphere near their generation point. Electrical Grid - The interconnected network for distributing electrical power generated at centralized locations. Exhaust Gas Ejector - A device using high-pressure motive steam to create suction and draw gases through a venturi-shaped passage. Exhaust Stack - A vertical duct or chimney used to discharge exhaust gases from a process into the atmosphere. Flue Gas Treatment Equipment - Systems used to remove pollutants and contaminants from exhaust gases before discharge to the atmosphere. Heat Recovery Boiler - A type of boiler that recovers heat from hot exhaust gases to generate steam. Induced Draft (ID) Fan - A fan used to induce or draw exhaust gases through a process or ductwork by creating negative pressure. In industrial combustion processes, the ID fan is typically the primary system component responsible for maintaining negative pressure within the process ductwork. Inlet Vane Dampers - Adjustable vanes at the inlet of a fan used to control and restrict airflow. Islanding Mode - An operating mode where a local power generation system runs independently from the electrical grid. Motive Steam - The high-pressure steam supplied to an Exhaust Gas Ejector to create the suction effect. Pyrolysis - A thermochemical process decomposing materials at elevated temperatures in an inert atmosphere. In the context of industrial combustion processes, pyrolysis technologies may be employed for waste treatment or gasification processes, generating combustible gases that require safe handling and combustion. Sensible Heat - Thermal energy contained within a substance that contributes to its temperature. Steam Generation Set - An assembly including a heat recovery boiler and steam turbine generator system. Uninterruptible Power Supply (UPS) - A backup power source providing emergency battery power during electrical grid outages. List of Figures The invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows a schematic representation of an Exhaust Gas Ejector in series with an ID Fan. Figure 2 shows a schematic representation of an Exhaust Gas Ejector in series with an ID Fan and in parallel with a Bypass. Figure 3 shows a schematic representation of an Exhaust Gas Ejector in parallel with an ID Fan. Figure 4 shows a schematic representation of an Exhaust Gas Ejector pressure control system. Existing Techniques For Managing ID Fan Failure There are several conventional techniques to manage Induced Draft (ID) Fan failure for combustion Processes: A. Managing Fuel Supply and Dump Stacks: • Stopping fuel supply: For Processes combusting fossil fuels, the fuel supply can be stopped immediately upon detecting a loss of electrical supply or an ID Fan failure. However, this technique is ineffective for Processes combusting solid fuels, or those utilizing Pyrolysis and Gasification Technologies, where substantial quantities of fuel and sensible heat remain within the Process, continuing to generate combustible gases. In these cases, Process pressure must be maintained during shutdown. • Dump Stacks: Dump Stacks enable non-combusted gases to be vented to the atmosphere near their generation point, preventing the buildup of pressure and unburnt gases within the Process. However, this technique is less common now due to environmental concerns over uncontrolled emissions. B. Managing Loss of Electrical Power Supply: • Standby Generators: Standby Generators can be provided. Upon power loss, the Generator starts up, and power is restored to the ID Fan within a few seconds. However, the Standby Generator must be highly reliable, incurring significant capital and operating costs. • Uninterruptible Power Supply (UPS): A large UPS with a battery bank can maintain power to the ID Fan upon electrical power loss. However, the battery bank must have a large capacity to sustain ID Fan operation for an extended duration, resulting in considerable capital costs. • Steam Generation Set: Some combustion Processes utilize Heat Recovery Boilers and Steam Generation Sets for energy recovery. The control equipment for these Sets can be upgraded to enable "islanding mode" operation, where the Steam Generation Set runs independent of the electrical grid and supplies power to the ID Fan upon power loss. While the Steam Flow Rate and electrical power generation will decline as the Process shuts down, problems can occur when the Steam Flow Rate drops below the minimum acceptable to the Steam Turbine. C. Managing Failure of Inverter or Fan Motor: • Steam-driven ID Fans: Steam Drives are sometimes used in critical petrochemical applications. However, this solution has high capital and operating costs and is often not feasible for combustion Processes. • Duty and Standby ID Fans: Alternatively, Duty and Standby ID Fans with Changeover Dampers can be used to manage Inverter or Motor failures, but at a high capital cost. The techniques mentioned above do not address all potential failure scenarios. The present invention provides a solution to maintain negative pressure within the Process comprehensively, including any ID Fan failure, Motor failure, or Inverter failure. While the above techniques address individual scenarios, none offer a comprehensive solution to maintain