WO2001061247A1

WO2001061247A1 - A full-scale automated system for the destruction of air pollutants originating from wastewater treatment plants

Info

Publication number: WO2001061247A1
Application number: PCT/GR2001/000010
Authority: WO
Inventors: Nicholas P. Pittas
Original assignee: Pittas Nicholas P
Priority date: 2000-02-15
Filing date: 2001-02-15
Publication date: 2001-08-23
Also published as: CY1106953T1; PT1409924E; EP1409924B1; AU2001232142A1; EP1409924A1; ES2291292T3

Abstract

The full-scale automated system for the destruction of air pollutants originating from wastewater treatment plants, consists of a gas collector with convex surface, an electric automatic gas exhauster at the top of the collector, ventilator or one-direction valves from outside to the dome inlet based on the external perimeter of the gas collector and tubes which route the gases to the specially modified incinerator, where the gaseous emissions are burned by a fuel-gas (usually LPG), with the simultaneous generation of limited thermal energy.

Description

A FULL-SCALE AUTOMATED SYSTEM FOR THE DESTRUCTION OF AIR POLLUTANTS ORIGINATING FROM WASTEWATER TREATMENT

PLANTS.

The proposed system is a full-scale automated system for the destruction of air pollutants originating from wastewater treatment plants. The system consists of one or more ventilators, depending on the application system (with or no recycling), a gas collector with convex surface-usually dome, tubes, compressor, sensors, specially modified incinerator, chimney, flow rate of LPG or another fuel.

The biomass consumes about 1 kg O₂/m³waste. As a result it requires a sufficient quantity of air for biomass growth and compound degaradion. The air (oxygen) enters the tank, partly through the bottom, via a compressor with a system of thin tubes and partly from the surface due to armospheric oxygen. Brush aerators will be used in order to transfer atmospheric oxygen to the waste.

On the dome top there is a ventilator, which absorbs the mal-odorous gases and routes them to the incinerator (with a pressure sensor in the dome) through tubes with two one-direction safety valves. The mixture of air and mal-odorous gases is originated from the waste degradation, the compressor air bubbles and the inlet fresh air from vent-holes (one direction from outlet to inlet) on the base of dome external perimeter. Given that the cost of one-direction valves is high, we could use two or more ventilators on the base of collector external perimeter, removing the valves and the ventilator on the top. We could also use recycling of the mixture of air and malodorous gases, setting a by-pass of the outlet gases from the dome through the compressor and the external perimetric ventilator, which will feed always fresh air on a regular basis, depending on the treatment plant capacity. The aim of the recycling is to reduce the required air quantity, though there is a limit for good biomass oxygenation. The economical assessment, the construction implementation and the fuel cost will result to the best of the above alternative solutions. The gas collector with convex surface is fitted air-tightly on the wastewater treatment tanks, in order to avoid gas leakage. It is manufactured by a light but resistant material.

Such a full-scale automated system for the destruction of air pollutants originating from wastewater treatment plants has not been applied. Municipal wastewater treatment plants and analogous industrial facilities generate air pollutants, including odors that are dispersed to the neighboring regions. Both the necessity to improve air quality, as well as the need to make wastewater treatment more acceptable, from a social point of view, mandate that a solution to this serious problem is found. The construction is very economical and effective for the protection of the atmospheric environment and the maintenance of an ecological balance, while one envisions significant side-benefits from the exploitation of the generated thermal energy through a specially modified incineration.

The automated system of polluted gases purification, based on a patent, includes the following units: 1 ) A gas collector with convex surface, by light and resistant material, which is suited tightly on the wastewater treatment tanks

2) An electric automatic gas exhauster

3) One or more ventilator(s) based on the external perimeter of the gas collector

4) One direction valves from outside to the dome inlet 5) A compressor

6) Tubes, which route the exhaust gases from the exhauster outlet to the specially modified incinerator, founded with one direction valves, sensors etc, as well as a tube from the dome outlet to the compressor inlet if recycling is implemented.

7) A specially modified incinerator LPG fuel enters the flame of the incinerator in order to achieve the combustion of the mal-odorous gases. The gases have passed through a heat exchanger (Labyrinth) for preheating, in order to achieve reduction of required combustion gas, LPG or natural gas or coal oil.

The incinerator and boiler consist of: a)"Labyrinth" The mal-odorous gases pass in counter-flow direction and are preheated. They also maintain the outer surface of the incinerator at low temperature. b)"Turbulent mixer" It enhances the turbulence and, as a result, the gas mixing. In this way, more effective gas incineration is achieved. c)"Flame splitter" A non-aerodynamic cone that makes the flame flow in a turbulent way and operates as if tearing the flame in order to make it spread in a longer radial. d) "Catalyst" A catalyst could be optionally used to achieve better temperature conditions. This, however, would raise the cost of the project. As a result, the use of the catalyst is only to be examined on an economic basis. e) "Complementary thermal converter" An additional thermal converter can be placed in the same incinerator, from which, hot water or steam can be produced, in quantities that are proportional to the capacity of the biological treatment unit. In this way, the small need for heating can be satisfied and more turbulence can be provoked for full combustion. f) "Lighter" It is a system of igniting the fuel and is connected automatically to the sensors, through which, the LPG is provided and combusted. g) "Fire resistant obstacle" A fire resistant obstacle can be placed between the incinerator and the chimney in order to reduce the heat loss from the out-going gases.

