Patent Application
20100129895
1. Field of Invention
The invention relates to an apparatus and process for treating air streams to remove pollutants. More particularly it relates to a system that allows for remediation of multiple contaminants by contaminant-specific remediation organisms having differing pH and moisture needs, the continuous flow process being performed within an internally segmented unitary housing in which there is no fluid connection between the sectional treatment chambers.
2. Description of the Relevant Prior Art
Vaporous pollutants, which are frequently toxic or corrosive or both, are created in a multiplicity of municipal, commercial and agricultural processes and become part of output airstreams. Treatment of these output airstreams to strip out the pollutants is important to human health, to prevent damage to equipment, to protect the environment and to provide odor control.
The earliest methods used to deal with these pollutants were by physical and chemical processes. The physical processes unfortunately created large amounts of contaminated waste materials that then had to be dealt with. The chemical treatment methods that replaced physical decontamination are well established and reliable, however, they involve the use of hazardous chemicals and are associated with the need for increased safety features that increase the footprint and the operating costs of the units.
These drawbacks led to the development of biological treatment of air streams that has proven itself to be effective, safe and cost effective. Such biological treatment systems are capable of treating high flows of contaminated gas having high inlet concentrations of pollutants.
A typical biological treatment system involves passing the contaminated air stream through an inert, porous media base that has been inoculated with and supports the growth of specific microorganisms. The contaminated air passes over the organisms which feed on and convert the pollutants into innocuous compounds, thus removing the odor and other undesirable components and allowing the release of remediated air.
The whole process taking place within a containment structure which serves as a unit. In instances where the air stream contains corrosive gases, the materials used to form the treatment unit are chosen to be as non-reactive as practical. Issues include treatment unit size, the need to deal with multiple contaminants that require different pH and moisture conditions for the support of the bio-organisms that remediate each of the contaminants and providing a control system that provides maximal remediation with minimal complexity.
Some of the most common air stream contaminants include hydrogen sulfide, mercaptans, amines and various organic acids. Hydrogen sulfide gas is toxic and very corrosive and is found in places as diverse as municipal sewage and sewer lines, oil well drilling locations, wood processing plants, and various other municipal and industrial processes in which elemental sulfur comes into contact with organic materials. This is the gas associated with the smell of ‘rotten eggs’. It is very toxic and can kill by asphyxiation, or by explosion.
A very effective method for treating hydrogen sulfide is to pass the air containing hydrogen sulfide through a highly porous, chemically inert media that is being bathed in water at a pH in the range of 1.8-2.2. Under these conditions a biological culture can be made to grow on the media and the cultured organisms will use hydrogen sulfide as a food source, converting the hydrogen sulfide to sulfuric acid using oxygen present in the air.
Organic Compounds other than hydrogen sulfide can be treated by moving the air containing these organic compounds through a highly porous, chemically inert media at a neutral or mildly alkaline pH while ensuring that the air is humidified and the media is kept moist through supplemental irrigation. Under these conditions a biological culture that will use these organic compounds as a food source can be made to grow on the media and convert those compounds to carbon dioxide and other by-products using oxygen present in the air.
Systems that try to simultaneously treat gas streams containing hydrogen sulfide as well as other organic compounds run into the following problem: oxidation of the hydrogen sulfide component of these complex air streams yields a by-product of sulfuric acid that interferes with the development of the biological substrate necessary for the treatment of the non hydrogen sulfide components of the air stream.
Oxidation of hydrogen sulfide takes place primarily at low pH conditions, and requires the use of autotrophic Thiobacillus bacteria. The bulk of the other contaminants commonly encountered in mixed contaminant airstreams require the use of heterotrophic bacteria at close to neutral pH conditions. The presence of both autotrophic and heterotrophic bacteria within a single treatment chamber causes a competition between the various bacteria at the required operating conditions. This in turn leads to reduced efficiency in the system because the non-separated fluid sections do not lend themselves to optimizing the pH in the sections of the treatment unit that are dealing with compounds requiring acid vs. neutral or base tolerant strains of microbial flora. It also leads to the need for using an increasingly complex system of trying to balance the pH of the water to the needs of the differing bacterial colonies within the treatment unit.
