US20080102411A1

US20080102411A1 - Apparatus and methods for conditioning combustion air

Info

Publication number: US20080102411A1
Application number: US11/927,088
Authority: US
Inventors: Robert Longardner
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-10-30
Filing date: 2007-10-29
Publication date: 2008-05-01

Abstract

Devices and methods for adjusting the physical properties of air used in the combustion of carbon based fuels are described. Parameters such as air temperature, pressure and moisture content are adjusted before the air is delivered to a combustion chamber of devices such as furnaces, boiler and the like. The physical properties of the air may be are adjusted such that a predetermined amount of oxygen and/or water are delivered to the combustion chamber. In one embodiment the amount of oxygen and/or moisture delivered by the intake air is optimized to increase the efficiency of the carbon fuel burned in combustion and/or to minimize the production of compounds such as NO_XSO₂, CO, CO₂and the like.

Description

PRIORITY CLAIM

This application claims the benefit of U.S. Provisional Patent Application No. 60/855,333, filed on Oct. 30, 2006, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

Aspects of the disclosure relate generally to combustion, devices and methods to achieve more efficient and/or more environmentally sound combustion of carbon based fuels.

BACKGROUND

The present invention relates to methods of reducing the formation of NOx, SO₂, ash and particulate during carbon combustion. The stoichiometry of the combustion of hydrocarbon fuels is, as follows: to completely bum, about 1 pound (#) of carbon requires about 2.67# of oxygen or 11.52#s of air as measured under standard conditions. Complete combustion of 1 # of a hydrocarbon fuel produces about 14,200 BTUs of heat. For complete combustion additional oxygen is required if the combustion chamber includes combustionable materials besides hydrocarbon. For example, hydrogen in present in either the intake air or fuel reacts with oxygen during combustion to form water or vapor.
On a volumetric basis, about 150 cubic feet (cuft) of intake air at 50° F. and 100% Rh weighs about 11.52#s, while the same weight of air occupies about 180 cuft when the intake air is 110° F. and 40% Rh. Varying ambient conditions, such as barometric pressures, ambient temperature and specific moisture, make it difficult to meter precisely the amount of intake air comprising the amount of oxygen required for optimal or at least consistent combustion. When intake air exceeds the gravimetric, stoichiometric need for oxygen, the amount of secondary products formed by combustion such as CO, NOx, SO₂, ash, particulate and heat changes; in general combustion efficiency decreases as the amount of heat generated increases.
When the ambient profile of intake air flow is metered based upon the. downstream sensing of the products of combustion: the amount of oxygen present during combustion usually exceeds the stoichiometric amount required for optimal combustion. This can result in the formation of excessive amounts of secondary combustion products, all of which must be heated to stack effluent temperature thereby increasing the heat rate. This increase is normally to a stoichiometric ratio that is sub-optimal, it is possible to control the vapor pressure level by controlling the temperature of the intake air, thereby helping to optimize the amount of oxygen present at combustion.