This is the reason why the hinder part of the incinerator is constructed like an orifice. h) "Chimney" The combustion products come out of the chimney i) "Fuel tank" The fuel to be used is LPG. The content of the combustion gas products can be determined through a gas analyzer, and the flow rate of the LPG can be regulated in order to achieve almost perfect combustion. The quantities of the out-coming gases are expressed as parts per billion.

8) Heaters, which are the necessary stabilizers of the relative humidity in the inner curved surface to prevent problems in the operation of the gas exhauster or the ventilator

The whole construction is to be equipped with sensors and fully automated. The construction is very economical and necessary for the protection of the environment and the maintenance of the ecological balance, with the benefits from the production of the thermal energy.

Figure 1 Collector Figure 2 Collector + Gas Exhauster Figure 3 Collector + Gas Exhauster + one-direction Valves Figure 4 Collector + Gas Exhauster + Ventilator + one-direction Valves + Compressor and the suitable tubing if recycling is implemented Figure 5 : Collector + Gas Exhauster + Ventilator + 95 one-direction Valves + Compressor and the suitable tubing if recycling is implemented + tubing from the dome outlet to the incinerator Figure 6 : Collector + Gas Exhauster + Ventilator + one-direction Valves + Compressor 100 and the suitable tubing if recycling is implemented + tubing from the dome outlet to the incinerator + Incinerator and Boiler Figure 7 : Collector + Gas Exhauster + Ventilator + one-direction Valves + Compressor 105 and the suitable tubing if recycling is implemented + tubing from the dome outlet to the incinerator + Incinerator and Boiler + Fuel tank + Chimney The Figure 8 shows the incinerator and boiler parts: Figure 8. A : Labyrinth 110 Figure 8. B : Turbulent mixer

Figure 8.T : Labyrinth + Turbulent mixer + Flame splitter Figure 8.Δ : Lighter

Figure 8.E : Labyrinth + Turbulent mixer + Flame splitter + Conical Flame Figure 8. Z : Labyrinth + Turbulent mixer + Flame splitter + Conical Flame 115 + Catalyst + Complementary Thermal Converter + Fire resistant obstacle

EXAMPLE 1

Application of the patent to a hotel (200 beds) wastewater treatment plant

The composition of air pollutants from these wastewater treatments plants typically 120 include:

• Hydrogen sulfide -H₂S (5.000-50000ppb),

• Methyl mercaptan -CH₃SH (100-lOOOppb),

• Dimethyl trisulfide- (CH₃)₂S₃ (200-2000ppb),

• Dimethyl tetrasulfide-(CH₃)₂S₄ (20-200ρpb), 125 • Dimethylsulfιde-(CH₃)₂S (200-2000ppb),

• Dimethyl disulfide- (CH₃)₂S₂ (1000-5000ppb),

• Ammonia-NH₃ (O-lOOOOppb),

• Carbon disulfιde-CS (20-200ppb).

The chemical combustion reactions of the above compounds are:

130 Hydrogen sulfide H₂S +3/2 O₂ H₂O + SO₂

Methyl mercaptan CH₃SH + O₂ SO₂ + CFL

Dimethyl trisulfide (CH₃)₂S₃ + 3O₂ 3SO₂ + C₂H₆

Dimethyl tetrasulfide (CH₃)₂S₄ +4O₂ 4SO₂ + C₂H₆

C₂He +7/2 O₂ 2CO₂ + 3H₂O

135 Dimethylsulfide (CH₃)₂S + O₂ SO₂ + C₂H₆

Dimethyl disulfide (CH₃)₂S₂ + 2O₂ 2SO₂ + C₂H₆

Ammonia- H^ 2NH₃ + 5/2 O₂ 2NO + 3H₂0 + 140Kcal

Carbon disulfide CS₂ +30₂ CO₂ +2SO₂

Gas C_xH_y +(x+(l/4)y) O₂ xCO₂ + (y/2)H₂0 + energy

140 The dome (a convex surface which is fitted air-tightly on the wastewater treatment tanks) will be constructed out of iron sheet 6 mm, in order to avoid leakage due to the welding of the iron sheets.

The biomass consumes 1 kg O /m waste and about 670 'm air/day (28 m /h) are required. Based on this consideration, a dimensioning of the construction will be

145 done (with the ventilator on the dome base and one stand-by) with uniform air distribution on the dome base, through a perimetric channel for oxygenation of the biomass, in order to achieve degradation in the inner part of the dome.

For dimensioning of the gas exhauster (ventilator) at the top of the dome (convex surface), the required quantity of air is the sum of 280m" Pa and the air of 150 compressor (m³/h) that is necessary for biomass oxygenation. The air (oxygen) will be bubbled with a system of thin tubes at the bottom of the plant.

The dimensioning of the tubes and the setting of one-direction valves will follow.

