WO2000015558A1

WO2000015558A1 - Thermal evaporation apparatus

Info

Publication number: WO2000015558A1
Application number: PCT/US1999/019852
Authority: WO
Inventors: Danny R. Bolton; James E. Bigham; David G. Smith
Original assignee: Wis-Tex Technologies, L.L.C.
Priority date: 1998-09-10
Filing date: 1999-08-30
Publication date: 2000-03-23
Also published as: AU5699099A

Abstract

Thermal evaporation apparatus (10) for wastewater includes an evaporation tank (12) having an upper water level end (L1) and a lower water end (L2), where the water level in the upper water level end is maintained at a higher water level than the water level in the lower water level end. At least one gas-fired burner (16) is connected to a vertical combustion chamber (26), with the vertical combustion chamber (26) extending through the upper water level end of the evaporation tank (12), and with a horizontal sparger tube (28) connected to the vertical combustion chamber (26) and extending through the lower water level end (L2) of the evaporation tank (12).

Description

TITLE: THERMAL EVAPORATION APPARATUS

Field of the Invention

This invention relates to evaporators, and more particularly, to an evaporator for the

treatment of polluted water such as landfill leachate and landfill gas condensate.

Background Art The disposal of polluted wastewaters is of increasing concern due to ever tighter environmental regulations. Sources of such wastewaters are municipal landfills, petro¬

chemical industries, paper industries, food industries, agricultural operations, remedial clean¬

up activities, and general industrial sources.

In particular, various kinds of wastes are buried in landfills that are known to produce noxious gases and condensates as the wastes decompose. In addition, water from rain and

other sources percolates through the buried wastes, creating noxious leachates. These leachates are composed of a variety of chemicals, many of which are hazardous. Escaping gases and liquids from such landfills are recognized as sources of pollutants that present health and environmental hazards and must be collected and treated.

It is common to dispose of the noxious gases produced by a landfill by withdrawing these largely methane-based gases and burning them in flares or other types of gas

combustion devices. In most cases removal of the noxious gases from the landfill results in

the production of liquid condensates. These condensate liquids together with the leachate

liquids have traditionally been collected and hauled from the landfill site for disposal. This

process of disposal is itself regulated and expensive as evidenced by the large amount of attention that has been given to the transportation and safe disposal of industrial waste

liquids.

Prior art technology has been developed to deal with leachate and condensate disposal

and includes the evaporation of the liquid leachate/condensate in a gas-fired, direct contact evaporator, such as that taught in the patent to Young et al., U.S. Pat. No. 4,838,184. The

Young patent teaches an apparatus and method for combusting a portion of the landfill gases

and contacting a stream of the hot combustion products with the leachate liquids from the

landfill to vaporize a portion of the leachate liquids. A drawback of the Young apparatus is

its complexity and inefficiency, and the apparatus does not produce the desirable end result

pollutant-free water vapor and an easily disposed of concentrated solids sludge.

Similarly, the patent to Duesel, U.S. Pat. No. 5,342,482 discloses an evaporation

device for landfill leachate that has two zones, an evaporation zone in the upper section of the apparatus and a quiescent solids-settling zone in the lower section of the apparatus. This

enables the simultaneous carrying out of evaporation and solids settling. It has been found, however, that the percentage of solids in typical wastewater streams is actually quite low, such that only after long periods of evaporation is it necessary to remove solids. In this

situation it is preferable to merely pause the evaporation process for an appreciable period o time to permit solids to settle and then be removed. This non-simultaneous batch approach t

evaporation and solids settling avoids the overly complex dual-zone apparatus of the Duesel

patent.

Thermal efficiency has been found to be a key factor in the design of successful

evaporator systems. Where landfill gas is the fuel, the fuel is essentially of no cost. The low BTU nature of the gas, however, requires that as much as possible of what little energy is

available be utilized for evaporation. Where purchased natural gas or propane gas is used as

the fuel, expense becomes of primary concern and thermal efficiency is again a key factor.

