WO2012055405A1

WO2012055405A1 - Method for staged treatment of biomass

Info

Publication number: WO2012055405A1
Application number: PCT/DK2010/000142
Authority: WO
Inventors: Niels ØSTERGAARD; Preben Jensen
Original assignee: Westcome Renewable A/S
Priority date: 2010-10-28
Filing date: 2010-10-28
Publication date: 2012-05-03

Abstract

The invention relates to a system and method of staged treatment of biomass. The biomass is subjected to staged hydrolysis combined by cross flow release of ammonia. The system comprises a staged treatment of biomass for biogas producing plants, wherein said staged treatment comprises at least two separate hydrolysis chambers, where said biomass in said first chamber is conditioned by an air and/or a gas stream, whereby dissolved acid gases such as e.g. carbon dioxide CO₂ are stripped off, said biomass is further led to said second chamber and conditioned by an air and/or a gas stream, whereby basic gases such as e.g. ammonia NH₃ are stripped off from the biomass. The method comprises at least two separate hydrolysis steps, said first step comprises conditioning the mass by an air and/or a gas stream, whereby dissolved acid gases such as e.g. carbon dioxide CO₂ are stripped off, said biomass is further led to said second step and conditioned by an air and/or a gas stream, whereby basic gases such as e.g. ammonia NH₃ are stripped off from the biomass.

Description

Method for staged treatment of biomass

The invention relates to a system and a method of staged treatment of biomass. The biomass is subjected to staged hydrolysis combined by cross flow release of ammonia. The system comprises a staged treatment of biomass for biogas producing plants, wherein said staged treatment comprises at least two separate hydrolysis chambers, where said biomass in said first chamber is conditioned by an air or a gas stream, whereby dissolved acid gases such as e.g. carbon dioxide CO₂ are stripped off, said biomass is further led to said second chamber and conditioned by an air or a gas stream, whereby basic gases such as e.g. ammonia NH3 are stripped off from the biomass. The method comprises at least two separate hydrolysis steps, said first step comprises conditioning the mass by an air or a gas stream, whereby dissolved acid gases such as e.g. carbon dioxide CO2 are stripped off, said biomass is further led to said second step and conditioned by an air or a gas stream, whereby basic gases such as e.g. ammonia NH₃ are stripped off from the biomass.

Background

The interest of utilization of biomass has increased intensively over the past years, since biomass can help reduce the greenhouse effect because it is considered as being a C0₂ neutral fuel. In this context biomass includes manure, industrial waste, straw and organic waste or combinations thereof. Treatment of biomass to production of biogas takes place in a biogas producing plant or multiple parallel biogas producing plants where the biomass is treated in different processes. In known biogas producing plants, the processing of biomass generally takes place as a one-step treatment. To some extent a high temperature pre-treatment is used to sanitise and hydrolyse the biopolymers of the biomass and to some extent a high temperature post treatment is used to sanitise the digested biomass. Especially plants added vegetable biomass are constructed as 2-step plants having identical temperatures, where the second step works as a kind of post-digestion step.

Summary of the invention

The first aspect of the present invention concerns a system comprising a staged treatment of biomass for biogas producing plants, wherein said staged treatment comprises at least two separate chambers, where said biomass in said first chamber is conditioned by an air and/or a gas stream, whereby dissolved acid gases such as e.g. carbon dioxide CO₂ are stripped off, said biomass is further led to said second chamber and conditioned by an air and/or a gas stream, whereby basic gases such as e.g. ammonia NH3 are stripped off from the biomass.

The second aspect of the present invention concerns a method for staged treatment of biomass for biogas producing plants, wherein said staged treatment comprises at least two separate steps, said first step comprises conditioning the mass by an air and/or a gas stream, whereby dissolved acid gases such as e.g. carbon dioxide C0₂ are stripped off, said biomass is further led to said second step and conditioned by an air and/or a gas stream, whereby basic gases such as e.g. ammonia NH₃ are stripped off from the biomass.