The dimensioning of the incinerator will be based on the gas-mixture velocity 155 (mal-odorous gases + LPG) from the turbulent mixer in order to avoid flame extinction. A catalyst could be used to achieve conversion at lower temperatures.

All system operations will involve sensors and it will be automatically controlled by PLC.

The system will include portable analytical equipment for monitoring of all 160 the polluting gases and and the flow rate of the LPG can be regulated in order to achieve almost perfect combustion.

We estimate that the required LPG cost is 1280 drachmas/day (3,75 Euro), while the cost using recycling is estimated at 850 drachmas/day (2,49 Euro).

Claims

PATENTS CLAIMS165 1. The full-scale automated system for the destruction of air pollutants, originating from wastewater treatment plants consists of a collector with convex surface (Fig.l), an electric automatic gas exhauster at the top of the collector (Fig 2), one-direction valves from outside to the collector inlet based on the external perimeter of the gas collector (Fig. 3), ventilator based on the external perimeter of the gas collector (Fig170 4) and tubes which route the exhaust gases from the collector outlet to the specially modified incinerator (Fig 5), where the gaseous emissions are burned by a fuel-gas (usually LPG) (Fig 6) in the reservoir (Fig 7). The incinerator-boiler consists of: "Labyrinth" (Fig. 8.A), "Turbulent mixer" (Fig 8.B), "Labyrinth" + "Turbulent mixer" +"Flame splitter" (Fig. 8 T), Lighter (Fig. 8.Δ), "Labyrinth" + "Turbulent175 mixer" +"Flame splitter" + "Conical Flame" (Fig. 8.E), "Labyrinth" + "Turbulent mixer" +"Flame splitter" + "Conical Flame" + "Catalyst" + "Complementary thermal converter" + "Fire resistant obstacle" (Fig. 8.Z). The combustion products come out through the chimney (Fig. 7).2. According to the claim 1, the above system includes a gas collector with convex 180 surface, an electric automatic gas exhauster on the top of the collector, air inlet valves from outside to the dome inlet, ventilator based on the external perimeter of the gas collector, tubes which route the mal-odorous gases, via fitments of the incinerator- boiler "Labyrinth" (thermal converter), turbulent mixer where the gases are burned, by a fuel-gas (usually LPG) in the reservoir, in a conical flame. The combustion 185 products pass through the incinerator and catalyst and heat the complementary thermal converter for thermal energy production. The combustion products come out through the chimney.3. According to the claims 1 and 2, the above system includes a dome collector with convex surface, ventilator(s) and one direction valves based on the external perimeter190 of the gas collector, an electric automatic gas exhauster on the top of the collector, tubes which route the mal-odorous gases to the specially modified incinerator. The gases are burned by a fuel-gas (usually LPG) in the reservoir.4. According to the claims 1, 2 and 3, the full-scale automated system for the destruction of air pollutants originating from wastewater treatment plants operates195 with recycling too, and includes a compressor which routes the outlet gases from the collector to the wastewater treatment plant, ventilator(s) or one direction valves based on the external perimeter of the gas collector, an electric automatic gas exhauster on the top of the collector (Fig. 7), tubes which route the mal-odorous gases, via fitments of the incinerator-boiler "Labyrinth" (thermal converter), turbulent mixer where the gases are burnt, by a fuel-gas (usually LPG) in the reservoir, in a conical flame. The combustion products pass through the incinerator and catalyst and heat the complementary thermal converter for thermal energy production. The combustion products come out through the chimney. AMENDED CLAIMS[received by the International Bureau on 19 July 2001 (19.07.01) original claims 1 - 14 replaced by new claims 1 - 12 (1 page)]

1. A system for the destruction of air pollutants originating from a wastewater treatment plant, comprising: a dome-shaped gas collector; a gas exhauster disposed at the top of the gas collector; and an incinerator communicating with said gas exhauster; the incinerator being arranged to burn collected gases by means of a flame produced with the help of a fuel.

2. The system of claim 1, wherein the incinerator uses a gas fuel, such as LPG, or an oil fuel.

3. The system of claim 1, wherein the incinerator includes a flame splitter, especially a flame splitter arranged to produce a conical flame.

4. The system of claim 1, wherein the incinerator includes a catalytic converter.

5. The system of claim 1, wherein the incinerator includes a heat exchanger for heating collected gases.

6. The system of claim 1 , wherein the incinerator includes a mixer arranged to enhance the turbulence.

7. The system of claim 1, wherein a ventilator is provided for routing collected gases to the incinerator.

8. The system of claim 1, wherein a ventilator is provided in the gas exhauster or at the base of the gas collector, in particular externally thereof.

9. The system of claim 1, wherein means is provided for recycling collected gases to the wastewater treatment plant.

10. The system of claim 1, wherein the gas collector is fitted on a tank of the wastewater treatment plant.

11. The system of claim 1, wherein the gas collector is provided with an air inlet allowing outside air to enter the gas collector.

12. A method for the destruction of air pollutants originating from a wastewater treatment plant, comprising: collecting gases from a tank of the wastewater treatment plant; producing a flame with the help of a fuel; and incinerating collected gases by means of said flame.