It would be therefore be desirable to have a disposal system that would overcome

these and other limitations of the prior art systems. That is, it is desirable to have a disposal

system which can efficiently and lawfully dispose of all leachate and gas condensates

produced from any landfill in an apparatus, and which produces an easily disposed of solids

sludge, while releasing only substantially pollutant-free water vapor which can be readily

discharged in compliance with air quality standards and regulatory permits governing

landfills.

Summary of the Invention

The present invention provides a thermal evaporation apparatus having a dual level

influent system to optimize thermal efficiency. The evaporation apparatus of the present invention is designed to efficiently evaporate primarily wastewaters generated from any

industrial, commercial or municipal source.

The present invention utilizes submerged combustion technology. This is a highly- efficient, proven process where the combustion of the air and gas occurs below the surface of the liquid being evaporated. The hot air stream is also released below surface and into direct

contact with the liquid being evaporated.

A key feature of the invention is that the evaporation tank design allows for two different influent liquid levels to be maintained in the unit at all times while it is operating.

The system burners and gas train are designed to operate on propane gas, natural gas, landfill gas or fuel oil. The tubes into which the burners are fired are comprised of two sections, a

vertical combustion chamber and a horizontal sparger tube. The burners are coupled to the

vertical combustion chambers in an upper water level end of the evaporation tank. The

vertical combustion chambers are sized to ensure that substantially all of the combustion of

the air/gas mixture occurs in the vertical combustion chambers. The water is maintained at a higher level in the upper water level end of the

evaporation tank to more efficiently transfer heat to the water for evaporation and, as an

additional benefit, keep the flames from overheating the combustion chambers. The burner

plumes can extend a significant distance from the burners, and it is desirable to have the

plumes entirely below water level so that heat can be applied to the surrounding water

through conduction and direct contact with the walls of the vertical combustion chambers. In

addition, the walls, which otherwise would glow cherry red from the heat, are kept at a low temperature to prolong their life. The higher level of water is determined by an over-flow

weir that allows water and vapor to flow into a lower water level section of the system.

The vertical combustion chambers are connected to horizontal sparger tubes that extend through a fixed wall that divides the upper and lower water level sections. The sparger tubes have hot gas outlet ports positioned along the bottoms thereof through which the hot

gasses from the burners are released into the liquid. It is these hot gasses that heat the water to the vaporization temperature. The combustion gasses and vaporized water exit the tank

through the exhaust stack. A predetermined water level is maintained at several inches above

the tops of the sparger tubes in this section by a level sensor.

The bottom of the tank is sloped to allow any solids that may be contained in the

waste water to settle into a trough when the unit is not evaporating. Located in the trough is a

horizontal screw auger that transfers the solids to an external discharge conveyor which has a

solids discharge port that is higher than the liquid level maintained in the lower water level end of the tank. The bottom of the tank on the upper water level end also slopes to a port

above the trough. A water recirculation pump pulls water from the lower water level end and

discharges it into the upper water level end. The port is sized to allow only a portion of the

total amount of water from the pump to be drained here. The remainder of the water will flow

over the weir. Brief Description of the Drawings

A more complete understanding of the invention and its advantages will be apparent

from a review of the Detailed Description in conjunction with the following Drawings, in

which:

FIGURE 1 is a partially broken away schematic side view of the apparatus of the

present invention;

FIGURE 2 is a sectional view of the apparatus taken along lines 2-2 in FIGURE 1 ;

and

FIGURE 3 is a sectional view of the apparatus taken along lines 3-3 in FIGURE 2.

Detailed Description

Referring initially to FIGURES 1-3, where like numerals indicate like and

corresponding elements, thermal evaporation apparatus 10 includes an evaporation tank 12 that allows for a higher influent liquid level LI and a lower influent liquid level L2 to be

maintained in the unit at all times while it is operating. The system burners 16 are fed by a

source of fuel (not shown) that can be propane gas, natural gas, landfill gas or fuel oil.

Blower 18 provides combustion air from inlet 20 through manifold 22.