Brief description of the drawing

Figure 1 shows one embodiment of the system according to the invention.

Detailed description of the invention

The first aspect of the present invention concerns a system comprising a staged treatment of biomass for biogas producing plants, wherein said staged treatment comprises at least two separate chambers, where said biomass in said first chamber is conditioned by an air and/or a gas stream, whereby dissolved acid gases such as e.g. carbon dioxide C0₂ are stripped off, said biomass is further led to said second chamber and conditioned by an air and/or a gas stream, whereby basic gases such as e.g. ammonia NH₃ are stripped off from the biomass. The invention can be used on any kind of biogas producing plant or similar plant for treatment of liquid and / or liquefied mass, where one wishes to enhance the conversion of organic mass to biogas or similar, without the need of adding additional biomass. Biomass can include manure, industrial waste, straw and organic waste or similar or combinations thereof.

The second aspect of the present invention concerns a method for staged treatment of biomass for biogas producing plants, wherein said staged treatment comprises at least two separate steps, said first step comprises conditioning the mass by an air and/or a gas stream, whereby dissolved acid gases such as e.g. carbon dioxide CO₂ are stripped off, said biomass is further led to said second step and conditioned by an air and/or a gas stream, whereby basic gases such as e.g. ammonia NH₃ are stripped off from the biomass.

By using stepwise division of the system and method according to the two aspects of the invention, selection of the different processes in the process chambers can be carried out. By separating the simple processes optimal conditions for the single process are obtained. Thereby it can be secured that the different processes have optimal and controllable conditions. Such optimal and controllable conditions can e.g. be dimension of the chamber regarding both geometry and mechanic and also circulation and stirring of liquid and / or liquefied mass, construction of the headspace, strain of the headspace, temperature in the headspace and flushing with conditioned gas and/or air. This new technique gives the opportunity to adjust all the variables in the separate hydrolysis chambers of the staged treatment to the current changes in the mass that has to be treated. Thereby a very effective operation through the chambers of the staged treatment can be obtained - whichever kind of mass is being led through the system. This makes the entire system very effective and results in a substantial increase in yield, also when the mass has a short treatment time in the chambers. The invention ensures a high level of hygiene and decomposition of infectious substance, since some bacteria, viruses and parasites die relatively fast when heated to 70°C or more, whereby the treated mass is not only usable for production of biogas or similar, but could also be used as a source for biologic de-nitrification and similar processes and as a fertiliser for use on farmland without veterinarian restrictions.

In one embodiment of the first aspect of the invention the system further comprises at least one reaction tank where the biomass is at least partly converted to biogas by digestion within the temperature range of 30 - 55°C.

In one embodiment of the first aspect of the invention the system further comprises at least one separator for separating the biomass in particles and liquids. In one embodiment of the first aspect of the invention the separation of particles and liquids can be individually decided based on particle size.

In one embodiment of the method according to the second aspect of the invention the biomass is at least partly converted to biogas by digestion within the temperature range of 30 - 55°C in a reaction tank before the staged treatment is taking place. In one embodiment of the method according to the second aspect of the invention the biomass is separated into particles and liquids based on particle size.