SUMMARY

One embodiment is a method for treating intake air used in the combustion of carbon based fuels so as to minimize the level of at least one undesirable product of combustion, such as NOx, SO₂, CO, excess heat, excess CO₂, and the like.
One embodiment includes devices and methods for optimizing combustion by conditioning intake air so as to regulate the gravimetric amount of oxygen in the intake air regardless of the intake air source's ambient temperature and specific humidity.
Still another embodiment is a device for conditioning air in carbon based fuel burning system comprising: an intake air chamber for conditioning ambient air; a combustion chamber, and at least one sensor for measuring physical parameters of air in said air intake chamber, wherein the intake air chamber can be adjusted so as to control the temperature and moisture content of ambient air drawn into said chamber, and wherein said chamber is positioned so as to feed air into the combustion chamber.
In one embodiment the intake air conditioning device includes a heat transfer coil. In yet another embodiment the intake air conditioning device includes equipment for adjusting the amount of water, or water vapor to air in the intake air. Before air is delivered to the combustion chamber it is conditioned such that the air introduced into the combustion chamber if includes an amount of oxygen and/or water sufficient for the efficient combustion of the amount of carbon based fuel burned in the combustion chamber. In one embodiment the intake air is conditioned so as to minimize the production of wasteful and/or environmentally unwanted compounds such as soot, NOx, SOx CO, excess CO₂and the like.
One embodiment is a method for regulating the efficient combustion of carbon based fuels, comprising the steps of providing an intake air conditioner device, and supplying at least one sensor that measures the physical characteristic of ambient air, such as temperature, humidity and the like; and a computer that calculates the amount of heat that needs to be added or removed from the air so as to deliver a volume of air that includes a weight of oxygen necessary for burning given amount of a carbon based fuel.
One embodiment includes equipment for adjusting the temperature, pressure and and/or moisture content of the intake air so as to promote clean and efficient combustion of carbon based fuel conditions within the intake air conditioning chamber so as to optimize combustion. In one embodiment the intake air conditioner device is located between a source of ambient air and a combustion chamber. In another embodiment the computer having calculated the optimum volume of air necessary to deliver a given mass of oxygen to the combustion chamber signals components of the intake air conditioner device to adjust the temperature, pressure and/or Rh of the intake air before introducing the air into the combustion chamber, to ensure clean and efficient combustion of the carbon based fuel.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. Fraction of Oxygen in Air at a Ratio of 23% of Dry Air.
FIG. 2. Psychrometrics of Primary and Secondary Combustion Air.
FIG. 3. Comparison of superheated vapor removal calculated for ambient air at about 60% to about 100% Rh. These values were calculated for the removal of moisture in terms of amount removed/Hr., or moisture Residual/Hr. for a hypothetical power generation unit producing on the order of about 300 m W/Unit.
FIG. 4. Psychrometric calculation for ambient intake air. Combined intake air of combustion air calculated for a hypothetical power generation unit that produces on the order of about 300 mW/Unit.
FIG. 5. A plot of pre-heater temperatures of ambient air used as the source of either primary and/or secondary combustion air.
FIG. 6. A table of example calculations illustrating the effect on combustion efficiency of different ratios of intake air to fuel. The table includes data illustrating the amount of refrigeration calculated in tons/Hr. required to condition ambient air as shown in the table for a hypothetical power generation unit producing on the order of about 300 mW/Unit.
FIG. 7. A diagram showing some parts of a typical air handling system constructed in accordance with some embodiments disclosed herein used to burn carbon based fuels.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principle of the invention, reference will now be made to the embodiment illustrated in the drawing and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.
The term ‘about’ refers to on the order of 15 percent more or 15-percent less than the value of given number. For example, about 10 is between 8.5 and 11.5.
The term ‘optimal’ refers to an improved set of conditions and not necessarily to the hypothetical maximum or best imagined value for a given set of conditions.
The gravimetrics of combustion intake air varies with ambient conditions the fraction of air that is oxygen under standard temperature and pressure is about 21% by volume or 23% by weight. Referring now to FIG. 1, the amount of oxygen per cuft at 200° F. is about 1/12^ththe amount of oxygen available per cuft of air at 0° F. The oxygen for complete combustion gravimetrically is generally controlled volumetrically. In most systems the physics of combustion is based upon monitoring the products of combustion and the ignition temperature. One aspect disclosed herein, is a method for conditioning combustion intake air to a constant temperature, (or range of temperatures) and a specific humidity (or range of specific humidity values). The temperature and or moisture content of the air is optimized such that the intake air delivered to the combustion chamber has an optimal or near optimal tachometric amount of oxygen and/or water necessary for clean and efficient combustion.
The fraction of dry gas in the intake air decreases as the temperature of the ambient air increases. This corresponds with the wetting effect, ‘waste heat’ is required to burn the carbon in the fuel combusted with non-conditioned intake air and combustion under these conditions requires about 10 to about 25% more fuel. The result is the added expense of burning additional fuel and the production of additional CO₂a greenhouse gas.
Under ignition and combustion conditions water vapor is neither combustible nor does it support combustion. Accordingly, to the extent that water vapor in the combustion chamber displaces oxygen rich air or combustible fuel it reduces the efficiency of combustion. One embodiment disclosed herein operates to reduce the amount of water and/or water vapor in the combustion chamber by means of drying at least one the following: the primary intake air, then secondary intake air or the soot blowing air.
The superheated vapor in ambient intake air can wet the chemistry of combustion. Unstable ignition temperatures may result, because of varying specific moisture levels in ambient air caused by a reduction in the ‘sensed’ air temperature this may increase the heat rate. A further complication results when the volume or amount of the intake air is controlled by an analysis of the products of combustion downstream from the ignition zone. In one embodiment described herein, the amount of intake air is regulated and controlled upstream from the ignition zone, thereby better optimizing the stoichiometry of fuel combustion.
