EP1274656A1

EP1274656A1 - Method for conditioning biogenic solid substances

Info

Publication number: EP1274656A1
Application number: EP01937982A
Authority: EP
Inventors: Reiner Numrich
Original assignee: Daub Roman; Hautz Axel
Current assignee: Daub Roman; Hautz Axel
Priority date: 2000-04-19
Filing date: 2001-04-10
Publication date: 2003-01-15
Also published as: AU6375801A; WO2001079123A1; DE10191419D2

Abstract

The aim of the invention is to provide a high calorific gas mixture that is obtained by gasifying biogenic solid substances and that is used for a combustion process, especially for use in conventional block-type thermal power stations. To this end, the product of gasification (31) is subjected to a treatment step (37) in which the solid portions contained in the product of gasification (31) are precipitated and in which the condensable portions of the product of gasification (31) mix with a liquid phase already present. The precipitated solid substances and the contaminated liquid phase are then subjected to a biological purification process and the purified gas (38) is used for combustion.

Description

CONDITIONING PROCEDURE OF BIOGENIC SOLIDS

Description:

The invention relates to a method of conditioning biogenic solids.

The disposal of waste, in particular of biogenic solids, such as sewage sludge, waste wood, organic waste and the like, is increasingly becoming a problem in terms of quantity alone.

For years, the digestive products of humans and animals have been recorded on an industrial scale via the sewage system and cleaned centrally in municipal sewage treatment plants. In addition, there are industrial wastewater, where appropriate, for which legal requirements have to be observed and checked. The increasing number of sewage treatment plants as well as their improved mode of operation also means an increasing amount of sewage sludge. In the Federal Republic of Germany, medium-term estimates assume approx. 4 million tons of dry matter from sewage sludge. With the mechanical drainage available in practically every sewage treatment plant, this means approx. 16 million tons of wet sludge, which must be disposed of annually. Currently, around 50% of sewage sludge goes to landfill or recultivation, which will no longer be possible from 2005 due to the TA municipal waste. Agricultural shipments will also tend to decline with a share of around 35%. As a result, a total of approximately 8 million tons of damp sludge will be processed annually an average drainage level of approx. 25% must be disposed of elsewhere.

There are currently 16 public mono sewage sludge incineration plants with a capacity of approx.1.6 million tons of dewatered sewage sludge per year, according to a study by the Federal Environment Agency, data on plant technology and the locations of thermal sewage sludge disposal in the Federal Republic of Germany, texts 72/98. In addition there are approx. 0.5 million tons of sewage sludge, which

Household waste incinerators to be burned with. This type of sewage sludge treatment has been a technology that has been used for years, particularly in conurbations. However, due to the increased requirements for flue gas emissions, 17.BimSchV, and the associated lack of social acceptance, there is increasing thought about the co-incineration of sewage sludge in coal-fired power plants. While dried sewage sludge is preferably used in hard coal power plants, the dewatered sewage sludge is used in lignite power plants

Mixing with lignite is used for the combustion, however, here too the emissions regulations are to be observed and complied with.

In the pyrolysis or cracking of biogenic solids, in particular waste such as preferably sewage sludge, but also of waste wood as well as other suitable biomass, the production of a gas with a high calorific value and its energetic use are in the foreground. Unrestricted use of the pyrolysis gas obtained in the pyrolysis is, however, generally prevented by impurities in the gas. The cleaning of the gas is complex and often causes the same system costs as those for the pyrolysis itself.

For energetic use, an anaerobic treatment of biogenic solids is also known, through which in the Rule from defined short chain

Hydrocarbon compounds a methane-rich gas is obtained, which can be used energetically in corresponding combined heat and power plants. Larger sewage treatment plants usually have such a treatment level. A disadvantage of this biological process is the comparatively high residual hydrocarbon content in the solid, which can only be used for energy by gasification, pyrolysis or combustion. Against this technical background, the method according to the invention makes it its task to provide a gas mixture of high calorific value obtained by gasification of biogenic solids for combustion, in particular also in conventional combined heat and power plants. In the conditioning of biogenic solids according to the invention, the method steps are based on claim 1,

- that a gasification product of the biogenic solids is fed to a treatment stage, - that in the treatment stage solids contained in the gasification product are precipitated,

- That in the treatment stage condensable portions of the gasification product mix with an existing liquid phase, - that the precipitated solids and the contaminated liquid phase of a biological cleaning and

- That the cleaned gas is fed to a combustion.