Figure 1 displays how the staged treatment of biomass can be implemented into a biogas producing plant. Liquefied biomass is pumped via a pipeline 101 to the reaction tank 103. In the reaction tank 103 a part of the organic mass is converted to biogas by digestion within the temperature range of 30 - 55°C. The treated biomass can be led from the reaction tank 103 via a pipeline 105 to a separator 107, where a separation of particles and liquids is taking place. This separation of particles and liquids can be individually decided based on particle size. In one embodiment of the invention a polymer and/or a precipitant can be added before the separation takes place. This enables that the size of the particles increases, whereby the flow of • mass to the following hydrolysis increases. The particles are directed via a pipeline 109 towards the staged treatment of biomass whereas the liquid from the separator can be directed to another use, e.g. de-nitrification via a pipeline 111. Alternatively the treated biomass can be directly led towards the staged treatment of biomass from the reaction tank 103 via a pipeline 113, thereby skipping the separation of liquids from particles. Before entering the staged treatment the biomass is directed into a heat exchanger 115, where the biomass is heated to hydrolysis temperature before being transferred into the first chamber 117 of the staged treatment. The energy consumption of heating the biomass in the heat exchanger is less when the biomass has a high content of dry matter particles than when the biomass has a higher content of liquid. Therefore the step of separation of particles and liquids in a separator can be an effective way of reducing energy consumption in a biogas producing plant. In the first chamber the mass is being conditioned by inlet of air or a gas stream 119 into the chamber. By conditioning the mass by an air or a gas stream, the result is stripping off acid gases such as e.g. carbon dioxide CO₂ and hydrogen sulphide H₂S from the biomass. The acid gases leave the chamber at 121 by a pipeline. By performing this conditioning of the biomass the pH of the mass increases significantly, usually from between 7.5 and 8.0 up to between 8.5 and 9.5. The conditioned mass with the high pH is further led to the second chamber 123 of the staged treatment. In the second chamber the mass is being conditioned by inlet of air or a gas stream 125 into the chamber. By conditioning the mass by an air or a gas stream, the result is stripping off basic gases such as e.g. ammonia NH₃ from the biomass. The basic gases leave the chamber at 127 by a pipeline. By performing this conditioning where the content of ammonia in the biomass decreases, the pH of the mass is decreased significantly, usually between 0.5 to 1 pH units. The conditioned mass with the lower pH is afterwards led to the third chamber 129 of the staged treatment by the pipeline 131 or led to subsequent treatment by the pipeline 133. In the third chamber a bacterial growth is initiated. The bacterial growth results in that acidification and hydrolysis of the biomass occur since the concentration of ammonia is low. The result is production of carbon dioxide CO2 which is released through pipeline 137 assisted by inlet of air or gas into the chamber at 135. After leaving the third chamber the mass is led to subsequent treatment by the pipeline 139.

In one embodiment according to the first aspect of the invention the system further comprises at least one heat exchanger where the treated mass is cooled by transferring heat to the colder mass being led counter-currently through the heat exchanger on its way to the staged treatment, whereby the cold mass is heated to hydrolysis temperature before being transferred into the first chamber of the staged treatment.

In one embodiment according to the second aspect of the invention the treated mass is cooled by transferring heat to the colder mass being led counter-currently through a heat exchanger on its way to the staged treatment, whereby the cold mass is heated to hydrolysis temperature before being transferred into the first chamber of the staged treatment.

The hydrolyzed and ammonia poor mass from pipeline 139 and/or pipeline 133 is cooled in the heat exchanger 115 to a temperature of around 35 - 55°C. The hot hydrolyzed and ammonia poor mass is cooled by transferring heat to the colder mass being led counter-currently through the heat exchanger on its way to the staged treatment. At temperatures of around 35 - 55°C the biogas producing bacteria thrive. The mass is cooled further if the mass has to be used for other things. The treated cooled mass is directed towards a separator 141 by pipeline 143, where it is separated into particles 145 and liquid 147. The liquid from the separator is directed to another use, e.g. de-nitrification via a pipeline. Alternatively, the treated biomass can be directed around the separator by a pipeline 149. The cooled and treated mass is directed towards reaction tank 103 by pipeline 151 or towards a second reaction tank 153 by pipeline 155 where the mass is further treated by digestion within the temperature range of 30 - 55°C under production of biogas 157. The cooled and treated mass can alternatively be transferred to another use, e.g. de-nitrification via a pipeline 159.

In the following, the staged treatment of biomass will be described in more details. In this description the staged treatment is divided into three steps, but the staged treatment could also comprise only two steps - or more additional steps could also be implemented.

