1. Field of the Invention
The invention relates an ignition system for a biomass-fueled furnace, and more particularly toward an electronically controlled igniter for a biomass furnace capable of automatically reigniting fuel in a combustion chamber on a sensed demand basis.
2. Related Art
Biomass refers to living and recently dead biological material that can be used as fuel. Most commonly, biomass includes plant matter grown for use as biofuel, as well as biodegradable wastes that can be burned as fuel. Production of biomass is a growing industry as interest in sustainable fuel sources grows.
A biomass furnace is an appliance that burns biomass materials, usually in pelletized form, to create a source of distributable energy for residential, commercial and/or industrial spaces. Water and/or air is often used as an intermediate thermal fluid which is brought near to the hot combustion gases, absorbing heat energy and distributing that heat energy to a remote space to be heated through pipes, ducts or the like. By way of definition, the term “furnace” is used here in its broadest sense to mean any boiler, forced air, free-standing stove or other type of heating unit.
By slowly feeding fuel into a combustion chamber area, sometimes referred to as a burn pot, biomass furnaces can maintain continuous combustion that require little to no physical adjustments, thus creating a reliable, even and continuous source of heat energy. Biomass furnaces have become a viable, economical and popular option for heating systems.
Many of the commercially available solid biomass combustion devices, including hot water boilers, furnaces, pellet stoves and the like, rely on a high degree of user intervention to maintain consistent operation. In the case of corn stoves for example, residual klinkers must be removed from the burn pot on a regular basis. Likewise, other ash and residues must be frequently cleaned. The automation level in such stoves is very low and does not support unattended operation for extended periods. In addition, ignition of the fuel in a biomass furnace is a somewhat complicated matter. The user is typically required to manually initiate the combustion process using an extraneous ignition source, flammable liquids, gels or tinder. Ignition of the biomass fuel is so inconvenient that biomass furnaces are usually set to operate constantly at a minimum level even when there is little or no demand for heat. This continuous operation of the furnace is meant to ensure that the fire does have to be relit. Thus, at times of low demand, prior art biomass furnaces would rather waste fuel needlessly rather than inconvenience the operator to restart the combustion process.
Accordingly, there is a need for a simple ignition system for biomass furnaces which does not require any user intervention, and that can rival the customary automation levels associated with oil and gas-fired furnaces and boilers.
According to a first aspect of this invention, an automatic ignition system is provided for a biomass-fueled furnace. The ignition system comprises a plenum and a fan operatively associated with the plenum. The fan forcibly moves air through the plenum toward a biomass fuel combustion chamber. An auxiliary heat source is configured to heat the air moved through the plenum to an elevated auto-ignition temperature. At least one temperature sensor is provided, along with a control module. The control module is configured to automatically activate the auxiliary heat source in response to the temperature at the temperature sensor falling below a preset limit. According to this aspect of the invention, the automatic ignition system functions to initiate the combustion process by superheating air delivered to the combustion chamber so that biomass fuel in the combustion chamber spontaneously ignites.
According to another aspect of this invention, a biomass furnace is provided of the type for heating an intermediate thermal fluid in response to the combustion of a biomass fuel. The furnace comprises a combustion chamber that is configured to receive biomass fuel in incremental quantities and to combust the biomass fuel therein to produce hot combustion gases. An exhaust flue is provided for conducting the hot combustion gases away from the combustion chamber. A heat exchanger, proximate the combustion chamber and/or the flue, channels a thermal fluid (e.g., air or water) to absorb heat energy from the combustion gases. A plenum leads to the combustion chamber. A fan, operatively associated with the plenum, forcibly moves air through the plenum toward the biomass fuel contained in the combustion chamber. An auxiliary heat source heats the air moved through the plenum to an elevated auto-ignition temperature. At least one temperature sensor is provided along with the control module. The control module automatically activates the auxiliary heat source in response to the temperature at the temperature sensor falling below a preset limit. Accordingly, the biomass furnace is useful in both hot water and forced air type heating systems, and enables optimal cycling on and off of the combustion process on a demand basis. When the temperature at some sensed location falls below a preset limit, the control module automatically activates the auxiliary heat source, which pumps superheated air into the biomass fuel in the combustion chamber, thereby auto-igniting the biomass fuel and restarting the combustion process.
According to yet another aspect of this invention, a method is provided for igniting a solid biomass fuel in a furnace of the type for heating an intermediate thermal fluid in response to an external signal or command. The method comprises the steps of: providing a combustion chamber, holding a quantity of solid biomass fuel in the combustion chamber in the absence of flame, the biomass fuel having a characteristic auto-ignition temperature, superheating air to a temperature above the auto-ignition temperature of the biomass fuel in the combustion chamber, and injecting the heated air into the combustion chamber so that at least a portion of the solid biomass fuel in the combustion chamber spontaneously combusts.