The method according to the invention has a number of advantages. These come into play particularly when existing resources can be used, for example already existing treatment stages for cleaning within a disposal facility for in particular biogenic solids. It is further contemplated that the precipitated solids and the condensed portions are biologically cleaned, likewise preferably again in a suitable device already present, for example a sewage treatment plant of the disposal device. Alternatively, the precipitated solids and the contaminated liquid phase can also remain within a closed system cycle of a disposal facility. A gas purified in this way can already be fed directly to a combustion.

It has proven particularly expedient if the gasification product of the biogenic solids is introduced into at least one biological treatment stage. In such biological treatment stages, in which, for example, rotting, fermentation, digestion or the like takes place, the solids contained in the gasification product can easily precipitate and the condensable parts of the gasification product can be mixed with the regularly present liquid phase. Cleaning of the gasification product is thus ensured in a simple, inexpensive manner.

The gases generated in the processes mentioned within the biological treatment stage will mix with the remaining purified gas fraction from the gasification and, in particular when combustible gases arise, the gas mixture obtained in this way can in particular be fed directly to the combustion.

Purification of the gasification product in such a biological treatment stage, which is usually already present in a disposal device, has an extremely favorable energy balance, in which an additional energy requirement is minimized and, if appropriate, through the combination of thermal treatment and generation of electrical energy and waste heat use is even positive.

It is further preferred in the process according to the invention that solid constituents contained in the gasification product remain in a biological treatment stage and mix with the solid ingredients still to be treated and are biologically decomposed, and that condensable parts of the gasification product mix with an existing liquid phase and are biologically decomposed.

Separate disposal of the contaminants extracted from the gasification product is therefore no longer necessary. Rather, these remain in the biological treatment stage and, as is usual there, will be biodegraded.

The inventive method is further based on the fact that

- a contaminated pyrolysis gas is introduced into a biological treatment stage, - that solid parts contained in the pyrolysis gas, e.g. Dust, remain in the biological treatment stage and mix with the solid ingredients still to be treated and are biodegraded,

- That contained in the pyrolysis gas condensable components, such as. B. oils and tars, with an existing one

Mix liquid phase and biodegradable,

- That the remaining gas fractions from the pyrolysis, in particular short-chain alkanes and alkenes, mix with methane and - and that the gas mixture thus obtained is fed, in particular, directly to the combustion in suitable combined heat and power plants. The gas mixture obtained during pyrolysis at temperatures of 600 ° C to 700 ° C with the exclusion of oxygen, then cleaned and mixed with methane, is characterized by a high calorific value and its cleanliness and can be immediately burned in a conventional combined heat and power plant or a motorized combustion for energy generation be fed.

A preferred application of the conditioning process is through integration into the process flow of a sewage treatment plant, particularly for the further disposal and recycling of sewage sludge. This is advantageously done decentrally at the location of the sludge accumulation, immediately after their mechanical dewatering. The process is also useful and economical for the comparatively low throughputs of approx. 3 t / h of dewatered sludge from small to medium-sized sewage treatment plants. The energy balance of the method according to the invention shows that no additional thermal energy is required, but rather approximately 420 kWh of electrical energy and approximately 600 kWh of low-temperature heat, e.g. be generated as process heat or for building heating per ton of sewage sludge. Extrapolated to the above-mentioned amount of sewage sludge to be thermally treated in the future, this is approximately 3.6 million MWh of electrical energy and approximately 4.8 million MWh of low-temperature heat in excess in the thermal disposal of sewage sludge.

In particular, conditioning is one in the

The sewage treatment plant itself produces digested sludge, which is first mechanically dewatered in the usual way and then subjected to full thermal drying, which can bring the water content of the pre-dried digested sludge to below 10%. The water or condensate generated during dewatering and during drying can be discharged back into the sewage treatment plant and cleaned there. For the purification of the gasification product in the conditioning process according to the invention, its introduction into a digestion tower, in particular a digestion tower for stabilizing a raw sludge of a sewage treatment plant, is suitable.