In one embodiment according to the second aspect of the invention the method comprises an accumulation of organic material in said first step which induces a gelatinisation of said organic material in the mass followed by deamination of the organically bound nitrogen to free ammonia. In the first chamber the treated biomass is being conditioned by inlet of air or a gas stream into the chamber via a headspace. The organic nitrogen present in the mass will be exposed to microbial deamination whereby formation of ammonia occurs. Also, a gelatinisation of the carbohydrates in the mass occurs in this first chamber. By conditioning the mass by an air or a gas stream, the result is stripping off dissolved acid gases such as e.g. carbon dioxide CO₂ and hydrogen sulphide H₂S from the biomass. The acid gases leave the chamber by a pipeline. By stripping off acid gases, in particular CO_2, an accumulation of organic material occurs which induces an improved gelatinisation of organic material in the mass, which again establishes the basis for the following deamination of the organically bound nitrogen. The accumulation of organic material also induces an improved hydrolysis compared to the standards known today. By performing this conditioning of the biomass, the pH of the mass increases significantly up to around 9.5 due to the condition treatments of the first chamber. This high pH value is necessary for achievement of an effective stripping of ammonia in the second chamber.

In an embodiment according to the first aspect of the invention or in an embodiment according to the second aspect of the invention the high concentration of organic material can be concentrated and accumulated in a sludge phase or particle phase which can have a longer retention time in the first chamber than the liquid. Thereby the liquid can have a short treatment time, whereas the particles can have a longer treatment time in the first chamber of the staged treatment.

The liquid can be transferred from the first chamber to the second chamber and from the second chamber to the third chamber and from the third chamber and further in the system for subsequent treatment independently of the sludge phase or particle phase - and also independently of the amount of biomass led into the staged treatment at the first chamber and the amount of biomass led out of the staged treatment at the last chamber in line of the staged treatment. Thereby the liquid phase which has a low buffer capacity can be led faster through the staged treatment than the sludge phase or particle phase. This split up of the biomass in liquid phase and sludge phase or particle phase gives the bacteria better environmental conditions in the chambers, resulting in a higher efficiency of the system.

In the second chamber the conditioned mass with the high pH is further treated. In the second chamber the mass is also being conditioned via headspace treatment by inlet of air or a gas stream into the chamber. By conditioning the mass by an air or a gas stream, the result is stripping off basic gases such as e.g. ammonia NH₃ from the biomass. Since the carbon dioxide is no longer binding the ammonia, the ammonia can easier be stripped off. The basic gases leave the chamber by a pipeline. By performing this conditioning where the content of ammonia in the biomass decreases, the pH of the mass decreases to around 8 - 8.5. By being able to expel a substantial amount of ammonia from the second chamber, the bacterial growth can enhance since the ammonia is not inhibiting the growth - and also formation of enzymes that can degradate the organic material can increase.

In one embodiment of the first aspect of the invention the staged treatment of biomass further comprises a third chamber, where said biomass in said third chamber is conditioned by an air and/or a gas stream, whereby the production of carbon dioxide C0₂ is stripped off.

In one embodiment of the first aspect of the invention the biomass in said third chamber can be concentrated and accumulated in a sludge phase which can have a longer retention time in the third chamber, whereas the liquid can have a short treatment time in the third chamber of the staged treatment. In one embodiment of the second aspect of the invention the method further comprises a third step, where said biomass in said third step is conditioned by an air and/or a gas stream, whereby the production of carbon dioxide CO₂ is stripped off.

In one embodiment of the second aspect of the invention the biomass in said third chamber can be concentrated and accumulated in a sludge phase which can have a longer retention time in the third chamber, whereas the liquid can have a short treatment time in the third chamber of the staged treatment.

In one embodiment of the second aspect of the invention the method comprises a bacterial hydrolysis of the neutralized biomass. This occurs since the concentration of ammonia is low.