The tubes 24 into which the burners are fired are each comprised of two sections, a vertical combustion chamber 26 and a horizontal sparger tube 28. The burners 16 are

coupled to the tops of vertical combustion chambers 26 in the upper water level end 30 of

evaporation tank 12. The vertical combustion chambers 26 are sized to ensure that substantially all of the combustion the air/gas mixture occurs in the vertical combustion

chambers 26.

The water is maintained at the higher level LI in upper water level end 30 to absorb heat from the vertical combustion chambers 26, and thereby more efficiently receive heat for evaporation, and also to keep the flames from overheating the combustion chambers 26. The higher level LI of water is determined by an over-flow weir 31 that allows water and vapor to

flow into the lower water level end 34 of the evaporation tank 12.

The vertical combustion chambers 26 are connected to the horizontal sparger tubes 28 that extend through a fixed wall 36 that divides the upper and lower water level sections 30, 34. The sparger tubes 28 have hot gas outlet ports 38 (FIGURE 2) positioned along the bottoms 40 thereof through which the hot gasses from the burners 16 are released into the

liquid 42 from upper level section 30. It is these hot gasses that heat the water to the

vaporization temperature. The combustion gasses and vaporized water exit the tank 12

through the exhaust stack 44 and are essentially pollutant free. The predetermined water level L2 is maintained at several inches above the tops 46 of the sparger tubes 28 in this end

32 of the tank 12 by a level sensor 48.

The bottom 50 (FIGURES 2 and 3) of the tank 12 is sloped to allow any solids that

may be contained in the waste water to settle into a trough 52 when the unit is not evaporating. Located in the trough 52 is a horizontal screw auger 54 that transfers the solids

to an external discharge conveyor 56 which has a solids discharge port 60 that is higher than

the liquid level L2 maintained in the lower water level end 32 of the tank 12. A collection bag 62 collects the discharged solids, which are in the form of an easily disposed of sludge. The bottom 64 of the tank 12 at the upper water level end 30 also slopes to a port 66 above the trough 52. A water recirculation pump 68 pulls water from the lower level end 32 and discharges it into the upper water level end 34. The port 66 is sized to allow only a portion of the total amount of water from the pump 68 to be drained back into lower water level section 32 through trough 52. The remainder of the water flows over weir 31.

While the invention has been described and illustrated in the form of apparatus having two burners, combustion chambers and sparger tubes, it will be appreciated that the invention can readily be utilized in a device having only one each of these elements, or more than two of these elements, as a matter of design choice. Whereas, the present invention has been described with respect to a specific embodiment thereof, it will be understood that various changes and modifications will be

suggested to one skilled in the art and it is intended to encompass such changes and modifications as fall within the scope of the appended claims.

Claims

We claim:

1. Thermal evaporation apparatus for wastewater, comprising:

an evaporation tank having an upper water level end and a lower water level end, where the water level in the upper water level end is maintained at a higher water level than the water level in the lower water level end; and at least one gas-fired burner connected to a vertical combustion chamber, the vertical combustion chamber extending through the upper water level end of the evaporation tank,

and with a horizontal sparger tube connected to the vertical combustion chamber and extending through the lower water level end of the evaporation tank.

2. The apparatus of Claim 1 with a water recirculation pump in fluid

communication with the evaporation tank upper water level end and lower water level end

for transferring water from the lower water level end to the upper water level end.

3. The apparatus of Claim 1 with the water level in the upper water level end

maintained by a fixed weir.

4. The apparatus of Claim 1 with the lower water level end of the evaporation tank having a bottom sloping to a trough, with an auger in the trough for solids removal.

5. The apparatus of Claim 4 with the upper water level end of the evaporation

tank having a port in fluid communication with the auger.

6. Thermal evaporation apparatus, comprising: an evaporation tank having a dual level influent system for maintaining two different influent water levels to be maintained in the apparatus unit at all times while the apparatus is operating, the evaporation tank having an upper water level end and a lower water level end; at least one submerged combustion system, where combustion of fuel occurs below

the surface of water being evaporated, such that a hot combustion gas stream is released below the surface and into direct contact with the water being evaporated; and the submerged combustion system including a vertical combustion chamber and a horizontal sparger tube, the burner coupled to the vertical combustion chamber in the upper

water level end, and the vertical combustion chamber being sized such that substantially all

combustion of the fuel occurs therein.