Bonnin et al., in U.S. Pat. No. 5,858,768, describe a system for the biodegradation of sulfurous compounds in combination with the physical/chemical elimination of organic nitrogenous compounds. The system is not continuous for the removal of both sets of pollutants, and though alteration of pH is provided for, the pH parameters described do not provide optimal target pH levels for either the acid or the base environment dependent microorganisms, thus likely leading to less efficiency in clearing Hydrogen sulfide gas. Like Horn, U.S. Pat. No. 5,869,323, Koers in U.S. Pat. No. 5,445,660 describes a system in which the polluted air is passed through at least two or more separate housings for purposes of treating pollutants requiring environments of differing pH and moisture for the biologically active components in the chambers. Needing multiple housings increases the cost and the number of connecting elements, pumps, seals and monitoring devices needed and thus would seem to create a less cost effective approach. Parker, et al in U.S. Pat. No. 7,276,366 describe a vertical treatment unit having two media containment sections within a unitary housing. However, the vertically stacked media sections are separated only by the perforated floor of the upper section. Contaminated air enters through an inlet at the bottom of the unit and passes sequentially upwards through both media bed sections and thence out an exhaust stack. Water for moistening the media bed, carrying in microorganisms or altering the pH can be introduced atop either the top section or the lower section in a reverse flow direction to the movement of air in the unit. However, any fluid entering the top section must percolate into and through the lower bed in order to enter the sump and exit the system, this raises the pH in the lower section. A complex, computer controlled system is required to periodically, and for a predetermined run time, alternate between passing fresh irrigating water, or recycling acidifying water from the sump into one or the other or both bed sections in an attempt to maintain pH in the 1.8-2.2 range for optimal clearance of Hydrogen sulfide in the lower (“Bioscrubber”) section. The upper (“Biofilter”) section pH being controlled in a similar manner such that it suits more alkaline loving microorganisms. Having a fluid connection between the bioscrubber and biofilter sections of the treatment unit leads to increased complexity of the control system and decreased specificity of the pH levels for optimal colonization of the microorganisms in the two sections of the treatment unit. As with any such media bed system, the vertical height is limited by the need to prevent compaction of and channel formation within the media beds. A series of these vertical units would be needed to handle larger volumes of contaminated air, resulting in the need for additional computer control systems which of course leads to a higher cost for the system.
Past designs for systems capable of remediating air streams containing mixed pollutants have suffered from the need to use multiple units for large scale operations and that led to increased installation costs. The fluid connection between the sections of the treatment units created alterations of pH that reduced the units' decontamination cost-efficiency. Some have required complex control systems to try and maintain proper pH, moisture levels and microbial populations tolerant of the pHs of the varying pollutants in the air stream because of the fluid communication between the internal sections of the unit.
Accordingly, it is an objective of this invention to provide a unitary housing treatment Unit having no fluid connection between its two or more, separated, fluid containing, internal treatment chambers.
A further objective is to provide a unitary, corrosion resistant, housing that can be created having the structural strength allowing for its use in large commercial and municipal reactors, yet also having a flexibility of design allowing for use in small sized reactors.
Another objective is to provide a treatment unit that allows optimal control of pH, moisture levels and microbial population purity within the separated internal sections of the structure that are intended to separately and sequentially remediate Hydrogen sulfide, which requires microorganisms that are very acid tolerant, and other pollutants such as mercaptans, amines and various organic acids that are dealt with by microorganisms that can only flourish at neutral or basic pH levels.
Another objective is to provide a system that is easily managed and largely self-regulating thus reducing operating costs.