In one embodiment of the second aspect of the invention the method comprises that gelatinized carbohydrates in the biomass are attacked by the bacteria whereby in part low polymeric components, different sugar species and volatile species are generated which are easy to convert for the bacteria, followed by further gelatinisation induced by enzymatic degradation of the partly gelatinized and crystalline particles present in the mass.

In the third chamber the conditioned mass with the low pH is further treated. The conditioned mass could also skip the third step of the treatment and be led directly to subsequent treatment by a pipeline. In the third chamber a bacterial growth is initiated. The bacterial growth results in that a bacterial hydrolysis of the neutralized biomass occurs since the concentration of ammonia is low. The gelatinized carbohydrates are attacked by the bacteria whereby in part low polymeric components, different sugar species and volatile species are generated which are easy to convert for the bacteria. Afterwards, further gelatinisation is induced by enzymatic degradation of the partly gelatinized and crystalline structures/particles present in the mass. The result is production of carbon dioxide CO₂ which is released through a pipeline assisted by headspace inlet of air or gas into the chamber. After leaving the third chamber the mass is led to subsequent treatment by a pipeline. The particles can be concentrated and accumulated in a sludge phase or particle phase which can have a longer retention time in the third hydrolysis chamber than the liquid. Thereby the liquid can have a short treatment time, whereas the particles can have a longer treatment time in the third chamber of the staged treatment.

The anaerobic hydrolysis taking place in the chambers described above happens within the temperature range of 70 - 100°C in a preferred embodiment and lasts between 15 minutes to 24 hours in a preferred embodiment of the invention.

In an embodiment according to the first aspect of the invention or in an embodiment according to the second aspect of the invention the anaerobic hydrolysis takes place at a pressure similar to the saturation pressure of water vapour at least through a period of the hydrolysis.

In an embodiment according to the first aspect of the invention or in an embodiment according to the second aspect of the invention the pressure of at least one of the hydrolysis chambers is above 1 atmosphere. In an embodiment according to the first aspect of the invention or in an embodiment according to the second aspect of the invention the conditioning of the mass in the chambers described above happens via separate headspace treatments by inlet of air and/or a gas stream into the separate chambers. Thereby the inlet of air or a gas stream into e.g. the first chamber can be different from the inlet of air or a gas stream into e.g. the second chamber and/or the third chamber. The difference in headspace treatment in the chambers can be both regarding the amount and composition of the air and/or gas.

The staged treatment of a mass, presented in this application, is not possible to carry out in one chamber, even if the volume of that chamber is increased, since it is not possible to control and secure that the individual stages of treatment are completed before the next step in the treatment starts. If all the processes have to be accomplished in one chamber, the individual substances, e.g. the carbon dioxide and the ammonia, will react with each other.

The following is a reaction that could occur, if the processes where to be carried out in one chamber: C0₂ + H₂0→ H₂CO₃

H₂C0₃ <→ HCO3^" + H⁺ <→ C0₃ ^" + 2H⁺

NH₃ + H⁺→NH₄ ⁺

HCO3^" + NH₄ ⁺→ NH₅C0₃

The product NH₅CO₃ is an easily soluble salt.

If all the processes take place in one chamber at temperatures of around 70 - 95°C the thermal movements in the gas phase will be substantial, whereby it would be impractical to strip off the individual components from the gas phase. The ammonia will bind to the carbon dioxide, whereby neither of the two gases can easily be stripped off.

With the present invention it is possible to split the treatment into different phases, which enables selective operating procedures in the individual steps of treatment. By separating the individual processes optimal conditions for the single process are obtained, which in the end results in a streamlining of the entire system.

Compared to prior art, the system of the present invention comprises splitting the treatment into different phases just as it comprises selective headspace treatment in the individual phases to maximise the efficiency of the treatment. Further, the dimensions and construction of the individual chambers are optimized for the process that takes place inside that chamber - e.g. by establishing parallel air and/or gas inlet stream to the individual chamber whereby the amount and content of air and gas to the individual chamber can be decided.