The chemistry of combustion, including the ignition temperature, is influenced by the amount of water in the combustion chamber at the time of ignition. One embodiment serves to stabilize ignition and combustion by conditioning the intake air to a constant range of Rh values. In one embodiment the intake air is conditioned to a constant temperature and specific moisture (saturation at a given temperature) of about 50° F. and about 100% Rh.
Referring now to FIG. 2, the wetting effect of superheat vapor (condensate) according to one aspect. In this example, the wetting effect is calculated for a hypothetical coal steam unit producing 300 mW coal steam plant reduces the fuel consumption as depicted in FIG. 2. In a typical coal fueled power plant air referred to as primary air issued to at least aid in the delivery of pulverized coal into the combustion chamber. (See, for example, FIG. 7). Typically the primary air is on the order of about 20 percent of the air introduced into the combustion chamber. Referring again to FIG. 2, there is usually at least some water adhering to the surface of coal used to generate power. According to one embodiment disclosed herein, the ambient air used a source of primary air is dried such that the primary a helps to remove moisture from the surface of the coal immediately prior to the coal's introduction into the combustion chamber. The values presented in FIG. 2 illustrate the effect on combustion efficiency of using dried ambient air in the primary and secondary intake air streams. In this example, primary intake air makes-up on the order of about 20% of the total air introduced into combustion and secondary air makes-up on the order of about 80% of the total air of combustion. The primary air is re-wetted as it strips surface moisture from the pulverized coal being fed into the combustion chamber.
The combustion of fuel is generally analyzed on a weight (or mass) basis, but oxygen laden combustion air is generally supplied to combustion chambers on a volumetric basis. The amount of oxygen necessary for the stoichiometric burning of fuel is a percentage of the volume of air; the weight of a unit volume of air is based upon factors including the ambient temperature, pressure, and specific moisture (relative humidity) of the air. The factors that determine the volume air relative to its weight can change at almost any time. Accordingly, for optimal combustion it is necessary to constantly measure these conditions and to condition the intake air accordingly. Embodiments disclosed herein provide general and specific devices and methods to condition the intake air to the furnace (both primary and secondary air) in order to better optimize combustion. Intake air can be conditioned to remove excess specific moisture or to condition the air range that is in conformity with the air handling capacity of a given system. For example, intake air can be conditioned to about 50° F. and about 100% Rh, or almost any other range of values that is best suited for the burning of a given type and amount of carbon based fuel.
Referring now to FIG. 3, this table shows calculated values for the amount of moisture removed per hour from ambient air for a hypothetical carbon combustion based power plant having a capacity on the order of 300 mW/unit. The values were calculated based on shown temperatures and Rh values of the ambient air. Different panels show data calculated for stoichiometric ratios of air to carbon based fuel (Left most panel); 5% excess air (center panel) and 25% excess air (right most panel). The condensate formed in this process comes chiefly from superheated vapor, therefore the condensate removed from the air can be used in lieu of de-ionized water.
Referring now to, FIG. 4, ideally, intake air is measured gravimetrically in order to set the optimal ratio of air to fuel for clean and efficient combustion. However, as a practical matter air is generally delivered to a furnace on a volumetric basis. In the combustion industry specifications for air handling equipment are generally given for air that has a temperature of 80° F. and Rh of 60%. When the ambient air temperature and Rh values exceed theses values the mass of the air supplied to the combustion zone may be inappropriate for complete combustion. When ambient air's temperature and Rh values are below the values for which the air handling equipment is specific the result may again be the delivery of sub-optimal amounts of oxygen and/or moisture to the combustion chamber, resulting in sub-optimal combustion.
In many systems the amount of intake air to be delivered to the combustion chamber is based on measurements made on the amount product produced by combustion. When the amount of intake air supplied to the ignition zone is based upon the amount of combustion products produced by the system the amount of intake air supplied to combustion may be sub-optimal. The result may be an increase in unburned hydrocarbon (UHB) waste in the fly ash, which subsequently increases the heat rate of combustion. One embodiment includes adjusting psychometric conditions of the air introduced into the ignition zone such that the amount of intake air better matches the gravimetric amount of oxygen required for the clean and efficient combustion of the carbon based fuel. In one embodiment the intake air is conditioned such that the volume of air is controlled to be within the air handling equipment's specifications. For example, if the air handling equipment is speced at 50° F. and 100% Rh and the ambient air is at 100° F., the devices and or methods according to various embodiments can be used to adjust the intake air to about 50° F. and 100% Rh, thereby ensuring delivery of a near stoichiometric amount of oxygen to the ignition zone.
Controlled, conditioned, combustion of intake air can greatly reduce the amount of NOx produced and emitted from the reaction. This is likely true because more precisely metering the amount of air in the reaction results in a more optimal match between the amount of air actually delivered to the reaction with the theoretical amount necessary for optimal combustion.
More precisely controlling the condition and amount of air in combustion lessens the amount of oxygen that is present at ignition to freely react with sulfur and molecules that include sulfur and that are presenting the combustion chamber. Hence, fuel is consumed more efficiently in balance with the optimum theoretical stoichiometric ratio of fuel to oxygen providing a cleaner more efficient born of the fuel.
Precisely controlling the condition and amount of intake air provides the means to regulate the rate of combustion by supplying more exacting control over the heat energy used for pre-heating the combustion air. Referring now to FIG. 5, for example, the heat required in the secondary intake air stream, according to one embodiment, is about 1040 BTU for conditioned air as compared to a calculated heat requirement of about 1,350 BTU for non-conditioned air at 200° F.