The invention involves the creation of a unitarily housed air treatment system for the remediation of mixed air stream pollutants that embodies at least two separate treatment chamber sections, at least one of which requires the presence of microorganisms tolerant of a highly acidic pH while another or other sections require a neutral or basic pH. The design allows complete independent control of media bed pH, moisture levels, and microorganism population types within the two treatment chamber sections. The air pathway is from below upwards with countercurrent moisture application from above down in both treatment chambers. The only connection between the first and the following section(s) is an air-communication only channel which allows air that has passed through the more acidic treatment chamber wherein Hydrogen sulfide and like products are reduced, to move into the Unit's further chamber(s) without altering the moisture and pH thereof. Sensors and regulators are used to keep pH, moisture levels and rate of flow within predetermined parameters in both treatment chambers.
Further objectives advantages and novel features of the invention will be apparent to those skilled in the art from the following detailed description when taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention.
As seen in
Gas Channel 40 creates a non-fluid connection between Scrubber and Filter sections 100 and 200; the totality of the treatment Unit 1 externally comprising a front wall 110, a Scrubber section 100 roof 109; a dome shaped Filter section 200 roof 201, a rear wall 202 and a floor 203; the whole being fabricated of FRP, or of FRP reinforced by steel support members (none depicted) that are sealed away from the internal chambers of said Unit by being coated with a chemical resistant material when issues of size and weight dictate such reinforcement. Note: a pair of side walls 42
Continuing with the view shown in
The gas stream, now cleansed of some contaminants moves up and over the Scrubber section 100 rear wall 111, which will be noted extends below to the floor 203 and ends above at a short distance beneath the Scrubber section 100 roof 109, forming the front wall of the Gas Channel 40; a front wall 204 of the Filter section 200 forms the rear wall of Gas Channel 40; the Filter section 200 front wall 204 depends down from the Filter section 200 domed roof 201 and ends below at a perforated floor plate 205.
Perforated floor plate 205 serves as both the base of the Filter section 200 media bed 206 and as the top plate of the Filter section 200 sump section 217; the Filter section 200 sump 217 is drained by overflow drain 216 that allows water collected therein to be evacuated such that the sump 217 contains a headspace which serves as an entry plenum into which the gas stream being treated passes from Gas Passage 40.
Following which the gas stream moves up through perforated floor plate 205 into the Filter section 200 media bed section 206, then up into a moisturization chamber section 207 where supply water is added by a series of sprinklers 208 attached to a water inlet line array 209
The Filter section 200 perforated internal top plate 212 also serves as the floor of a gas stream exit plenum 213 where the purified gas collects and then moves up into a set of exhaust stacks 214 and finally into the ambient air mass.
Scrubber section 100 media bed section 103 contains an inert media 104 (cross hatching), such as conventional foam, reticulated foam, plastic or other such acid resistant synthetic materials; whichever media material is selected for use, that material is inoculated with and serves as the support substrate for colonies of autotrophic micro-organisms that feed on Hydrogen sulfide gas, the primary component of the gas stream removed in Scrubber section 100; less quantitavely prominent organic sulfides, ammonia, amines and such compounds are also removed in the scrubber 100 media bed 103.
Filter section 200 media bed section 206 contains an inert medium 215 (cross hatched area) such as granulated carbon, other carbon based media, wood chips, engineered media, lava rock or other such media that are inert to mildly alkaline solutions; whatever the media type selected for use, the media material is inoculated with and serves as the support for heterotrophic microorganisms that thrive in a neutral to mildly alkaline environment. These heterotrophic organisms digest organic nitrogenous compounds and other residual contaminants, thus removing them from the gas stream.
Note, the use of the terms “Scrubber” and “Filter” in the preceding and following text refers to two sections of the treatment Unit 1 that are designed to operate on differing component compounds of a multiply contaminated gas stream. Both use microorganisms colonized on base media for purposes of gas stream remediation. Neither section relies on a physical “filtration” system of purification. In all instances, the term “Scrubber” refers to the first air treatment chamber, which is kept at a low pH range, optimally pH 1.8 to 2.2, whereas the term “Filter” refers to the second air treatment chamber which is kept at a neutral to mildly alkaline pH range.
