WO2009132424A1 - Système de barboteur pour le lavage du biogaz - Google Patents

Système de barboteur pour le lavage du biogaz Download PDF

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Publication number
WO2009132424A1
WO2009132424A1 PCT/CA2009/000537 CA2009000537W WO2009132424A1 WO 2009132424 A1 WO2009132424 A1 WO 2009132424A1 CA 2009000537 W CA2009000537 W CA 2009000537W WO 2009132424 A1 WO2009132424 A1 WO 2009132424A1
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Prior art keywords
gas
tank
solution
tanks
scrubbing
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PCT/CA2009/000537
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English (en)
Inventor
Richard Allen
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Richard Allen
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Publication of WO2009132424A1 publication Critical patent/WO2009132424A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
    • B01D53/1406—Multiple stage absorption
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
    • B01D53/1456—Removing acid components
    • B01D53/1462—Removing mixtures of hydrogen sulfide and carbon dioxide
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
    • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
    • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
    • C10L3/08—Production of synthetic natural gas
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
    • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
    • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
    • C10L3/10—Working-up natural gas or synthetic natural gas
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
    • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
    • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
    • C10L3/10—Working-up natural gas or synthetic natural gas
    • C10L3/101—Removal of contaminants
    • C10L3/102—Removal of contaminants of acid contaminants
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
    • C12M47/00—Means for after-treatment of the produced biomass or of the fermentation or metabolic products, e.g. storage of biomass
    • C12M47/18—Gas cleaning, e.g. scrubbers; Separation of different gases
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/05—Biogas
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/40—Capture or disposal of greenhouse gases of CO2
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/59—Biological synthesis; Biological purification

Definitions

  • the invention relates to the production of commercial-grade natural gas. More particularly, this invention relates to the scrubbing of biogas produced by anaerobic fermentation to produce commercial-grade natural gas.
  • Anaerobic digestion systems are commonly employed for municipal, industrial and agricultural conversion of organic wastes into biogases that are commonly captured for use in heat and/or electrical power generation.
  • Anaerobic conversion of organic wastes into biogases generally occurs along a four-stage process comprising (a) a first stage during which complex organic molecules are hydrolyzed into soluble monomers such as monosaccharides, amino acids and fatty acids (i.e., hydrolysis), followed by (b) a second stage during which the simple monomers produced during the first stage, are converted into volatile fatty acids (i.e., acidogenesis), then (c) a third stage during which the volatile fatty acids are converted into acetic acid, carbon dioxide, and hydrogen (i.e., acetogenesis), and finally (d) the fourth stage where the acetic acid is converted into methane, carbon dioxide, and water (methanogenesis).
  • Biogas produced by such anaerobic conversions comprises primarily methane, secondarily carbon dioxide, variable amounts of ammonia, and trace amounts of nitrogen gas, hydrogen, oxygen and hydrogen sulfide.
  • Such biogas products are commonly combusted on-site in suitable furnaces and/or engines for the production of heat, electricity, and/or motive power to supply or supplant the facilities' utilities requirements.
  • a gas cleaning apparatus including: a first tank for containing a methyldiethanolamine solution, the first tank having an inlet for receiving the gas, bubbler pipes coupled to the inlet for bubbling the gas through the methyldiethanolamine solution to remove hydrogen sulfide (H 2 S) from the gas and an outlet for outputting H 2 S scrubbed gas; and a second tank for containing a monoethanolamine solution, the second tank having a second inlet in communication with the outlet for receiving the H 2 S scrubbed gas, bubbler pipes coupled to the second inlet for bubbling the H 2 S scrubbed gas through the monoethanolamine solution to remove carbon dioxide (CO 2 ) from the H 2 S scrubbed gas and a second outlet for outputting H 2 S and CO 2 scrubbed gas; wherein the methyldiethanolamine solution and the monoethanolamine solution are continuously regenerated through heat application.
  • a process for sequentially scrubbing hydrogen sulphide gas (H 2 S) and carbon dioxide (CO 2 ) from a mixed gas stream including: bubbling the mixed gas stream under low pressure through at least one scrubber tank containing therein a volume of a methyldiethanolamine (MDEA) solution, thereby producing a H 2 S-scrubbed mixed gas stream; transferring the H 2 S- scrubbed mixed gas stream to at least one other scrubber tank containing therein a volume of monoethanolamine (MEA) solution and bubbling the H 2 S-scrubbed mixed gas stream through the MEA solution to produce a purified gas stream; and transferring the purified gas stream to a gas-storage tank.