Still another advantage of controlling the temperature and Rh of the air used in combustion is the ability to control the wet bulb values of the fuel air mix at combustion. Adjusting the pressure and/or temperature of the air used in combustion can be used to control the volume of air in the reaction and thereby the oxygen/fuel ratio. Means that can be used to adjust the volume of intake air include both vapor compression and absorption refrigeration.
For example, when medium volatile bituminous coal is used as the fuel air in the combustion chamber that has a low wet bulb temperature has various advantages, including: reduced encrustation at the pre-heater, reduced wetting of soot and ash, higher steam temperature (because less heat is used to produce secondary products of combustion), lower heat rate, a reduction of the amount of power required for the on prime air handler and, a reduction in the amount of undesirable products of combustion produced such as NOx, SO₂, CO, excess stack heat, and CO₂.
Referring now to FIG. 6, as per a hypothetical heat value for a sample of coal including 13,041 Btu/# of coal, a hypothetical reduction of coal consumption is achievable by adjusting the amount of excess air from 25% to 5%. These calculations are based on delivering an optimal amount of oxygen in an optimal volume of air into the combustion chamber. The table also includes a calculation illustrating the amount of refrigeration (shown in tons/hr) required to condition ambient air with the physical values shown in the table. The temperature, pressure and or moisture content of the air is adjusted to deliver the stoichiometric amount of oxygen necessary for burning a given amount of coal having a given level of Btus per weight or mass of coal. Thus, optimizing the amount of air introduced into the combustion chamber based on the mass or weight of oxygen in the air can produce a significant savings in the amount of coal used to generate useful heat.
One embodiment is a device for the efficient burning of carbon based fuel. Referring now to FIG. 7, a diagram illustrating some parts of a combustion air handler. Various aspects of the device 10, includes conditioning coil 20 guide vanes 22; filter bank 24, condensate drain 26, demister 28 and insulated housing 30; Ambient air is taken into the housing 30, is filtered in filter bank 24, pre-compressed or pre-expanded in controllable guide vane 22. The guide vane 22 will be positioned remotely by the on-line analysis of the products of combustion, ambient temperature profile relative humidity, barometric pressure, temperature, composition of the fuel and the like. The condensing coil 20 will lower the dry bulb temperature to a state of saturation. In one embodiment chillate produced from refrigeration (not shown) provides for the means to remove heat and/or to heat the air stream through the coils when ambient temperature drops below 40° F. Conditioned air 40 will be drawn through coil 20 by an exiting force draft fan (not shown) and/or adiabatic blower configured to the primary and secondary air requirement. Not shown is the soot blowing air stream, a high velocity air stream delivered intermittently during combustion to help control the build-up of soot on various components of the device. Typically soot blowing air is introduced after the secondary air source immediately before the combustion chamber. The gravity flow of condensate will be directed to condensate sump 26 where it will be gathered. In one embodiment the water collected from condensate sump 26 can be used as a source of deionized water or the like. Demister 28 will absorb carryover water and drain it back to condensate sump 26. In one embodiment the fabricated housing 30 will be structurally framed so that fit is self-supporting but attached to the existing combustion air intake. The housing will be insulated and have man hold accesses framed so as to facilitate inspection and service.
Another embodiment provides the means to condition the intake combustion air (both primary and secondary) by refrigeration. Lowering the temperature of intake air can condense out superheated vapor, lower the wet bulb values of the air so as to dehydrate and demist the intake air. The intake ambient air can be filtered at the intake where adherent moisture is demisted and drained. The filter can be a multi-zone filter bank and can be either cellular or dynamic. The filter mechanism may be racked and mounted upstream from a pre-compression or expansion system of motorized vanes that can increase or decrease air flow to adjust the barometric pressure of the intake air. The positioning of the guide vane can be automated and controlled by upstream temperature, pressure and moisture sensing system configured to a computer which calculates optimized conditions and signals the system to adjust the intake air's physical parameters accordingly. In one embodiment the automated guide vane controller can be overridden by a plant operator.
In one embodiment a rack of condensing coils is located downstream from at least one guide vane. In one embodiment theses coil are connected to pass chillate in the amount needed to condense out all superheated vapor from the chillate. In one embodiment the chillate has an EWT of about 45° F. to a LWT of about 55° F. Chillate flow temperature will be regulated so to be weather protected when dry bulb temperature drops to 40° F. In one embodiment a supplemental heater will engage the chillate and maintain a temperature of at least 40° F. or above freezing. The chillate or heat transfer fluid can be of any commercially available type suitable for this application, including for example, but not limited to Dow Chemical's DOW THERM product. Downstream from the conditioning coils will be a condensate sump configured to the slope of the housing flooring so as to drain off surplus condensate through, for example, a pipe. In one embodiment, located further downstream will be a rack of demisters configured and shaped to augment the removal of any carry-over condensate.
In still another embodiment the device includes an optional pre-heater coil that can condition the intake air to remove excess water adhering to coal feed into the pulverizer.
Another embodiment is an air handler structured so as to join onto existing primary, secondary intake air and soot blowing air systems. The housing can be constricted so as to stand independently, this may facilitate attaching this type of housing to a preexisting air handling system. In one embodiment at least one component of the air handler is coated with an insulating material.
While the novel technology has been illustrated and described in detail in the figures and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the novel technology are desired to be protected. As well, while the novel technology was illustrated using specific examples, theoretical arguments, accounts, and illustrations, these illustrations and the accompanying discussion should by no means be interpreted as limiting the novel technology. All patents, patent applications, and references to texts, scientific treatises, publications, and the like referenced in this application are incorporated herein by reference in their entirety.