negative pressure during all potential ID Fan failure situations, including motor and inverter failures. Furthermore, these techniques often involve significant capital and operating costs, reliability concerns, or environmental drawbacks. The present invention overcomes these limitations by providing a simple, reliable, and cost-effective solution that can be easily integrated into existing industrial combustion processes. Discussion of Prior Art Conventional industrial combustion Processes often rely on a single, electrically powered Induced Draft (ID) Fan to draw Exhaust Gases through the Process ducting and maintain negative pressure within the system. However, this approach is vulnerable to failures or disruptions that can cause a loss of negative pressure and potentially lead to uncontrolled releases of Exhaust Gases. The field of industrial combustion processes has a rich history of utilizing various techniques and technologies to manage induced draft (ID) fan failures and maintain negative pressure within process ductwork. One notable area of prior art in this field includes the use of steam-powered ejectors, as exemplified by devices such as the Lempor Ejector historically employed in steam engines. Steam ejectors have been utilized extensively in steam engines to induce draft through fireboxes and exhaust systems by leveraging high-pressure motive steam to create a suction effect, drawing gases through a venturi-shaped passage. These devices have played a crucial role in facilitating efficient combustion and exhaust management in steam-powered systems. While steam ejectors have been widely employed in steam engines, the specific adaptation of this technology for maintaining negative pressure within industrial combustion processes during ID fan failure scenarios presents novel challenges and opportunities for innovation. Existing techniques relying solely on electrically powered ID fans are prone to failure, risking uncontrolled releases of exhaust gases, safety hazards, and environmental contamination. The present invention overcomes these limitations by providing a comprehensive solution that can be easily integrated into existing industrial combustion processes, addressing all potential ID fan failure scenarios, including motor and inverter failures. Furthermore, the invention introduces a self-regulating mechanism to adjust steam flow rates in response to changing exhaust gas flows during shutdown, ensuring continuous operation without external intervention. The utilization of steam ejectors in steam engines represents a well-established practice for creating suction or vacuum conditions, demonstrating the effectiveness of this technology in industrial settings. Steam ejectors are also widely employed in chemical and petrochemical industries for applications requiring negative pressure or vacuum. However, while the basic principle of steam ejectors is known, the specific implementation and integration of a steam ejector system to maintain negative pressure upon induced draft (ID) fan failure in an industrial combustion process presents novel challenges and opportunities for innovation. The application and configuration of a steam ejector system specifically for addressing ID fan failure scenarios, as claimed in the present invention, differentiates it from existing steam ejector implementations in other industries. In the context of the present invention, it is important to acknowledge the existence of prior art related to steam ejectors and their historical applications in steam engines. By recognizing and referencing this prior art, we aim to provide a comprehensive understanding of the technological landscape and highlight the specific advancements and innovations introduced by the current invention. Furthermore, the discussion of prior art allows us to distinguish the claimed invention from existing technologies, emphasizing any novel features, improvements, or specific applications that differentiate it from prior art. This comparative analysis underscores the novelty and inventive step of the current invention and strengthens the patent application by providing context for the claimed invention and supporting arguments for its patentability. Detailed Description of the Invention The invention comprises an Exhaust Gas Ejector installed within Exhaust Gas Ductwork to maintain the Process within normal operating pressure in the event of failure of the ID Fan. An Exhaust Gas Ejector uses a high-pressure steam to create a suction effect within a Venturi shaped device. The Exhaust Gas Ejector is a simple device with few moving parts, providing a reliable and cost-effective solution for maintaining negative pressure. Many combustion Processes already include steam generation for heat recovery, making the integration of the steam-powered Exhaust Gas Ejector particularly advantageous. If the ID Fan fails and can no longer maintain the Process pressure, motive steam is sent to the Exhaust Gas Ejector, which develops a pressure drop across itself and maintains the Process operating pressure while the Process is safely shut down. The Exhaust Gas Ejector allows any fuel gases generated by Pyrolysis and Gasification Technologies during an emergency shutdown