  • MDEA methyldiethanolamine
  • a bubbler pipe assembly for a gas scrubbing tank containing an amine solution, the bubbler pipe assembly including: an inlet for receiving a gas; and bubbler pipes coupled to an inner wall of the gas scrubbing tank, the bubbler pipes being in communication with the inlet and each of the bubbler pipes having a plurality of holes for expelling the gas through the amine solution; wherein one of hydrogen sulfide (H 2 S) and carbon dioxide (CO 2 ) is removed from the gas as the gas is bubbled through the amine solution.
  • H 2 S hydrogen sulfide
  • CO 2 carbon dioxide
  • Figure 1 is a schematic flow diagram illustrating an experimental system used to bubble a gas containing an impurity sequentially through two bubbler scrubbing tanks according to an embodiment of the present invention
  • Figure 2 is a schematic close-up view of the bubbler scrubbing tank of Figure 1 ;
  • Figure 3 is a schematic flow diagram showing the experimental system from
  • Figure 1 additionally provided with a regeneration tank infrastructure interconnected to each of the two bubbler scrubbing tanks;
  • Figure 4 is a schematic close-up view of a regeneration tank for recharging the amine scrubbing solution from the bubbler scrubbing tank of Figure 2;
  • Figure 5 is a schematic view of an example of a commercial-scale system according to the present invention.
  • Figures 6 and 7 are schematic process flow diagrams of a gas cleaning apparatus according to an embodiment of the present invention.
  • Figure 8 is side view of a H 2 S removal tank of the gas cleaning apparatus of
  • Figure 9 is a top view of the H 2 S removal tank of Figure 8.
  • Figure 10 is an end view of the H 2 S removal tank of Figure 8.
  • Figure 11 is a side view of a bubbler pipe assembly of the H 2 S removal tank of
  • Figure 12 is a top view of a bubbler pipe assembly of the H 2 S removal tank of
  • Figure 13 is a side view of a rich amine tank and regeneration tank of the gas cleaning apparatus of Figures 6 and 7;
  • Figure 14 is a side view of a weir plate of the rich amine tank and regeneration tank of Figure 13;
  • Figure 15 is a view on 15-15 of Figure 13;
  • Figure 16 is a view on 16-16 of Figure 13;
  • Figure 17 is a front view of the rich amine tank and regeneration tank of Figure
  • Figure 18 is a back view of the rich amine tank and regeneration tank of Figure
  • Figure 19 is a top view of the rich amine tank and regeneration tank of Figure 13.
  • Figure 20 is a graph showing boiling points and condensation temperatures of monoethanolamine (MEA).
  • MEA monoethanolamine
  • Natural gas is known by consumers as a clean-burning fuel comprising primarily methane. Natural gas is delivered to industrial and residential consumers by continental networks of transmission pipelines leading back to natural gas processing facilities that are located close to the terrestrial or off-shore sources of natural gas deposits. These deposits include oil fields, natural gas fields, and coal deposits. Raw natural gas removed from these deposits contains in addition to methane, significant quantities of ethane, propane, butane and pentane, as well as carbon dioxide, nitrogen, helium and hydrogen sulfide. Consequently, raw natural gas must undergo extensive processing through a series of steps at facilities close to its terrestrial sources, to remove the various impurities so that the purified final product meets the quality standards specified by the major pipeline transmission and distribution companies.
  • the standards specify that the natural gas: (a) be within a specific range of heating value (caloric value), (b) b delivered at or above a specified hydrocarbon dew point temperature (below which some of the hydrocarbons in the gas might condense at pipeline pressure forming liquid slugs which could damage the pipeline), (c) be free of particulate solids and liquid water to prevent erosion, corrosion or other damage to the pipeline, (d) be dehydrated of water vapor sufficiently to prevent the formation of methane hydrates within the gas processing plant or subsequently within the sales gas transmission pipeline, (e) contain no more than trace amounts of components such as hydrogen sulfide, carbon dioxide, mercaptans, nitrogen, and water vapor, and (f) maintain mercury at less than detectable limits (approximately 0.001 parts-per-billion by volume) primarily to avoid damaging equipment in the gas processing plant or the pipeline transmission system from mercury amalgamation and embrittlement of aluminum and other metals.
  • the embodiments of the present invention are directed to apparatus' and methods for processing biogas produced by anaerobic digestion systems, thereby producing primarily a "natural gas" quality product that meets the quality specification standards set by pipeline transmission and distribution companies.
  • One embodiment of the present invention includes a low-pressure two-step method for processing "raw" biogas produced by anaerobic digestion systems.
  • the first step generally comprises removal i.e., scrubbing of H 2 S from a biogas stream by bubbling the biogas at a pressure of about 1 to 2 psi through a tank containing a 90%- pure (or purer) methyldiethanolamine (MDEA) solution.
