WO2021206550A1

WO2021206550A1 - Improved auto generative pressure building anaerobic membrane bioreactor and improved working method for the production of green gas

Info

Publication number: WO2021206550A1
Application number: PCT/NL2021/050226
Authority: WO
Inventors: Christiaan Emanuel Zagt
Original assignee: Christiaan Emanuel Zagt
Priority date: 2020-04-07
Filing date: 2021-04-07
Publication date: 2021-10-14
Also published as: NL1043630B1; EP4132887A1

Abstract

The present invention concerns a system and working method for pressurized treatment of a hydrogen rich gas stream and a carbon dioxide rich water stream. The invention also includes a working method for the production of a methane gas. The system in accordance with the invention comprises: a sealable pressure vessel fitted with an inlet to supply the (to be) purified and/or treated flow, whereby the pressure vessel is equipped for oxygen-free conversion of the (to be) purified and/or treated flow in, amongst others, the execution of methane gas, at least one outlet for the removal of products from the pressure vessel, an operating system to control the process based on the relation between the produced methane gas and the supplied hydrogen gas and, in a watery stream dissolved carbon dioxide and energy generating means to control/generate useable energy with at least a part of the formed methane gas.

Description

Improved auto generative pressure building anaerobic membrane bioreactor and improved working method for the production of green gas

The present invention is related to an improved system that generates methane gas under pressure and an improved working method to produce methane gas with a suchlike system. This is based on an Auto Generative High Pressure Digestion (AHPD) installation as described earlier in the Dutch patent with number 1037103, granted on October 13th 2010 or a similar bioreactor.

In an (known) AHPD installation, green gas is produced at an auto generative (biologically) built up pressure of 12 to 25 bar. The phrase ‘green gas’ thereby refers to the fact that resources needed for the production of green gas, stem from biological origin and/or the gas is produced by means of bio catalysis. In addition, green gas mainly consists of methane and has a caloric value comparable to natural gas, enabling direct entering into the existing gas network.

An AHPD installation has the advantage that, next to methane, the likewise biologically produced carbon dioxide dissolves and/or binds better by complex forming to a higher concentration of carbon dioxide than methane in the water phase, leading to a enhanced chemical buffer capacity. This increased carbon dioxide concentration in the water phase does not cause disruptive inhibitions of the biological process to the right control.

By the earlier mentioned, under pressure induced dissolving of C0₂, this process separates the gasses methane and carbon dioxide, thereby producing relatively pure methane in the gas phase.

The pressure vessel of the installation also referred to as the bioreactor, in which the biological gas production takes place, is equipped with a recirculation pipe (which is under pressure) that drains fermenting content (anaerobe sludge) from the reactor and subsequently re-enters it into the reactor at a different spot. By doing so, the fermenting mass is mixed in the bioreactor in order to increase the response times, making the process efficient.

The recirculation pipe is provided with at least one filtration stage in which treated water (permeate) via a filter (in an economical application this would be an ultra filtration membrane) is extracted from the recirculation stream, the so-called cross flow. In a execution format, the recirculation pipe is provided with a pump, usually called ‘cross flow pump’ in order to re circulate the cross flow stream, as shown in process diagram (1).

The AHPD process includes the matching, but not part of the patent, supplementary technology regarding phosphate- and nitrogen removal, as seen in diagram 1 (process diagram and diagram 2 (microbiological diagram). The AHPD installation bears the disadvantage of a fairly complex operational management, resulting in relatively high costs per produced green gas unit. This is, amongst others caused by the filters or membranes, separating the sludge, (or the biocatalyst and the substrate, from the treated water); these can get polluted and clogged. Cleaning the filters and membranes takes time, requires additional installations and results in increased energy consumption.

Therefore, the present invention aims to provide in a system with an enhanced membrane filtration and, as a consequence, decreased use of energy, improving the efficiency of the AHPD process. This is achieved with the system according to conclusion 1 .

According to the invention, an advantage of the system is that the auto generatively built gas pressure in the AHPD installation is being used in two inventive ways in order to achieve membrane filtration for the sludge water separation (permeate production) in the cross flow, in the most efficient way.

This is primarily achieved by using the auto generative (biologically) built up pressure to push the water, which needs to be separated (permeate), through the filter membranes. This means that, while in operating state, the required trans-membrane-pressure (TMP) consequently does not have to be supplied by an additional pump and/or cross flow pump, as is the case with conventional membrane (driven) bioreactors. This also poses the advantage of a decrease in energy consumption. Therefore, the TMP is preferably set by reducing pressure in the permeate flow as is shown in diagram 3, up to a TMP of approximately 0,5 - 5 bar. This is a TMP value also common in conventional membrane bioreactors, or considerably higher, making a more efficient separation possible.