Biogenic solids can be stabilized anaerobically in digestion towers, with about 50% of the organic substance being biologically converted into methane-rich gases. This anaerobic stabilization is further promoted by the additional pressing in of the gasification products of the biogenic solids according to the invention. In particular, there is also a purification of the gasification product, from which the solid parts and the condensable parts are further removed, which remain in the digestion tower and are biologically decomposed. The gas produced by the digestion and the injected gasification product have approximately the same proportions, which means that a high-quality, natural gas-like gas mixture with a calorific value of approx. 30 MJ / kg is available.

This very pure gas mixture can flow in conventional gas engines and the electrical energy thus generated can be used to operate the sewage treatment plant or to feed it into the power grid. The waste heat from the electricity generation can expediently be used for the thermal drying of the sewage sludge and as the necessary process heat for its further treatment.

This completes the cycle of conditioning according to the invention, using the example of an integration into the process flow of a sewage treatment plant with a positive energy balance.

The efficiency of the method according to the invention can be increased further if the gasification product of biogenic solids is washed, as a result of which a considerable proportion of the condensable parts of the gasification product are already liquefied. A scrubber required for this can certainly be operated with protective water from a sewage treatment plant, for example the water from the drain of the sand trap. The washing water can then advantageously be returned to the cleaning process of the sewage treatment plant.

The method according to the invention is explained in more detail with the aid of the drawing, in which the conditioning according to the invention is only shown as an example in a sewage treatment plant. The drawing shows:

Fig. 1: a flow chart of the invention

Konditionsierung,

2: a block diagram,

Fig. 3: a mass balance based on a ton

Sewage sludge with a moisture content of TS = 35%,

Fig. 4: an energy balance, based on a ton

Sewage sludge with a moisture content of TS = 35% and

5: an analysis of a pyrolysis gas in a table.

According to FIG. 1, the sludges of a sewage treatment plant, possibly also other suitable biogenic solids, are fed in the usual way as raw sludge to anaerobic digestion in a digestion tower. With this anaerobic stabilization, approx. 50% of the organic substance in the sludge is biologically converted into a methane-rich gas.

The digested sludge is mostly mechanically dewatered, for example in a chamber filter press with the addition of slaked lime. Additionally or alternatively, dewatering can be carried out by adding flocculants, for example on a polymer basis. A TS content of 35% is achieved, which means that the loss on ignition in the dry matter with polymer conditioning is still 53%. The filter water that occurs during the mechanical drainage, in particular, is returned to the sewage treatment plant.

The dewatered sewage sludge is fed from an intermediate bunker 1, see FIG. 2, by an eccentric screw pump 2 to the thermal drying, whereby the water content of the sewage sludge can be brought to below 10%. A preheating of the sewage sludge is provided in a heat exchanger 3, which uses the low-temperature waste heat generated in the conditioning process according to the invention, indicated by the arrows 4, for example the waste heat from a combined heat and power plant 15.

In the dryer 5, the sewage sludge is fully dried to TS = 90%, a radiation belt dryer preferably being used.

The vapors 6 formed during drying are fed to a scrubber 8 with a small amount of drag air 7, in which they are cleaned and the water vapor is directly condensed. Water from the sewage treatment plant, which is fed to the scrubber 8 by means of a pump 10, can expediently be used as washing water 9. The wash water 9 is together with the vapor condensate via an intermediate container 11 as waste water 12

Wastewater treatment process fed again.

The exhaust air 13 of the scrubber 8, sucked off by a blower 14, serves in the intended complete process as secondary combustion air for a combined heat and power unit 15 and / or a pyrolysis reactor 16, the process heat of which, for example, from exhaust gases, is itself used again to dry the sewage sludge in the dryer 5 , indicated by the arrows 17, 18. If this process heat is used, then driven by a compressor 19, the heat carrier is excreted, for example, as exhaust gas 20 from the process according to the invention. The dried sewage sludge present as granules 21 is fed to the pyrolysis reactor 16, for example metered from a conveyor belt 22 via an intermediate storage in a storage container 23 and via a cellular wheel sluice 24 and exactly from a screw 25.

An indirectly heated rotary tube 26 can be provided as the pyrolysis reactor 16, for example indirectly fired by gas, indicated by a burner 27.