  • MDEA 90%- pure (or purer) methyldiethanolamine
  • the second step generally includes removal of carbon dioxide (CO 2 ) from the H 2 S-scrubbed biogas by bubbling the scrubbed biogas through a tank containing a 90%-pure (or purer) monoethanolamine (MEA) solution.
  • the CO 2 -scrubbed biogas which is also referred to as "purified anaerobic natural gas", collects in the headspace at the top of the MEA tank and is transferred by piping to a natural gas storage tank.
  • the first step may additionally include bubbling the raw biogas through a tank containing water to remove ammonia and dirt particles and may be performed before or after bubbling the biogas through the MDEA solution for removal of H 2 S.
  • the second step may additionally include, after bubbling the scrubbed biogas through the MEA solution, a "finishing" step wherein the processed anaerobic biogas is bubbled through a tank containing glycol to remove water from the final biogas product to ensure that it meets the quality standards for natural gas as specified by the major pipeline transmission and distribution companies.
  • Another embodiment includes an apparatus for processing "raw" biogas produced by anaerobic digestion systems with the low-pressure two-step processing method of the present invention.
  • the apparatus generally includes a series of horizontally orientated elongate bubbler tanks, each configured for executing one of the steps of the present invention.
  • Each tank is provided with gas-inflow piping that extends along the length of the tank, one end of said gas-inflow piping controllably communicable with an external supply of a biogas.
  • the gas-inflow piping is provided with plurality of holes drilled therethrough along the length of the piping.
  • Each tank is also provided with a gas outlet piping sealingly fixed into the top of the tank.
  • the gas outlet piping sealingly fixed into the top of the tank containing the MDEA solution, is sealably interconnected with the gas-inflow piping provided within the tank containing the MEA solution.
  • the gas-inflow piping provided within each tank is fixed horizontally in the tank such that the piping is submerged within the amine solution added to the tank.
  • the gas-outlet piping sealingly fixed into the top of the tank containing the MEA solution, is sealingly interconnected with a natural gas storage tank.
  • Each tank is additionally provided with solution-recycling piping infrastructure interconnected with a system configured for recharging the solution contained within the tank.
  • the recharging system maybe a boiling tank for boiling off the H 2 S from the MDEA solution, or alternatively for boiling off CO 2 from the MEA solution whereby the boiled amine solutions are recharged and then returned to their respective scrubbing tanks.
  • the recharging system may be a heat-exchange unit wherein the amine solutions are controllably heated for separation of the scrubbed gases therefrom after which, the recharged amine solutions are returned to the scrubbing tanks.
  • the H 2 S gas separated from the MDEA solution during the recharging process is collected and then burned, while the CO 2 separated from the MEA solution during the recharging process is vented into the atmosphere.
  • the separated CO 2 may be collected and stored in tanks for venting into greenhouse environments, or alternatively, liquified for other industrial applications.
  • FIG. 1 An experimental system was configured as shown in Figure 1 to assess the feasibility of bubbling under low pressure, a gas containing a selected impurity through a selected amine scrubbing solution.
  • the experimental system consisted of a pre-mixed and pressurized gas supply 10, an in-line series of valves, pressure meters and gas- flow controllers 12 in a gasline provided between the pressurized gas supply and a first bubbler scrubbing tank 14.
  • a length of sparging pipeline 11 was provided just above the bottom of the scrubbing tank that was sealably extended therethrough the side of the scrubbing tank, and was sealably interconnected to the gas-supply line (Figure 2).
  • An outlet gas pipe was sealably extended through the top of the first scrubbing tank 14 and was sealably interconnected to the inlet of a sparging pipeline extending from the side of a second bubbler scrubbing tank 16 outfitted and configured similarly to the first bubbler scrubbing tank 14.
  • the outlet gas pipe 18 extending therefrom the top of the second scrubbing tank was vented to the atmosphere ( Figure 1).
  • the outlet gas pipe 18 extending from the top of the second scrubbing tank would be interconnected with a purified gas storage tank.
  • a gas- sampling port was installed into the piping infrastructure interconnected with the outlet gas pipe extending from the second scrubbing tank 16.
  • the gas-sampling port was interconnected with piping infrastructures configured for delivering gas samples to gas analytical equipment exemplified by gas chromatographs 20 and rotameters 22, and for venting sampled gases through outlet gas pipe 24.
  • the gas-sampling piping infrastructure was provided with suitable inline check-valves, pressure monitoring instruments and mass-flow controllers.