to be fully combusted and treated in the flue gas treatment equipment, reducing environmental risks. A key advantage of the invention is the inherent synergy between the declining steam supply from the heat recovery system and the declining exhaust gas flow as the Process shuts down. As combustion diminishes and exhaust gases decrease, the heat recovery steam generation also declines at an approximately matched rate. This allows the motive steam demand for the Exhaust Gas Ejector to selfregulate, ensuring sufficient steam supply is available throughout the shutdown sequence. While control systems regulate the motive steam flow, the integrated design takes advantage of the natural decline in steam production to match the decreasing exhaust gas flow requirements. This self-regulating behaviour, where the declining steam supply matches the decreasing exhaust gas flow during shutdown, is a novel feature of the present invention, not found in existing techniques for maintaining negative pressure. Several configurations can be used as shown in Figures 1, 2 &3. In Figure 1, the Exhaust Gas Ejector (1) is installed in series with the ID Fan (2). During normal operation, the ID Fan is used to draw gases through the Process (3), then discharge them through the Exhaust Gas Ejector and the Exhaust Stack (4), where the Exhaust Gases are discharged into the atmosphere. The ID Fan maintains the Process at the correct operating pressure. If the ID Fan fails and can no longer maintain the Process pressure, motive steam is sent to the Exhaust Gas Ejector, which develops a pressure drop across itself and maintains the Process operating pressure while the Process is safely shut down. In Figure 2, the Exhaust Gas Ejector (1) is installed in parallel with a Bypass Damper (5) and in series with the ID Fan (2). During normal operation, the ID Fan draws gases through the Process (3) and discharges them through the Bypass Damper and onto the Exhaust Stack (4), where the Exhaust Gases are discharged into the atmosphere. The ID Fan maintains the Process at the correct operating pressure. If the ID Fan fails and can no longer maintain the Process pressure, the Bypass Damper is closed, and motive steam is sent to the Exhaust Gas Ejector. The Exhaust Gas Ejector then develops a pressure drop across itself and maintains the Process operating pressure while the Process is safely shut down. The Bypass Damper prevents the recirculation of Exhaust Gases when the Exhaust Gas Ejector is operating. The Bypass Damper can be any type of valve, including a non-return valve, and can be specified by anyone skilled in the art. In Figure 3, the Exhaust Gas Ejector (1) is installed in parallel with the ID Fan (2). During normal operation, the ID Fan draws gases through the Process (3) and discharges them through the Exhaust Stack (4), where the Exhaust Gases are discharged into the atmosphere. The ID Fan maintains the Process at the correct operating pressure. If the ID Fan fails and can no longer maintain the Process pressure, the Changeover Damper System (6) changes position, and motive steam is sent to the Exhaust Gas Ejector. The Exhaust Gas Ejector then develops a pressure drop across itself and maintains the Process operating pressure while the Process is safely shut down. The Changeover Damper System prevents the recirculation of Exhaust Gases when either the ID Fan or the Exhaust Gas Ejector is operating. The Changeover Damper System can comprise various configurations associated with the location and type of valves, such as non-return valves or three-way valves. The optimal configuration can be specified by someone skilled in the art. During normal operation using the ID Fan (2), the pressure within the Process is controlled using conventional monitoring and control techniques. Typically, a Pressure Transmitter (7) and Flow Transmitter (8), combined with a controller, are used to adjust the speed of the ID Fan and / or the position of inlet vane dampers. When the ID Fan has failed, the Exhaust Gas Ejector (1) maintains the operating pressure within the Process by adjusting the motive steam pressure or flow rate. Figure 4 shows how the motive steam pressure is controlled using a Modulating Valve (8) and activated using a Quick-Opening Valve (9). Another option is to use a single quick-opening modulating valve. The Modulating Valve is often a globe-type valve, but a needle-type flow control valve can also be used. Several important features of the motive steam and Damper control systems are: 1. The motive steam control system must provide a quick transition from ID Fan operation to Exhaust Gas Ejector operation. 2. The motive steam control system must provide a smooth transition from ID Fan operation to Exhaust Gas Ejector operation. 3. The motive steam control system must provide reliable and safe operation since it may be considered a safety-critical system. 4. The motive steam control system must ensure that the upstream Process is protected from excessive suction that may occur under low-flow conditions and high motive steam flow. Using conventional control system techniques, someone skilled in the art can specify a motive steam control system that accommodates the features listed above.