The membranes are also kept clean by generating the so-called back pulses of the permeate with the aim to push a small amount back through the membranes every now and then, using a negative TMP of 0,5 - 5 bar driving force, as is shown in diagram 3.

However, when in cleaning mode, pressure in the cross flow is temporarily decreased to a value lower than (in) the permeate, as is shown in diagram 3, whereby a limited part of the already produced permeate temporarily flows back through the membranes to the cross flow. The membranes are kept clean because the back pulse makes sure that any encrusted sludge layers are pushed back from the membranes to the cross flow and are subsequently drained together with the cross flow. Unblocking a membrane as result of a back pulse is shown in diagram 3 as a temporary increase of the viscosity of the sludge in the cross flow.

In a conventional membrane reactor, back pulses are often generated by pressurizing the permeate by means of a pulse generator - often a pump or compressor- so the necessary negative TMP is generated to clean the membrane, leading to the need for an additional installation and external energy usage. In the system as described below this is no longer required. In a design type of the system, in accordance with the invention, the system can be provided with a cross flow pump that is installed in the recirculation pipe, whereby the cross flow pump preferably is operated intermittently. The advantage of intermittent operation of the cross flow pump is the, pulse-wise, addition of an extra pressure difference that enhances the cleaning effect.

Firstly, in a low cost design type (of the system) a back pulse can be generated by alternatively turning the cross flow pump on and off; when turning on the cross flow pump, a little pressure of 1 - 3 bar is built up in addition to the biologically built up system pressure in the low cost design type 12-25 bar; when turning off the cross flow pump the permeate outflow is temporarily closed whilst the pressure in the reactor is decreased to a level under permeate pressure, whereby a likewise temporary negative TMP occurs, with a back pulse as result as is shown in diagram 3.

Secondly, in according with the invention, back pulses can be generated in the system by discontinuously releasing the produced gas, as is shown in diagram 3. As a consequence, a likewise temporary negative pressure occurs in both the reactor and the cross flow, whereby the necessary negative TMP is generated in an alternative and efficient manner.

Thirdly, membranes can be kept clean in a similar manner by generating back pulses which are the result of the periodic outflow of digested sludge from the bottom of the reactor as is shown in diagram 1 (digested dewatering); hereby also occurs temporary negative pressure in the reactor causing a back pulse.

Fourthly, a low cost design type also contains an external conventional pulse generator that uses the biologically built up gas pressure in an inventive manner in order to - using energy generating means such as an intensifier (a turbo or an a-symmetric pressure exchanger) - build up a temporary permeate pressure that is higher than the systems pressure; hence there is no need for external energy to create a back pulse.

In a design type of the system in accordance with the invention, switching between operating- and cleaning mode can be intermittently executed. The operating system of the installation according to the invention is, as described in conclusion 1 , designed for switching between operating mode and cleaning mode as is shown in diagram 3. In other words, this means that the operating system is designed to at least pulse-wise control a recirculation pump in the cross flow.

An advantage of the intermittently executing of the operating- and cleaning mode is the occurrence of an- in time varying - trans membrane pressure in the cross flow. Consequently, possible soiling on the membranes are regularly removed and are returned to the pressure vessel in the cross flow stream; additional installations for membrane cleaning are not required. In a design type of the system in accordance with the invention, multiple activities in the cleaning mode, as described above in items 1 to 4, can be combined in order to create a stronger and/or more efficient back pulse.

In the low cost design type, the cross flow is provided with a vertical pipe part through which fermenting steam is led back to the bioreactor; the flow direction from top to bottom. This vertical pipe is called the ‘ down comer ‘ (please see the red encircled area in diagram 1).

In a low cost design type hydrogen is added in this ‘down comer’ (to the process) to increase the green gas production and to decrease the carbon dioxide production.

An operating system controls the entire process and/or regulates this process based on, amongst others, the relation between the produced methane, the produced carbon dioxide, the relation between methane and carbon dioxide, the in a design type to be dosed amount of hydrogen, the pH, the temperature and the system pressure. The produced methane is collected in the gas compartment of the bioreactor in use.