  • the two bubbler scrubbing tanks 14, 16 were filled about 3 A full with MEA (the first scrubbing tank received 15.8 kg of 90%+ pure MEA; the second scrubbing tank received 10.9 kg of 90%+ pure MEA).
  • the gaslines were purged with nitrogen gas (N 2 ) for 10 min.
  • the test gas was fed into the experimental system with a flow rate of about 12 to 24 standard liters per minute (slpm).
  • the flow of test gas through the two scrubbing tanks was maintained for 4.5 hrs.
  • the following parameters were measured at regular intervals during the 4.5-hr test period: weight of each scrubbing tank, temperature of the MEA solution in each scrubbing tank, flow rate of test gas into the first scrubbing tank, gas pressure at the outlet-gas sampling port from each scrubbing tank, and the % CO 2 and % CH 4 sampled from the gas-sampling port at each sampling period.
  • Table 1 The data pertaining to changes in the weights, temperatures and gas pressures developed in each scrubbing tank over the 4.5 hr test period are shown in Table 1.
  • the changes in the composition of purified test gas during the test period are shown in Table 1.
  • Table 1 Changes in weight, temperature, and gas pressure in each scrubbing tank.
  • Table 2 Gas content of the purified gas exiting the second scrubbing tank.
  • the data in Table 1 indicate that the weight of the first scrubbing tank increased slightly during the 4.5 hr test period (i.e., from 10.9 kg to 11.2 kg). A larger increase was observed in the second scrubbing tank (i.e., from 10.9 kg to 11.2 kg) indicating a larger amount of CO 2 was being sequestered therein. Similarly, a larger increase in the temperature of the MEA solution was observed in the second scrubbing tank (i.e., from 18.2° C to 110.3° C) than in the first scrubbing tank (i.e., from 18.0° C to 30.6° C). The rate of test gas flow into this experimental system, was increased from 12 slpm to ⁇ 24 slpm after 3 hours. It was noted that the gas pressures created at the gas outlet of each tank were comparable at both test gas inflow rates.
  • Example 1 The experimental system described in Example 1 was used to assess the removal of H 2 S and CO 2 gases from a test gas comprising 1.2% H 2 S, ⁇ 50.4% CO 2 , and about - 48.4% C 4 H.
  • the two scrubbing tanks were filled about 3 A full with MDEA though liquid inlet 28. Outlet 30 is provided for draining of liquid from the scrubbing tanks to a recharger.
  • the two bubbler scrubbing tanks were filled about 3 A full with MDEA (the first scrubbing tank received 16.4 kg of 90%+ pure MDEA; the second scrubbing tank received 11.0 kg of 90%+ pure MDEA).
  • the gaslines were purged with nitrogen gas (N 2 ) for 10 min.
  • the H 2 S:CO 2 :C 4 H test gas was fed through gas inlet 24 into the experimental system with a flow rate of about 6 to 8 slpm.
  • the flow of test gas through the two scrubbing tanks was maintained for about 3 hrs.
  • the following parameters were measured at regular intervals during the 3-hr test period: weight of each scrubbing tank, temperature of the MDEA solution in each scrubbing tank, flow rate of test gas into the first scrubbing tank, gas pressure at the outlet-gas sampling port 32 from each scrubbing tank, and the % H 2 S, % CO 2 , and % CH 4 sampled from the gas-sampling port at each sampling period.
  • Table 3 Changes in weight, temperature, and gas pressure in each scrubbing tank.
  • Table 4 Gas content of the purified gas exiting the second scrubbing tank.
  • Example 1 The experimental system described in Example 1 was fitted with an amine- recharging system (Figure 3) interconnected to the two bubbler scrubbing tanks shown in Figure 1.
  • the amine-recharging system comprised a recharger tank 36 ( Figure 4) having an immersion heater 42 and a piping infrastructure interconnecting the recharger tank inlet 38 and tank outlet 40 with the two bubbler scrubbing tanks.
  • the two bubbler scrubbing tanks were filled about 3 A full with MEA (the first scrubbing tank received 23.4 kg of 90%+ pure MEA; the second scrubbing tank received 15.2 kg of 90%+ pure MEA).
  • the gaslines were purged with nitrogen gas (N 2 ) for 10 min.
  • the test gas was fed into the experimental system with a flow rate of about 18.6 slpm.
  • the flow of test gas through the two scrubbing tanks was maintained for 2% hrs.
  • Table 5 Changes in weight, temperature, and gas pressure in each scrubbing tank.
  • Table 6 Gas content of the purified gas exiting the second scrubbing tank.