According to yet another aspect of this invention, a method is provided for controlling the ignition of a solid biomass fuel in a biomass furnace. The method comprises the steps of providing a furnace having a combustion chamber configured to receive biomass fuel in incremental quantities, where the solid biomass fuel has a characteristic auto-ignition temperature. A quantity of the solid biomass fuel in the combustion chamber is combusted to produce hot combustion gases. A thermal fluid is channeled through the hot combustion gases to absorb heat energy therefrom and transport the heat energy to a remote space to be heated. The temperature of the thermal fluid or the space to be heated is monitored to determine a control temperature. When the control temperature reaches a predefined upper limit, the combustion step is terminated thus stopping the generation of new heat energy. When the control temperature reaches a defined lower limit, the combusting step is automatically resumed. This step of automatically resuming combustion includes raising the temperature of the solid biomass fuel above its auto-ignition temperature in the absence of flame.
Accordingly, the subject invention overcomes the shortcomings and disadvantages characteristic of prior art designs by providing a simple ignition system which does not require user intervention and that can rival the customary automation levels associated with prior art oil and gas-fired furnaces and boilers.
These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein:
Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views,
Combustion of the fuel 16 in the combustion chamber 14 produces hot combustion gases. These hot combustion gases interact with an intermediate thermal fluid through some type of heat exchanger 21. In the case of a boiler arrangement like that shown in
Turning now to
In the preferred embodiment of this invention, the auto-ignition system 28 takes advantage of the fact that nearly all solid biomass materials have an auto-ignition temperature which is defined as the lowest temperature at which the biomass material will spontaneously ignite in a normal atmosphere without an external source of ignition. In other words, without a flame or spark, a biomass material will spontaneously combust in a normal atmosphere at its auto-ignition temperature. Common solid biomass auto-ignition temperatures are in the range of 350-800° Fahrenheit.
The auto-ignition system 28 includes a plenum 30 leading to the combustion chamber 14. The plenum 30 is here shown as a tubular duct, but could be rectangular in cross-section or otherwise shaped. A fan 32 is motor driven to pump air. The fan 32 is operatively associated with the plenum 30 so as to forcibly move air through the plenum 30 toward the biomass fuel 16 contained in the combustion chamber 14. The plenum 30 and fan 32 may be either an integral part of the biomass furnace combustion process, continuously delivering combustion air to the combustion chamber 14 during normal operation of the stove, or may be a separate device altogether which is activated only during ignition and then switched off. In this latter case, the plenum 30 could be wholly separate and distinct from the delivery of combustion air to the chamber 14, or may be shared between the combustion air delivery system and the auto-ignition system 28. In other words, the auto-ignition system 28 can be either a wholly distinct unit from the normal combustion air pump system of a biomass furnace, or can be shared with the combustion air system, or can be fully integrated into the combustion air system.
An auxiliary heat source 34 heats the air moved through the plenum 30 to an elevated auto-ignition temperature. In other words, the auxiliary heat source 34 is capable of raising the temperature of air moved through the plenum 30 above the auto-ignition temperature of the biomass fuel 16 contained in the combustion chamber 14. In one exemplary embodiment of this invention, the auxiliary heat source 34 is contained within the plenum 30 in an in-line fashion like that shown in
A control module 36 is operatively connected to the fan 32 and the auxiliary heat source 34, such as via electrical wires. The control module 36 is preferably a microprocessor based system, but may be of any type which is effective to control operation of the auxiliary heat source 34, and preferably also the fan 32, in response to sensed conditions. Along these lines, the auto-ignition system 28 includes at least one, but preferably two, temperature sensors—a thermal fluid sensor 38 and a combustion temperature sensor 40. The thermal fluid sensor 38 is positioned either in the stream of thermal fluid (
It is only necessary to operate the auxiliary heat source 34 of the auto-ignition system 38 so long as fuel 16 in the combustion chamber 14 is not capable of sustained combustion. Once a sufficient flame has been established in the combustion chamber 14, the auxiliary heat source 34 can be deactivated. If the fan 32 is not required for providing combustion air, the fan 32 can also be stopped at this time. For these purposes, the combustion temperature sensor 40 is provided near the combustion chamber 14 or perhaps in the flue 26 or other suitable location, to monitor combustion gas temperatures. When the combustion gas temperatures at the point of the combustion temperature sensor 40 reach a preset limit, the control module 36 will deactivate the auxiliary heat source 34, and possibly also the fan 32, thereby discontinuing the auto-ignition operation. In this manner, the auto-ignition system 28 operates on a demand basis, pumping superheated air into the combustion chamber 14 only when it is necessary to restart the combustion process.
Temperature measurements from the combustion temperature sensor 40 are depicted by line 140 in
The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and fall within the scope of the invention. Accordingly the scope of legal protection afforded this invention can only be determined by studying the following claims.
This application claims priority to U.S. Provisional Patent Application No. 61/047,791, filed on Apr. 25, 2008 which is incorporated by reference herein in its entirety.
Number | Date | Country | |
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61047791 | Apr 2008 | US |