References

101 pipeline

103 reaction tank

105 pipeline

107 separator

109 pipeline

111 pipeline

113 pipeline

115 heat exchanger

117 first chamber

119 inlet of air and/or a gas stream

121 pipeline

123 second chamber

125 inlet of air and/or a gas stream

127 pipeline

129 third chamber

131 pipeline

135 inlet of air and/or a gas stream

137 pipeline

139 pipeline

141 separator

143 pipeline

145 pipeline

147 pipeline

149 pipeline

151 pipeline

153 reaction tank

155 pipeline

157 pipeline

159 pipeline

Claims

1. A system comprising a staged treatment of biomass for biogas producing plants, wherein said staged treatment comprises at least two separate chambers, where said biomass in said first chamber is conditioned by an air and/or a gas stream, whereby dissolved acid gases such as e.g. carbon dioxide C0₂ are stripped off, said biomass is further led to said second chamber and conditioned by an air and/or a gas stream, whereby basic gases such as e.g. ammonia NH₃ are stripped off from the biomass.

2. A system according to claim 1 wherein the biomass in said first chamber can be concentrated and accumulated in a sludge phase which can have a longer retention time in said first chamber, whereas the liquid can have a short treatment time in said first chamber of the staged treatment.

3. A system according to anyone of claims 1-2, wherein the staged treatment of biomass further comprises a third chamber, where said biomass in said third chamber is conditioned by an air and/or a gas stream, whereby the production of carbon dioxide CO₂ is stripped off.

4. A system according to claim 3, wherein the biomass in said third chamber can be concentrated and accumulated in a sludge phase which can have a longer retention time in the third chamber, whereas the liquid can have a short treatment time in the third chamber of the staged treatment.

5. A system according to anyone of claims 1-4, wherein the conditioning of the biomass in the chambers is conducted via separate headspace treatments by inlet of air and/or a gas stream into the separate chambers.

6. A system according to anyone of claims 1-5, wherein the system further comprises at least one reaction tank where said biomass is at least partly converted to biogas by digestion within the temperature range of 30 - 55°C.

7. A system according to anyone of claims 1-6, wherein the system further comprises at least one separator for separating the biomass in particles and liquids.

8. A system according to claim 7, where the separation of particles and liquids can be individually decided based on particle size.

9. A system according to anyone of claims 1-8, wherein the system further comprises at least one heat exchanger where the treated mass is cooled by transferring heat to the colder mass being led counter-currently through the heat exchanger on its way to the staged treatment whereby the cold mass is heated to hydrolysis temperature before being transferred into the first chamber of the staged treatment.

10. A method for staged treatment of biomass for biogas producing plants, wherein said staged treatment comprises at least two separate steps, said first step comprises conditioning the mass by an air and/or a gas stream, whereby dissolved acid gases such as e.g. carbon dioxide CO₂ are stripped off, said biomass is further led to said second step and conditioned by an air and/or a gas stream, whereby basic gases such as e.g. ammonia NH₃ are stripped off from the biomass.

11. A method according to claim 10, comprising an accumulation of organic material in said first step which induces a gelatinisation of said organic material in the mass followed by deamination of the organically bound nitrogen to free ammonia.

12. A method according to anyone of claims 10-11 , where the biomass in said first step is concentrated and accumulated in a sludge phase which has a longer retention time in the first chamber, whereas the liquid has a short treatment time in the first chamber of the staged treatment.

13. A method according to anyone of claims 10-12, where the method further comprises a third step, where said biomass in said third step is conditioned by an air and/or a gas stream, whereby the production of carbon dioxide CO₂ is stripped off.

14. A method according to claim 13, comprising a bacterial hydrolysis of the neutralized biomass.

15. A method according to any one of claims 13-14, where gelatinized carbohydrates in the biomass are attacked by the bacteria whereby in part low polymeric components, different sugar species and volatile species are generated which are easy to convert for the bacteria, followed by further gelatinisation induced by enzymatic degradation of the partly gelatinized and crystalline particles present in the mass.