  • FIG. 5 An example of a commercial-scale apparatus of the present invention is shown in Figure 5 and generally includes: (a) at least one bubbler scrubbing tank 46, 48 containing therein a high-purity MDEA solution for bubbling a "raw" methane-containing gas mixture therethrough, (b) at least one bubbler scrubbing tank 50, 52 containing a high-purity MEA solution for receiving a partially-scrubbed methane-containing gas mixture from the MDEA-containing tank, and bubbling said gas therethrough to provide a "natural gas" product that satisfies the specifications set by natural gas the quality standards specified by the major pipeline transmission and distribution companies.
  • the MDEA-containing bubbler scrubbing tank is interconnected to an inlet 54 receiving a supply of a methane-containing gas mixture with the gas-supply line provided with an inline series of valves, pressure meters and gas-flow controllers to controllably deliver the gas mixture to the bubbler tank under a very low pressure, e.g., less than 50 psig. It is within the scope of the present invention to provide two or more interconnected MDEA- containing bubbler scrubbing tanks for scrubbing H 2 S from the incoming gas mixture.
  • the partially-scrubbed gas mixture sparged from the first MDEA-containing tank is conveyed via a piping infrastructure to the sparging pipeline submerged in the second MDEA-containing tank for bubbling therethrough the MDEA solution thereby removing more or alternatively, all of the remaining H 2 S from the gas mixture.
  • the two or more MDEA-containing tanks are interconnected with a MDEA-recharging system including a piping infrastructure configured for delivering gas-laden MDEA solution to a recharger apparatus 56 and a piping infrastructure configured for returning the re-charged MDEA solution to the two or more MDEA-containing tanks.
  • the H 2 S-scrubbed gas mixture emanating from the last MDEA-containing bubbler scrubbing tank is interconnected via a gasline provided with an in-line series of valves, pressure meters and gas-flow controllers, to the MEA-containing tank for removal therein of CO 2 gas therefrom the gas mixture. It is within the scope of the present invention to provide two or more interconnected MEA-containing bubbler scrubbing tanks for scrubbing CO 2 from the gas mixture.
  • the partially-scrubbed gas mixture sparged from the first MEA-containing tank is conveyed via a piping infrastructure to the bubbler pipeline submerged in the second MEA-containing tank for bubbling therethrough the MEA solution thereby removing more or alternatively, all of the remaining CO 2 from the gas mixture.
  • the two MEA-containing tanks are interconnected with a MEA-recharging system comprising a piping infrastructure configured for delivering gas-laden MEA solution to a recharger apparatus 58 and a piping infrastructure configured for returning the re-charged MEA solution to the two MEA-containing tanks.
  • the natural gas product emanating from the last MEA-containing tank is transferred via a suitably configured gas line system to a natural gas storage tank 60.
  • the stored natural gas is transferable into a natural gas transmission pipeline by supply pipeline infrastructure wherein is interposed a suitable gas-pressurizing pump.
  • the stored natural gas may be transferred to any suitable storage tank communicating with a combustion system configured to combust natural gas for producing heat, utilities, and/or motive power.
  • a gas cleaning apparatus 10 for processing "raw" biogas produced by anaerobic digestion receives biogas from a digester 70 and includes a foam suppression tank 112, first and second H 2 S removal (scrubbing) tanks 114 and 116, respectively, a H 2 S scavenger tank 118, first and second CO 2 removal tanks 120 and 122, respectively, a lean amine tank 124, a rich amine tank 125 and an amine regenerator tank 126.
  • a gas storage tank (not shown) is further provided to capture and store clean gas produced by the gas cleaning apparatus 10.
  • Operation of the apparatus 10 generally includes removal of foam, ammonia and dirt particles from the biogas at the foam suppression tank 112 followed by removal of H 2 S by one of the H 2 S removal tanks 114, 116, removal of more H 2 S by the H 2 S scavenger tank 118, removal of CO 2 by the first and second H 2 S removal tanks 120, 122 and, finally, compression of clean gas for storage in the gas storage tank.
  • the biogas exits the digester 70 under a pressure of less than 1 psi. This low pressure is generally maintained as the gas travels through the gas cleaning apparatus 10.
  • a gas line 140 connects the foam suppression tank 112 to a digester.
  • the gas line 140 includes a slope for directing condensation into the foam suppression tank 112.
  • Nozzles 130 are provided for spraying chilled water onto the biogas as it enters the foam suppression tank 112.
  • the nozzles 130 receive water from a water source 132 through a supply line 134, which passes through a chiller 136 to cool the water. Chilled water may alternatively be obtained directly from the water source 132.
  • Biogas is directed through the foam suppression tank 112 by partition 138. As the biogas cools to a lower dewpoint, foam, dirt, ammonia and most of the water is removed.
