Stoves and furnaces – Liquid heater – Fluid fuel burner for other than top-accessible vessel
Reexamination Certificate
1999-09-30
2001-09-25
Price, Carl D. (Department: 3743)
Stoves and furnaces
Liquid heater
Fluid fuel burner for other than top-accessible vessel
C122S031200
Reexamination Certificate
active
06293277
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a novel sludge treatment system using a two-step heat recovery submerged combustion. More particularly, this invention relates to a novel submerged combustion sludge treatment and pasteurization system with a lowered self-cooling combustion chamber and a two-stage heat recovery design. The system can be installed singly or in combination with other similar two-stage heat recovery submerged combustion systems to heat large quantities of municipal sludges and liquid-solid solutions.
BACKGROUND OF THE INVENTION
Recently enacted United States federal law requires that municipal sludges be pasteurized to remove harmful pathogens. The sludge must be passed through a non-agitation type retention tank and held at a temperature of at least 158° F. for at least 30 minutes. Heating large quantities of sludge to 158° F. for a period of 30 minutes presents a difficult and challenging engineering problem.
Submerged combustion heating is a method whereby hot products of combustion are forced through a liquid or liquid-solid mixture to heat the liquid or liquid-solid mixture. A major advantage of this heating system is that the heat exchange occurs directly between the hot gaseous products of combustion and the liquid or liquid-solid. Thus there is no interface that interferes with heat exchange. In a submerged combustion system, the hot combustion products are generated by a flame which is typically fuelled by a combination of air and natural gas. The flame generates hot combustion gases which contact the liquid or liquid-solid to be heated, but the flame itself does not come into contact with the liquid or liquid-solid.
This submerged combustion technology differs from conventional heat exchange methods such as immersion tube heating where the heat exchange is indirect through a solid interface and the products of combustion are exhausted directly to the atmosphere, rather than being forced through the liquid. Submerged combustion can be utilized to heat liquids with overall system efficiency greater than 90%. Conventional hot water boiler indirect heating systems have an efficiency of about 80%. Immersion tube heating systems are relatively low performers and have an efficiency of about 70%.
In applications where separation of components by distillation or absorption is required, submerged combustion heating can be applied to generate liquid or liquid-solid temperatures up to about 195° F. This is not much below the boiling point of water, and is applicable to most industrial and domestic liquid or liquid-solids heating applications.
In addition to high efficiency, submerged combustion heating systems are advantageous because they maintain a uniform temperature throughout the liquid or liquid-solid in which the submerged combustion is conducted. This is because the hot gaseous combustion products pass rapidly through the liquid and keep the liquid in constant agitation, thereby distributing heat evenly. Submerged combustion heating systems are also suitable for heating contaminated liquids, or liquids with low medium or high solids contents. Expenses are usually lower than with other heating systems because the submerged combustion heating can be conducted in a liquid holding tank which can operate at ambient pressures, thereby eliminating the need to be pressurized. Unlike boiler heating applications, a certified operating engineer is not required to operate a submerged combustion heating system.
A typical industrial application for a submerged combustion system is a municipal effluent holding and treatment pond, which can include maintenance of pond temperatures to ensure continuous high level of biological degradation especially in regions that experience extreme seasonal temperature changes, and in other cases, elevated temperatures to pasteurize the effluent.
The applicant is the assignee of one or more of the inventors herein and therefore the owner of the following patents relating to a submerged combustion heating system:
1. U.S. Pat. No. 5,606,965, granted Mar. 4, 1997 entitled “Submerged Combustion System”;
2. U.S. Pat. No. 5,615,668, granted Apr. 1, 1997, entitled “Apparatus for Cooling Combustion Chamber in a Submerged Combustion Heating System”; and
3. U.S. Pat. No. 5,636,623, granted Jun. 10, 1997, entitled “Method and Apparatus for Minimizing Turbulence in a Submerged Combustion System”.
4. U.S. Pat. No. 5,032,230, Sheppard, discloses a system for evaporating large quantities of liquid using a vacuum system.
The subject matter and contents of the first three aforementioned U.S. patents is incorporated herein by reference.
SUMMARY OF THE INVENTION
The invention is directed to a sludge treatment apparatus including a two-stage submerged combustion heating system comprising: (a) a sludge inlet line; (b) a heat exchanger through which the sludge inlet line passes; (c) a first liquid holding vessel, said first holding vessel having a liquid inlet from the heat exchanger and a liquid sludge outlet connected to the heat exchanger, and an exhaust gas outlet; (d) a combustion chamber positioned in the interior of the first vessel, at least the bottom portion of the combustion chamber being located below the top elevation of the vessel and in the liquid sludge in the first tank; (e) fuel and air conveyors associated with the combustion chamber for conveying fuel and air into the interior of the combustion chamber, said fuel and air being ignited to create a combustion flame inside the combustion chamber, said flame not touching the interior walls of the combustion chamber or the liquid, said flame generating a hot combustion gas; (f) a plurality of openings located in the combustion chamber for enabling the hot combustion gas to be exhausted from the interior of the combustion chamber into liquid sludge in the first vessel below the level of liquid sludge in the first vessel and heating the liquid sludge in the first vessel; (g) a second liquid sludge holding vessel connected to the first vessel and holding liquid sludge; (h) a hot air chamber positioned in the interior of the second liquid sludge vessel and connected with the first vessel, said hot air chamber being connected to and receiving hot combustion gas from the first vessel and exhausting the hot combustion gas through the liquid sludge in the second liquid sludge holding vessel and heating the liquid in the second vessel; and (i) an outlet line connecting an outlet of the heat exchanger to a process downstream.
The submerged combustion system can include a first liquid level control for controlling level of liquid in the first holding vessel so that the level of the top of the liquid sludge is above the plurality of openings in the combustion chamber, and above the liquid sludge inlet but at or below the level of the liquid sludge outlet, and a liquid level control for controlling level of liquid in the second holding vessel, said hot combustion gas transferring heat from the hot combustion gas to the liquid in the first vessel and the liquid in the second vessel. A weir can prevent hot combustion gas from exiting the first vessel through the liquid outlet. The plurality of openings can be located in the lower region of the combustion chamber and can horizontally encircle the periphery of the combustion chamber.
The first vessel can be a hollow cylindrical vessel, having vertical walls, a first bottom, a first top and a first vertical longitudinal axis, and the combustion chamber can be a smaller hollow cylindrical vessel which can have vertical walls, a second bottom, a second top, a second vertical longitudinal axis coincident to the first longitudinal axis of the first cylindrical vessel, and the plurality of openings is located in the lower region of the smaller cylindrical vessel. The top portion of the smaller cylindrical vessel can have a truncated conical shape. The openings can be vertical slots in the lower region of the combustion chamber.
Liquid level in the first vessel can be maintained at a level above the first bottom of the first vessel and above the bottom
Jachniak Joseph Lech
Panz Eric Leopold
Panz Steven Eric
Inproheat Industries Ltd.
Oyen Wiggs Green & Mutala
Price Carl D.
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