At temperatures of 600 ° C to 700 ° C, with the exclusion of oxygen, a calorific gas with approx. 60% short-chain alkanes and alkenes as well as approx. 10% CO and a rest of C0 ₂ and other inert gases is formed. Approx. 50% of the biogenic solid is converted into gas according to the loss on ignition of the starting substance. Table 1 summarizes the analysis values for such a gas. In particular, the low S0 ₂ content should be noted there.

After pyrolysis there remains a biologically inactive ash with a proportion of organic bound carbons that goes towards zero. This pyrolysis residue of approx. 15% to 20% of the originally present amount of dewatered sewage sludge is withdrawn from the circuit according to the invention, indicated by arrow 28, for which purpose a discharge screw 29 can be provided, for example, in which the pyrolysis residue is also cooled, and then in suitable containers 30 to be spent.

The pyrolysis gas 31 obtained in the pyrolysis is suctioned off and washed in a washer 32. This wash water 34 is taken from the sewage treatment plant by a pump 33, for example the drainage of the sand trap. In addition to washing and simultaneous cooling, water vapor portions of the pyrolysis gas 31 are also condensed out. This condensate next to the wash water is fed back to clarification according to arrow 35. The pyrolysis gas thus pre-cleaned is pumped into a digester 37 by a compressor 36. There it supports the anaerobic digestion of the sewage sludge or possibly other biogenic solids and mixes with the digester gas generated in the digestion tower 37, usually one with a high methane content. Due to the approximately equal proportions of pyrolysis gas and fermentation gas, there is a high-quality, natural gas-like gas mixture with a calorific value of approx. 30 MJ / kg.

In the digester 37, further cleaned of solids and condensable fractions, the gas mixture present there according to arrow 38 is used for energy generation, for example in the cogeneration unit 15 by combustion, to which fresh air according to arrow 39 is still to be fed regularly.

In addition to the process heat 18, such a block-type heating plant can also be used to generate energy, indicated by a generator 40.

After the raw sludge has been digested in the digester 37, the digested sludge, as explained at the beginning, is first fed to a mechanical dewatering according to arrow 41, in order then to be put down and dewatered and fed back to the intermediate bunker 1, whereby the circuit is closed.

The exhaust gases from the combined heat and power plant 15, which are also used as process heat for the radiation dryer 5, as well as the exhaust gases from the pyrolysis firing 27, can be discharged into the environment according to arrow 20 without additional cleaning, since they meet the exhaust gas values of the 17th BimSchV.

At the moment, dewatered sewage sludge from sewage treatment plants that is landfilled or otherwise used, for example in agriculture, contains around 15% of limestone that has been extinguished as a drainage aid. In the process according to the invention, liming can be omitted by using small amounts of flocculants. With additional optimization measures, the amount of sewage sludge to be treated can be further reduced by approx. 20% to 25%. In the mass balance shown in FIG. 3 and the energy balance shown in FIG. 4, 1,000 kg of digested sewage sludge of TS = 35% is subsequently assumed.

The mass flow diagram according to FIG. 3 clearly shows that the rest of the sewage sludge that is ultimately to be disposed of is reduced to 195 kg of the original amount in the form of mineral ash from the pyrolysis. 151 kg can also be used as fuel gas. The largest volume flow, a total of 654 kg from drying and pyrolysis, is returned to the circuit and cleaned after leaving the sewage treatment plant.

From the calorific value of the sewage sludge and the heating of the pyrolysis, the energy balance according to FIG. 4 shows a total of 1,496 kWh based on 1,000 kg of digested sewage sludge in primary energy. From this, 488 kWh of electrical energy can be generated by converting the pyrolysis gas into the existing combined heat and power plants. After deducting the

Own requirements remain 417 kWh for feeding into the network. 343 kWh of useful heat is also used for drying. The remaining amount of energy is divided into 126 kWh in the residual calorific value of the pyrolysis ash and 539 kWh in low-temperature waste heat, which can be used for heating purposes such as buildings, digestion, preheating, sewage sludge and the like.