  • Siloxanes are generally not present in agricultural digesters, however, in non- agricultural applications, the cold spray removes a percentage of siloxanes.
  • An automatic float shut off 146 is located at the exit to the foam suppression tank 112.
  • the automatic float shut off 146 blocks the tank exit to avoid contamination of the H 2 S removal tank 14 in the case where foam or liquid overwhelms the foam suppression tank 112.
  • the pressure in the foam suppression tank 112 increases and the biogas is diverted to the flare line 144.
  • the flare line 144 communicates with a flare stack 145 that burns the H 2 S and vents to the atmosphere.
  • a pressure relief valve 142 is provided to allow gas to flow into the flare line 144.
  • a separate storage tank (not shown) is provided to receive water that builds up in the foam suppression tank 112. Some of the water is re-chilled and pumped back to the nozzles 130 and the remainder of the water is treated, if necessary, with a tri-azine based liquid scavenger for trace H 2 S absorption and pumped into a temporary storage area for re-use. A percentage of fresh water is added at the nozzles 130 to ensure that the water doesn't become saturated with ammonia, ensuring that all of the ammonia is absorbed in this step.
  • the foam suppression tank 112 directs cooled, partially cleaned gas through gas line 148 to the H 2 S removal tank 114, 116.
  • the first and second H 2 S removal tanks 114, 116 are provided in parallel and are generally identical. Each of the tanks 114, 116 is partially filled with an aqueous solution of methyldiethanolamine (MDEA) and water.
  • MDEA methyldiethanolamine
  • One H 2 S removal tank 114, 116 is in use while the other H 2 S removal tank 114, 116 is on standby. While on standby, the MDEA in the H 2 S removal tank 114, 116 is regenerated.
  • the optimal solution strength of MDEA and water is determined through experimentation. In one embodiment, the solution strength is 50% or purer.
  • the H 2 S removal tank 114 includes a tank body 150 having an inner wall 152 that defines a cavity 154 for receiving the MDEA solution.
  • MDEA solution enters the tank through amine inlet 155.
  • a level of the MDEA solution in the tank 114 is indicated by reference numeral 156.
  • a bubbler pipe assembly 158 is submerged in the MDEA solution and is supported by bars 160 that are coupled to the inner wall 152 of the tank 114.
  • the bubbler pipe assembly 158 includes an inlet 162 and a plurality of bubbler pipes 164 having holes 166 provided along the length thereof.
  • the bubbler pipe assembly 158 receives cooled, partially cleaned gas from the foam suppression tank 112 and bubbles the gas through the MDEA solution to remove H 2 S is therefrom while leaving the CO 2 in the gas stream.
  • H 2 S-scrubbed gas passes through a condenser 170 and exits the tank 114 through outlet 172.
  • the tank 114 and bubbler pipe assembly 158 are made of stainless steel, however, another corrosion-resistant material may alternatively be used.
  • a heating coil 166 and a cooling coil 168 are provided in the H 2 S removal tank 14 for use in regeneration of the MDEA. Regeneration is performed by applying heat from the heating coil 166. Temperature control during absorption and cooling following regeneration is facilitated by the cooling coil 168.
  • a monitoring device (not shown) is provided to continuously monitor the H 2 S level in the gas exiting the H 2 S removal tank 114. When a maximum H 2 S level in the gas exiting the tank 114 is reached, the gas cleaning process is temporarily halted and the MDEA in the tank 114 is regenerated. The regeneration process involves flaring off H 2 S from the saturated MDEA in the H 2 S removal tank 114.
  • Flare lines 174, 176 are provided to deliver the resulting acid gas stream from MDEA regeneration to the flare stack 145 for combustion.
  • the gas travels through gas line 178 to the H 2 S scavenger tank 118 where the gas is polished to pipeline specifications.
  • the H 2 S scavenger tank is typically purchased from a third party. Manufacturers including Sulfa Treat, Sulfa Bind and Canwell Enviro industries, for example, produce scavenger tanks suitable for use in the gas cleaning apparatus 10.
  • the H 2 S removal tank 114, 116 removes the majority of the H 2 S before the gas arrives at the H 2 S scavenger tank 16.
  • the H 2 S scavenger tank 118 then reduces the H 2 S content in the gas to the level required. While the H 2 S scavenger tank 118 is capable of effectively removing H 2 S concentrations as high as 50%, they are less cost effective for H 2 S concentrations above 300 to 500 ppm because the H 2 S scavenger tank 118 cannot be regenerated.
  • the removal of H 2 S from the H 2 S removal tank 114, 116 via the regeneration process greatly increases the life of the H 2 S scavenger tank 118.
  • Spent scavenger material is non-hazardous and is suitable for disposal in a Class Il landfill.