Depending on, amongst others, the process settings and the added substrate, a population of micro-organisms spontaneously develop, adapted to these circumstances and function as a bio catalyst, executing various functions in four steps as is shown in diagram 2.

The activity of these biological processes, particularly the production of gasses, can, amongst others, be read from the frequency of the gas outlet in diagram 3.

In order to generate back pulses with each method, the intended parameters can be set together with the operating system such as pressure, TMP and duration of the pulse.

Further characteristics, advantages and details of the invention are described according to design types thereof, whereby reference is made to the attached drawings, in which:

Diagram 1 shows a schematic overview of an example of the system in accordance with the invention.

Diagram 2 shows a schematic overview of a microbiological diagram, showing an in use in the system occurring biological process and;

Diagram 3 shows a typical image AHPD process including cross flow with back pulse.

In an example of system 2 (diagram 1), system 2 includes pressure vessel 4, whereby pressure vessel 4 is provided with inlet 6 designated for (to be treated) organical substrate, outlet 8 for produced gas, cross flow outlet 10 which, after filtration step 14, leads to the downstream connected cross flow 12. Furthermore, pressure vessel 4 is provided with a digestate dewatering 16. Cross flow 12 is subsequently provided - in flow direction - with a riser 18, concentrate pipe 20 and down comer 22. In this example, down comer 22 is provided with a hydrogen counter flow injection 24.

In this example, system 2 further includes permeate outlet 26, which is in line provided with precipitation arrangement 28, to capture settlement of, amongst others, metals and phosphates such as zinc, lead, copper, mercury etc. and is also provided with a downstream connected ammonia remover 30, preferably an Annamox. Precipitation arrangement 28 includes in this example a phosphate remover, whereby hydrogen sulphide is produced. This is converted into sulphur under influence of C0₂. In the Annamox NH₃ is converted in N₂ and heat. The following process parameters have been used in this example: P, = 20 bar, P_CH = 18 bar, P co2 = 2 bar, T = 36 °C - 70 °C, SRT > 30 d, HRT < 10 d, ODC > 60%.

Other suitable process parameters can also be used; the above example should not be considered as limiting. During the process in this example, from outlet 8 a process stream of 90 - 98% CH₄ occurs under, for instance, 20 bar. Practice shows that, partially dependent on temperature, also other ranges, for example 85 - 98% CH₄are possible.

Diagram 2 shows four stages of anaerobe fermentation. Phase 1 is hydrolysis: this is the chemical reaction in which particles are dissolved and in which large polymers care converted into simpler monomers. Phase 2 is acidogenesis. This is a biological reaction whereby simple monomers are converted in volatile fatty acids). The third phase is acetogenesis. This is a biological reaction whereby volatile fatty acids are converted into carbon dioxide, hydrogen and acetic acid.

The fourth and last phase is methanogenesis. This is a biological reaction whereby acetates (CH₃COO ) are converted into methane and carbon dioxide, whereby hydrogen is used. Diagram 2 also shows the four phases or stages with the, therein contained, (reaction) products and (reaction) substances. References according to the below table apply:

Dutch term or name Corresponding English term 150 organisch materiaal (organic material (dead material))

152 vluchtige vetzuren (volatile fatty acids)

154 hydrolyse (hydrolysis)

156 acidogenese (acidogenesis)

158a Coprothermobacter Coprothermobacter

158b Clostridium Clostridium

158c Anaerobaculum Anaerobaculum

160 (Syntropic acetogenic bacteria (Syntropic acetogenic bacteria (SAB))

(SAB))

162 (hydrogenotrophic methanogens (hydrogenotrophic methanogens (HM))

(HM))

164 (syntropic acetate oxidation) (syntropic acetate oxidation)

166 acidogenese (acidogenesis)

168 (syntrophic acetate oxidizing (syntrophic acetate oxidizing bacteria bacteria (SAOB)) (SAOB))

170 homoacetogenese (homoacetogenesis) 172 Anaerobaculum Anaerobaculum

174 Thermacetogenium Thermacetogenium

176 methanogenese (methanogenesis)

178 (acetotrophic methanogens) (acetotrophic methanogens)

180 Methanosarcina⁺ Methanosarcina⁺

182 Methanosaeta Methanosaeta 184 Methanothermobacter Methanothermobacter 186 Methanosarcina Methanosarcina 188 Methanobrevibacter Methanobrevibacter

Tabel 1 : References diagram 2

A typical image of an AHPD process according to the invention, including cross flow and back pulse is shown in diagram 3. The lines display the aspects as shown below in table 2.