If you add the gas previously obtained in the anaerobic digestion with 163 kg based on 1 ton of digested sewage sludge, there is a total of 650 kWh as useful heat after the electricity generation with a requirement of 550 kWh for drying Available. The excess electrical energy is then 1,030 kWh. The low temperature heat increases to the same extent to 1,193 kWh.

The method according to the invention thus has a positive energy balance while minimizing the residual amount to be disposed of.

conditioning methods

LIST OF REFERENCE NUMBERS

1. intermediate bunker 27. burner

2. Eccentric screw pump 40 28. Arrow 3. Heat exchanger 29. Discharge screw

4. Low temperature waste heat 30. Container

5. Dryer 31. Pyrolysis gas

6. Brothers 32. Washer

7. Tow air 45 33. Pump 8. Washer 34. Wash water

9. Wash water 35. arrow

10. Pump 36. Compressor

11. Intermediate container 37

12.Waste water 50 38. arrow 13.Exhaust air 39. arrow

14. Blower 40. Generator

15. Combined heat and power plant 41. arrow

16. Pyrolysis reactor

17.Process heat of 16 18.Process heat of 15

19. Compressor

20. Exhaust

21. Granules

22. Conveyor belt 23. Storage container

24. Cell wheel lock

25. Auger 26. Rotary tube conditioning methods

claims;

1. Conditioning process of biogenic solids, characterized by the process steps, - that a gasification product (31) of the biogenic solids (21) is fed to a treatment stage (37),

- that in the treatment stage (37) in the gasification product (31) contained solids are precipitated, - in the treatment stage (37) condensable portions of the gasification product (31) mix with an existing liquid phase,

- That the precipitated solids and the contaminated liquid phase of a biological cleaning and - That the cleaned gas (38) is fed to a combustion.

2. Conditioning method according to claim 1, characterized by the method steps, - that a gasification product (31) of the biogenic solids (21) is introduced into at least one biological treatment stage (37),

- That in a biological treatment stage (37) the gasification product (31) is cleaned and - That the cleaned gas is fed to a combustion

3. Conditioning process according to one or more of the preceding claims, characterized by the process steps,

- That a gasification product (31) of the biogenic solids (21) is introduced into at least one biological treatment stage (37), - that in a biological treatment stage (37) the gasification product (31) is cleaned and

- That the remaining gas components from the gasification mix with a gas arising in the biological treatment stage (37) and - that the gas mixture (38) thus obtained is fed to the combustion.

4. Conditioning process according to one or more of the preceding claims, characterized by the process steps,

- that a gasification product (31) is introduced into at least one biological treatment stage (37),

that the solid contents contained in the gasification product (31) remain in a biological treatment stage (37) and mix with the solid ingredients still to be treated and are biologically decomposed,

- That condensable portions of the gasification product (31) mix with an existing liquid phase and are biologically decomposed,

- That the remaining gas components from the gasification mix with a flammable gas arising in a biological treatment stage (37) and - That the gas mixture (38) thus obtained is fed to the combustion.

5. Conditioning method according to one or more of the preceding claims, characterized by the

Process steps,

- That a pyrolysis gas (31) is introduced into a biological treatment stage (37),

- That contained in the pyrolysis gas (31) solids in the biological treatment stage

(37) remain and mix with the solid ingredients still to be treated and are biodegraded,

- That condensable portions of the pyrolysis gas (31) mix with an existing liquid phase and are biologically decomposed,

- That the remaining gas from the pyrolysis mix with methane and

- That the gas mixture (38) thus obtained is fed to the combustion.

6. Conditioning method according to one or more of the preceding claims, characterized by the inclusion of conditioning in the process flow of a sewage treatment plant.

7. Conditioning method according to one or more of the preceding claims, characterized by the conditioning of a pre-dried digested sludge.

Conditioning method according to one or more of the preceding claims, characterized by cleaning the gasification product (31) in a digestion tower (37). 9. Conditioning method according to one or more of the preceding claims, characterized by cleaning the gasification product (31) in a digestion tower (37) for the stabilization of a raw sludge of a sewage treatment plant.

10. Conditioning method according to one or more of the preceding claims, characterized by cleaning the gasification product in a washer (32).

11. Conditioning method according to one or more of the preceding claims, characterized by cleaning the gasification product (31) in a washer (32) operated with dirty water (34) in a sewage treatment plant.