The microorganisms 104 and 215 respectively in the Scrubber and Filter 100 and 200 media bed sections 103 and 206 require a moist environment; moisturization is provided by sprinkler sets 105 and 208, the flow of water from which creates a counterflow movement of water down though the media beds 103 and 206; initially, the water entering both the moisturization chambers 107 and 207 is fresh inlet water from an outside source (not shown); that water having first been conformed to a specific pH range by a control system (not shown) that will be described later and presented diagrammatically in
pH regulated water from an external source continues to be the only moisturizing water used in Filter section 200 as long as the treatment Unit 1 is in operation. However, the digestion of hydrogen sulfide gas in the Scrubber section 100 leads to the formation of Sulfuric acid that mixes with and increases the acidity of the water to an undesirable pH as it passes down though the Scrubber section 100 media bed 103; this problem is corrected as follows: the hyper acidulated water passes down through air plenum 102 and then through perforated plate 113 into sump 114; some of the hyper acidulated water passes out of the system through a scrubber overflow drain 116; fresh water from an external source (not shown) is mixed in with the remaining hyper acidulated water in Scrubber section 100 sump 114 in order to bring the water into the proper pH range of 1.8 to 2.2, following which pH modification, the water is re-used in the Scrubber section 100 moisturization chamber 107.
No water is recirculated through the Filter section 200 media bed 206 which requires a neutral to alkaline pH and the water flowing into sump 217 passes through overflow drain 216 and is disposed of via the external drain system (not shown).
A Scrubber section 100 drain 117 (best seen in
When viewed from above as in
Thus, in
A contaminated gas stream enters from a source 41 and after passing from a contaminated gas stream inlet duct (not shown) that is attached to a flange 50, the gas passes through air inlet 101 and thus through the Scrubber section 100 as described prior. Gas Passage 40 is visible between the Scrubber section 100 rear wall 111 and the Filter section 200 front wall 204.
The topmost layer of the moisturizing support and delivery arrangement comprises: two cross braces 108 in the Scrubber section 100, and six cross braces 211 in the Filter section 200. In Filter section 200, longitudinal support beams 210 are affixed beneath the six cross braces 211 and the water line 209, comprising a central pipe with eight laterals, each of which terminates in a sprinkler 208 at both ends, is suspended beneath the longitudinal support beams 210 at each lateral offshoot of the sprinkler line 209.
The moisturizing support and delivery arrangement in the scrubber section 100 differs in that no longitudinal support beams are needed because of its short depth. The Scrubber section 100 water pipe 106 with its sprinklers 105 is suspended solely from the paired cross braces 108 to which it is attached.
For purposes of further orientation in
Gas Channel 40, as shown in greater detail in
Gas Channel 40 is formed anteriorly by the Scrubber 100 back wall 111 that is integrally attached to the floor 203 and ends above at a distance short of the roof 109; back wall 111 is integrally attached laterally to the right and left side walls 42 and 43 of Unit 1.
Contaminated gas enters the Scrubber section 100, and after passing through media section 103 and into moisturization chamber 107 as partially treated gas, the gas stream then follows the pathway shown by the arrow 44 and passes over the Scrubber back wall 111 and then downwards through Gas Channel 40.
The media bed 103 of Scrubber 100 terminates short of the top of the Scrubber section 100 back wall 107, and in conjunction with the Scrubber 100 overflow drain 116 that prevents excess buildup of exiting water, helps to insure that no water flows from the Scrubber section 100 into the Gas Channel 40 despite the constant counterflow of water entering the Scrubber 100.
Filter section 200 front wall 204 forms the back wall of Gas Channel 40 and is integrally attached above to the Filter section 200 roof 201 and side walls 42 and 43, ending below a short distance from floor 203; thus presenting a space through which the on-moving gas stream, following the direction indicated by arrow 45, turns into the Filter section 200 combination fluid sump/gas stream entry plenum 217; the gas stream then moves upwards through the Filter section 200 media bed 206, etc. as described prior.