Claims

1. A device for conditioning air in carbon based fuel burning system, comprising:

an intake air chamber for conditioning ambient air;

a combustion chamber; and

at least one sensor for measuring physical parameters of air in said air intake chamber, wherein the intake air chamber can be adjusted so as to control the temperature and moisture content of ambient air drawn into said chamber, and wherein said chamber is positioned so as to feed air into the combustion chamber.

2. The device according to claim 1, wherein said intake air chamber includes a heat transfer coil.

3. The device according to claim 1, wherein said intake air chamber includes a device for removing water vapor to air in said intake air chamber.

4. A method for increasing the efficient of combustion, comprising the steps of:

providing an intake air condition chamber, and

supplying at least one sensor that measures the physical characteristic of ambient air; and

a computer which calculates and adjust conditions within said intake air conditioning chamber so as to optimize combustion, wherein said intake air conditioner is located between a source of ambient air and a combustion chamber and wherein said optimal combustion condition includes a substantially optimum stoichiometric ratio of carbon based fuel, oxygen and water in the combustion chamber.

5. A method for increasing the efficacy of hydrocarbon combustion comprising the steps of:

conditioning intake air and soot blowing air; and

delivering conditioned intake air to a combustion chamber, wherein said combustion chamber includes at least one hydrocarbon based fuel, and said intake air delivered to said combustion chamber comprising about 2.67 pounds of oxygen per about 1 pound of carbon.

6. The method according to claim 5, wherein said conditioning includes adjusting at least one of the following parameters of said intake air, temperature, pressure, and Rh.