Claims

1. A system for maintaining negative pressure within an industrial combustion process, comprising:• an Exhaust Gas Ductwork;• an Exhaust Gas Ejector and an Induced Draft (ID) Fan both installed within the Exhaust Gas Ductwork, wherein the Exhaust Gas Ejector uses high-pressure motive steam to create a suction effect and draw exhaust gases through a Venturi-shaped passage;• and a system integrated into an industrial combustion process configured to redirect the high-pressure motive steam to the Exhaust Gas Ejector upon failure of the Induced Draft (ID) Fan, thereby maintaining negative pressure within the process during shutdown.

2. A method for maintaining negative pressure within an industrial combustion process during induced draft (ID) fan failure scenarios, comprising the steps of:• providing an exhaust gas ejector within Exhaust Gas Ductwork of the combustion process;• supplying high-pressure motive steam to the Exhaust Gas Ejector;• detecting failure of the ID fan to maintain Process pressure;• directing the motive steam to the Exhaust Gas Ejector upon ID Fan failure to create a suction effect, thereby maintaining negative pressure within the combustion process.

3. A method for maintaining negative pressure within an industrial combustion process, wherein the industrial combustion process comprises at least one of Pyrolysis, Gasification, or combustion of solid fuels with remaining sensible heat, the method comprising:• detecting a failure of an Induced Draft (ID) Fan;• directing high-pressure motive steam to an Exhaust Gas Ejector installed within Exhaust Gas Ductwork, wherein the Exhaust Gas Ejector uses the motive steam to create a suction effect and draw exhaust gases through a Venturi-shaped passage;• and adjusting the motive steam pressure or flow rate to maintain negative pressure within the process as the exhaust gas flow decreases during shutdown.

4. The system of claim 1, wherein the exhaust gas ejector is configured in series with the ID fan within the exhaust gas ductwork.

5. The system of claim 1, wherein the Exhaust Gas Ejector is installed in parallel with the ID Fan and a Changeover Damper System, wherein the Changeover Damper System switches flow paths between the ID Fan and the Exhaust Gas Ejector to prevent recirculation of exhaust gases.

6. The system of claim 1, wherein the exhaust gas ejector is configured in parallel with the ID fan within the exhaust gas ductwork, and further comprising a changeover damper system to prevent recirculation of exhaust gases.

7. The method of claim 2, further comprising regulating the motive steam flow rate to ensure smooth transition from ID fan operation to exhaust gas ejector operation upon detection of ID fan failure.

8. The method of claim 2, further comprising ensuring the motive steam control system's reliable and safe operation to prevent excessive suction under low-flow conditions and high motive steam flow.

9. The system of claim 1, wherein the combustion process utilizes pyrolysis, gasification, or solid fuel combustion technologies.

10. The system of claim 1, wherein the exhaust gas ejector enables full treatment of fuel gases generated during emergency shutdowns in the combustion process.

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