Line H shows the cross flow, whereby the cross flow pump periodically halts. Line G shows the viscosity of the sludge in the cross flow. Line F shows the variable positive trans membrane pressure (positive TMP, upward spike) and the back pulses (negative spike downwards). By periodic back pulsing, a negative TMP is generated, causing soiling in the membrane to come off which is visible in a temporary increase of the viscosity in the cross flow (spikes in line G)

The present invention is by no means limited to the above-described preferred operational form. The requested rights are determined by the subsequent conclusions, within the scope of which numerous modifications are conceivable.

Claims

Conclusions

1 . System for the production of green gas under pressure out of a (to be) purified and /or treated flow, the system of organic substrate, the system comprises:

- a pressure vessel, a (preferably) anaerobe bioreactor which is fitted for the conversion of at least a part of the substrate into green gas, with the aid of micro-organisms and devoid of oxygen, whereby auto generative pressure is build

- at least one outlet to dispose of the methane gas and or other reaction products from the pressure vessel;

- a recirculation pipe that is connected to the pressure vessel and is fitted to re-circulate the recirculation flow of a part of the substrate and/or bacteria from the pressure vessel;

- a filtration step installed in the recirculation pipe and is fitted for the pressurized extraction of permeate from the recirculation flow to a permeate outlet; and an operating system that is equipped to switch between operational- and cleaning mode, whereby in the operational mode, by means of increased gas pressure from the pressure vessel, a pre determined positive pressure drop is incorporated in the filtration step in such a manner, that permeate from the recirculation flow is transported to the permeate outlet and whereby the cleaning pressure by means of a decreased gas pressure in the pressure vessel, a pre determined negative cleaning pressure drop is incorporated in the filtration step, whereby the cleaning pressure in the reactor is lower than the pressure in the permeate outlet, so permeate is transported from the permeate outlet to the recirculation flow.

2. System according to conclusion 1 , whereby the switching between operational- and cleaning mode is preferably intermittently executed.

3. System according to conclusion 1 or 2, whereby the system is furthermore equipped with a re-circulation pump which is fitted in the recirculation pipe, whereby the recirculation pump is preferably intermittently operated.

4. System according to conclusion 1 , 2 or 3, whereby the (to be) purified and/or treated flow includes organic material from wastewater or another substrate source, and/or from hydrogen and carbon dioxide.

5. System in accordance with conclusion 1 , 2, 3 or 4, whereby the system is equipped with a gas inlet for the supply of reaction gas comprising hydrogen whereby the gas supply is installed in either the recirculation pipe or in the pressure vessel;

6. System in accordance with one of the previous conclusions, whereby the system incorporates further energy generating means that are fitted for the operation and/or generating of energy with, at least, some of the supplied reaction gas and the carbon dioxide, dissolved in substrate.

7. System in accordance with one of the previous conclusions wherein the operating system is fitted with flow regulating means in order to regulate the (to be) purified flow and/or the level in the pressure vessel.

8. System in accordance with one or more of the previous conclusions, wherein the inlet and at least one outlet are fitted with control valves and/or shut-off valves and/or check valves.

9. System in accordance with one or more of the previous conclusions, whereby the product (green gas) contains a methane concentration of at least 83%.

10. System in accordance with one or more of the previous conclusions, whereby carbon dioxide is used, (either) dissolved in water under pressure and/or chemically bound’.

11. System in accordance with one of the previous conclusions, whereby the recirculation pipe is fitted with a vertical pipe with a down stream flow direction, also called ‘ down comer’, whereby the hydrogen gas inlet is positioned in the vicinity of a bottom side of this down comer, so the reaction gas is supplied to the recirculation pipe in counter flow.

12. System in accordance with one of the previous conclusions, whereby the pressure vessel is used to grow and deploy an anaerobe population of microorganisms, adapted to pressure.

13. System in accordance with one or more of the previous conclusions, further comprising a gas buffer for green gas storage.

14. System in accordance with one or more of the previous conclusions, whereby the recirculation pipe contains a cross flow filter for the, at least partial, drainage of reaction products from the recirculation flow, whereby the reaction products preferably contain water and dissolved materials.

15. Working method for purification and/or treatment of organic waste and/or waste water comprise the following steps: - providing a system according to one or more of the previous conclusions;

- separation and draining of produced purified water from a residual stream

16. Working method according to conclusion 15, wherein the converted carbon dioxide and the produced methane gas are used to generate energy.