7. The apparatus of Claim 6 with the submerged combustion system including at

least one burner to operate on fuel selected from the group consisting of propane gas, natural

gas, landfill gas or fuel oil.

8. The apparatus of Claim 6 with the level of water in the upper water level

section of the evaporation tank being determined by an over-flow weir that allows water to flow into the lower water level section of the evaporation tank.

9. The apparatus of Claim 6 with the vertical combustion chamber being connected to the horizontal sparger tube through a fixed wall that divides the upper and lower water level sections.

10. The apparatus of Claim 6 with the sparger tube having hot gas outlet ports

positioned along the bottom thereof through which the hot gasses from the burner are

released into the water.

11. The apparatus of Claim 6 with an exhaust stack over the lower water level

section of the evaporation tank for the release of combustion gasses and vaporized water.

12. The apparatus of Claim 6 with a predetermined water level being maintained above a top of the sparger tube by a level sensor.

13. The apparatus of Claim 6 with the evaporation tank lower water level end

having a bottom being sloped to allow solids to settle into a trough when the unit is not

evaporating.

14. The apparatus of Claim 13 with a horizontal screw auger in the trough that

transfers the solids to an external discharge conveyor having a solids discharge port that is higher than the liquid level maintained in the lower water level end of the tank.

15. The apparatus of Claim 6 with the evaporation tank lower water level end having a bottom being sloped to a port to allow solids to settle into a trough when the unit is not evaporating.

16. The apparatus of Claim 15 with a horizontal screw auger in the trough that transfers the solids to an external discharge conveyor having a solids discharge port that is higher than the liquid level maintained in the lower water level end of the tank.

17. The apparatus of Claim 6 with a water recirculation pump for transferring water from the lower water level end to the upper water level end.

18. The apparatus of Claim 17 with the evaporation tank lower water level end having a bottom being sloped to a port to allow solids to settle into a trough when the unit is not evaporating, the port being sized to allow only a portion of the total amount of water from

the pump to be drained therethrough and the remainder of the water being forced to flow over

a weir.

19. Thermal evaporation apparatus, comprising:

an evaporation tank having a dual level influent system for maintaining two different influent water levels to be maintained in the apparatus unit at all times while the apparatus is operating, the evaporation tank having an upper water level end and a lower water level end; at least one submerged combustion system, where combustion of fuel occurs below the surface of water being evaporated, such that a hot combustion gas stream is released below the surface and into direct contact with the water being evaporated; the submerged combustion system including at least one burner to operate on fuel selected from the group consisting of propane gas, natural gas, landfill gas or fuel oil; the submerged combustion system including a vertical combustion chamber and a

horizontal sparger tube, the burner coupled to the vertical combustion chamber in the upper

water level end, and the vertical combustion chamber being sized such that substantially all combustion of the fuel occurs therein; the level of water in the upper water level section of the evaporation tank being

determined by an over-flow weir that allows water to flow into the lower water level section

of the evaporation tank;

the vertical combustion chamber being connected to the horizontal sparger tube

through a fixed wall that divides the upper and lower water level sections; the sparger tube having hot gas outlet ports positioned along the bottom thereof

through which the hot gasses from the burner are released into the water;

an exhaust stack over the lower water level section of the evaporation tank for the release of combustion gasses and vaporized water;

a predetermined water level being maintained above a top of the sparger tube by a

level sensor; the evaporation tank lower water level end having a bottom being sloped to allow solids to settle into a trough when the unit is not evaporating; a horizontal screw auger in the trough that transfers the solids to an external discharge conveyor having a solids discharge port that is higher than the water level maintained in the lower water level end of the tank; the evaporation tank upper water level end having a bottom being sloped to a port above the trough; and a water recirculation pump for transferring water from the lower water level end to the

upper water level end, the port being sized to allow only a portion of the total amount of water from the pump to be drained therethrough and the remainder of the water being forced to flow over the weir.