As described prior, overflow drain 216 removes excess water from the Filter section 200 sump 217 and sends it into a waste water drain, thus preventing a backup of the treatment water from the Filter section 200 into the Gas Channel 40.
A control panel (“Panel”) 47
Continuing with the view presented in
Water from an external source (not shown) enters via a water inlet valve 308 and thus into a fresh water line 309 where it passes through a pressure regulator 310 then a pressure gauge 311; at this point the water line 309 splits into two separate supplies, one line, a Filter section 200 inlet water line 312, which always delivers only fresh water, passes through a solenoid valve and its associated electrical control wire 314 that is activated by the timer 306 located in control panel 47; timer 306 is set to intermittently spray into the Filter section 200 moisturization chamber 207 using the Filter section 200 sprinkler sets 208 described prior; a port and valve 48 arrangement is located on inlet water line 312 for adding inoculation material, nutrients and other such agents to the Filter section's 200 media bed 206.
The second branch off from fresh water line 309 is a make up water line 313 which first passes through a rotameter 315; the rotameter 315 is adjusted after use and trial to provide a pre-set, stable rate of flow of water to the Scrubber sump 114 from whence the water is then drawn into a recirculation system water line 316 by a recirculation pump 317 which is activated when pump power switch 304 is set in the on position and the signal from pump power switch 304 is carried to the recirculation pump 317 via an electric power line 323; after passing through the recirculation pump 317, the water passes by a pressure gauge 318 then past a pH probe 319 that sends a signal via an electrical control wire 320 to the pH meter 305 in control panel 47; continuing past the pH probe 319, the water passes through a flow transmitter 321 the signal from which passes via an electrical control wire 322 sequentially into indicator light 302, flow relay 303 and thus to pump power switch 304. Flow transmitter 321 serves as a fail safe device and should the water level in the system fall below a critical level, the flow transmitter's 321 altered signal intensity reaches the flow relay 303, which in turn will trip the pump power switch 304, thus turning off the recirculation pump 317 and preventing damage to same; having passed by flow transmitter 321, the water next passes a port and valve 49 located on recirculation line 316; port and valve 49 serve to allow addition of inoculant material, nutrients and other such agents to the scrubber's 100 media bed 103 as needed; finally, the pH corrected water is delivered to the Scrubber section's 100 internal sprinklers 105, the placement of which was described prior.
Because the Scrubber section 100 uses water from the Scrubber sump 114 mixed with some fresh water to maintain an optimal pH in the Scrubber section 100 media bed 103, provision is made for some excess water to escape via an overflow drain system comprising an overflow drain 116 and an overflow drain line 325. Overflow drain line 325 has a trap 326 for the prevention of back flow into the Scrubber section 100 sump 114.
Both Scrubber section 100 and Filter section 200 sumps 114 and 217 have access to a main drain line 327
Note: although they are not part of the control system, exhaust stacks 214 (represented by arrows indicating the final direction of the gas stream flow) are shown for purposes of orientation.
A differential pressure gauge array 330, for the Scrubber section 100, which serves to register the pressure differential at the inlet and exit peripheries of the media bed 103, comprises an externally visible differential pressure gauge attached to a pair of pressure sensitive probes 51 and 52, one of which probes 51 is situated in Scrubber 100 air entry plenum 102 and the other of which probes 52 is situated in the moisturization chamber 107, thus bracketing the media chamber 103 of the Scrubber 100 and allowing determination of and serving warning of bed-compaction or other such problems if the inlet and exit pressure differential becomes too great.
A differential pressure gauge array 331, for the Filter section 200, which serves to register the pressure differential at the inlet and exit peripheries of the media bed 206 comprises an externally visible differential pressure gauge having a pair of pressure sensitive probes 53 and 54, one of which probes 53 is situated in Filter 200 air entry plenum 217 and the other of which probes 54 is situated in moisturization chamber 207, thus bracketing the media chamber 206 of the Filter 200 and allowing determination of and serving warning of bed-compaction or other such problems if the inlet and exit pressure differential becomes too great.