  • H 2 S-scrubbed gas having a H 2 S concentration that has been polished to pipeline specifications exits the H 2 S scavenger tank 118 and travels through a gas line 180 to a first CO 2 removal tank 120.
  • the first CO 2 removal tank 120 and a second CO 2 removal tank 122 are provided in series and connected by a gas line 182.
  • Each tank 120, 122 is partially filled with a solution of anhydrous monoethanolamine (MEA).
  • MEA anhydrous monoethanolamine
  • each CO 2 removal tank 120, 122 includes a bubbler pipe assembly 158 that is submerged in the MEA solution.
  • the bubbler pipe assembly 158 receives and bubbles H 2 S-scrubbed gas through the MEA solution, which removes CO 2 therefrom.
  • the tanks 120, 122 and bubbler pipe assembly 158 are made of stainless steel, however, another corrosion-resistant material may alternatively be used.
  • Clean gas exits the second CO 2 removal tank 122 and travels through a gas line 190 to a gas blower 192 and a compressor (not shown).
  • the clean gas exits the second CO 2 removal tank 122, it has been scrubbed to pipeline specifications for everything except water, which is removed when the clean gas is compressed for storage in the gas storage tank.
  • Clean gas is compressed by the blower 192 at about 5 to 10 psig, metered, and then fed into the gas line 190 going to the storage tank.
  • the gas line 190 may be heated so that the gas is above the ambient temperature of the ground.
  • the water dew point of the gas is generally below approximately 5 0 C when it exits the foam suppression tank 112 and some of the water is absorbed by the MDEA and MEA. At low operating pressure, gas hydrate formation is not generally encountered.
  • the first CO 2 removal tank 120 is mounted on load cells (not shown), which monitor the increase in weight as the MEA solution absorbs CO 2 and indicate when the MEA solution is saturated.
  • MEA solution that is saturated with CO 2 has a mass density about 18% greater than lean MEA solution.
  • the second CO 2 removal tank 122 contains lean amine, which is MEA solution that does not include absorbed CO 2 .
  • the second CO 2 removal tank 122 is provided to absorb any CO 2 that breaks through from the saturated first tank 120.
  • a circulation pump (not shown) in the lean amine tank 124 is activated and lean amine is pumped through supply line 184 into the second CO 2 removal tank 122.
  • the second CO 2 removal tank 122 is located at a higher elevation than the first CO 2 removal tank 120 so that the lean amine flows through the second CO 2 removal tank 122 and cascades down to the saturated first tank 120 via supply line 186.
  • the lean amine flows from the second CO 2 removal tank 122 into the first CO 2 removal tank 120, it displaces some of the heavier saturated MEA solution, which in turn, overflows into the rich amine tank 125 through rich amine inlet 128.
  • the circulation pump shuts off. The process repeats when the MEA of the first tank 120 becomes saturated with CO 2 again.
  • a rich amine outlet 204 of the rich amine tank 125 and an amine inlet 206 of the regeneration tank 126 are in fluid communication via a connecting pipe (not shown).
  • Rich amine which is MEA solution that is saturated with CO 2
  • the regeneration tank 126 includes a flat bottom 208 that is heated to a maximum of 15O 0 C by immersed heating coils 210.
  • the heating coils 210 receive heat medium solution from a heat exchanger 212 of the compressor station through an inlet 215.
  • the heat medium solution exits the heating coils 210 through an outlet 211.
  • the heat medium may be a mixture of water and triethylene glycol or another suitable heat medium.
  • the bottom 208 of the regeneration tank 126 is approximately 3' wide, 15' long and is sloped approximately 6" from end to end to allow the rich amine to flow gradually down the length of the tank heating up and releasing CO 2 as it goes.
  • a series of shallow, notched weir plates 214 spaced approximately 12 inches apart along the length of the bottom 208 of the tank are provided to ensure that the thick amine flows and distributes itself evenly and doesn't channel along the flat bottom of the regeneration tank 126.
  • the regeneration tank 126 is configured to allow as much surface area as possible to contact the amine while maintaining the amine depth as shallow as possible to reduce hydrostatic head and allow the CO 2 to escape quickly through the regenerator outlet 195.
  • Flow out of the rich amine tank 125 is controlled by a valve (not shown) that is manually adjustable to ensure the optimal flow rate is maintained.
  • the CO 2 that is boiled off passes through a vapour condenser 194 and though a gas line 218 to a vent stack 216 for release to the atmosphere.
  • the vapour condenser 194 condenses the majority of the amine that has been entrained with the CO 2 , so that it is recovered and runs back into the tank. Trace amounts of MEA are also boiled off with the CO 2 .
  • An MEA knock out tank 220 is provided to receive MEA that condenses in the gas line 218.
  • the lean amine flows through a liquid trap amine outlet 188, which is similar to a kitchen sink, so the CO 2 is forced out the top of the vent stack 216.
  • the hot, lean amine flows through a heat exchange coil (not shown) to be cooled and an activated carbon filter (not shown) to remove any absorbed hydrocarbons.
  • the lean amine then flows back into the lean amine tank 124, ready to be pumped back into the second tank 122 again.
  • the heating coils 210 of the regeneration tank 126 receives heat medium solution that is heated by heat exchanger 212, which is part of compressor station that is located nearby. In many applications, access to a large heat source is not available, therefore, heat is obtained from boilers 222 and 224. An expansion tank 226 is provided take up extra pressure from the heat medium as it exits the regeneration tank 126.
  • heat is used to reverse the chemical reaction between the H 2 S and CO 2 acid gases and the amine in order to liberate the acid gas and regenerate the amine for re-use.
  • MEA boils at 17O 0 C and atmospheric pressure, so during regeneration it is kept well below 17O 0 C in order to generally prevent amine evaporation loss. As shown in Figure 20, the absorbed water content of the amine influences the required regeneration temperature.
  • Prior art MEA applications work with a concentration of 15 to 25 weight % MEA with the balance being water, and are regenerated at temperatures between 115 0 C to 125 0 C. This large water content results in larger system fluid capacity requirements, higher capital costs associated with larger equipment and a "parasitic" energy load in order to circulate and heat this mass of water as well as the amine. This in turn results in higher operating costs.
  • the apparatus and method of the present invention operates generally anhydrous, with the only water content expected to come from equilibrium absorption through contacting the water saturated gas.
  • the minimal water content of the MEA in this process conserves both capital and operating expenses.
  • the regeneration temperature must be increased.
  • Laboratory testing has shown that 15O 0 C is an effective regeneration temperature for anhydrous MEA, and therefore is the maximum required regeneration temperature.
  • the gas cleaning apparatus 10 may alternatively be operated at a pressure greater than 1 psi, however, in order to operate at higher pressures, the gas must be compressed which increases the operating costs of the apparatus 10.
  • the contacting "surface" between the gas and the amine is generally constant because each gas bubble expelled by the bubbler pipe assembly 158 is approximately the same size.

Abstract

L’invention concerne un appareil permettant le lavage de gaz, comportant : une première cuve destinée à contenir une solution de méthyldiéthanolamine, ladite première cuve comportant une admission servant à recevoir le gaz, des tuyaux de barboteur couplés à l’admission et permettant de procéder au barbotage du gaz à travers la solution de méthyldiéthanolamine aux fins d’éliminer le sulfure d’hydrogène (H2S) dudit gaz, et une évacuation permettant d’évacuer le gaz lavé dudit H2S ; une seconde cuve destinée à contenir une solution de monoéthanolamine, ladite seconde cuve possédant une seconde admission en communication avec ladite évacuation et servant à recevoir ledit gaz lavé du H2S, des tuyaux de barboteur couplés à la seconde admission et permettant de procéder au barbotage du gaz à travers la solution de monoéthanolamine aux fins d’éliminer le dioxyde de carbone (CO2) du gaz lavé du H2S, et une seconde évacuation permettant d’évacuer le gaz lavé desdits H2S et CO2. Lesdites solutions de méthyldiéthanolamine et de monoéthanolamine sont continuellement régénérées par application de chaleur.
PCT/CA2009/000537 2008-04-29 2009-04-28 Système de barboteur pour le lavage du biogaz WO2009132424A1 (fr)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2918327A1 (fr) * 2014-03-11 2015-09-16 Abdelkader Ben Brahim Procédé d' épuration d' effluents gazeux par élimination sélective des polluants qu' ils contiennent

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA1162719A (fr) * 1980-03-31 1984-02-28 Roelof Cornelisse Methode de separation des gaz acides d'un melange gazeux fait essentiellement de methane

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA1162719A (fr) * 1980-03-31 1984-02-28 Roelof Cornelisse Methode de separation des gaz acides d'un melange gazeux fait essentiellement de methane

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2918327A1 (fr) * 2014-03-11 2015-09-16 Abdelkader Ben Brahim Procédé d' épuration d' effluents gazeux par élimination sélective des polluants qu' ils contiennent
FR3018461A1 (fr) * 2014-03-11 2015-09-18 Brahim Abdelkader Ben Procede d'epuration d'effluents gazeux par elimination selective des polluants qu'ils contiennent

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