DE4301091C1 - Utilisation of clarifier sludge for energy prodn. - by using sludge as fertiliser for growing sustainable cpds. which can be burnt to produce heat - Google Patents

Abstract

Material and energetic utilisation of clarifier sludge comprising using the sludge as fertiliser for agricultural growth of plants which can be burned to produce heat for drying the clarifier sludge. In a typical system, clarifier sludge is used as fertiliser for agricultural cultivation of renewable plants which are burned in a boiler unit together with any other organic waste to produce heat, part of which is used to dry the clarifier sludge and e.g. for district heating and part of which is converted into electricity which is used to operate the clarifier plant and excess current which is fed into the grid. Ash from the boiler is mixed with the dried clarifier sludge, and flue gas from the boiler is scrubbed to remove dust and then used to aerate the clarifier. USE/ADVANTAGE - Provides a self-supporting system for environmentally friendly disposal of clarifier sludge with prodn. of sufficient energy to operate the clarifier unit and excess energy e.g. as electricity which can be fed into the grid. Process avoids problems of disposal of clarifier sludge; is environmentally friendly; saves energy and the burning of fossil fuels; and is self-supporting w.r.t. energy and material input.

Description

Technical field

The invention is a disposal process for sewage sludge and relies on biological, chemical and thermal Connections. The procedure also covers areas of Wastewater treatment, energy production and agriculture touched.

A self-sufficient wastewater treatment plant is being implemented self-sufficient in an indirect way. The material and energy flows of an incinerator and of a biological sewage treatment plant are linked together.

State of the art

The prior art includes processes for older patent applications known that will be further developed.

The post-published DE 41 33 211 C1 describes a method for recycling of municipal and industrial sewage sludge for recultivation decommissioned agricultural and / or industrial used areas or for the production of potting soil. The sewage sludge is mechanically dewatered with organic additives (e.g. enzymes, bacteria, membrane effectors) spiked, aerobically microbially rotten and aerobic reretted. Due to the biological drying arises an earth-like substrate that adapts to its intended use with other additives (minerals, source substances or other) can be moved. As a use case for the substrate, growing is faster growing or always renewable raw materials on decommissioned agricultural and / or industrial areas called.

DE 41 09 759 C1 describes a method for integration the decontamination process of sewage sludge in its drying. The advantages are the high energy and Plant use called. With the addition of acids Flue gases and vapors from the drying facility of the Mechanical decontamination system (centrifuge, decanter) added pre-dewatered raw sludge. The mixing and the mass is heated to 70-75 ° C in a circulation system. Then the batch is mixed with a centrifuge filtered, in a mixer with dust-like waste materials mixed and the resulting granules in one Dried 115 ° C drying device. In Heavy metals that have dissolved are removed with the filtrate and used in a separate operation precipitated by calcium hydroxide. As an application for the sewage sludge prepared in this way is the recultivation of called mining tailings.

Problem areas Samples - sewage sludge disposal

The agricultural utilization of municipal sewage sludge has been a common disposal method for a long time. Sewage sludge is used as a fertilizer for plants and so returned to the natural cycle.

For some years there has been a fierce discussion about the Consequences of agricultural sewage sludge recycling used.  Enrichment of the soil with heavy metals and organic poisons are feared. It is unclear whether such Pollutants also via the plants in the food chain can reach. Food fertilized with sewage sludge and feed is hardly deductible today. Because of The relative proportion of this problem is agricultural recycled sewage sludge in the total amount produced declining. Usual disposal alternatives are currently landfill and incineration of sewage sludge. This Methods are much more expensive than agricultural ones Recovery. Long-term effects are difficult calculable. After the new TA municipal waste comes into force is practically no longer a disposal of sewage sludge possible.

It should be noted that further wastewater treatment processes, like chemical phosphate precipitation, sludge will increase in the future. Problem carriers are in primarily the municipalities as owners of wastewater treatment plants. The Disposal of sewage sludge is becoming more and more complex more expensive, wastewater fees rise.

Problem - agricultural restructuring

There is a chronic oversupply on the European market of food. The community must intervene the stocks of meat, cereals, wine and others Agricultural products do not grow uncontrollably to let.

An important method is the decommissioning of agricultural ones Acreage. But this can only be achieved when many farms are subsidized by taxpayers' money the desired sales losses to intercept financially.

The cessation of agriculture does not release farmers from your order to maintain the landscape. As part of set-aside programs is the reason for fallow fields expressly required.  

Only through suitable restructuring measures can the Agriculture reoriented in the long term become. Agriculture is gaining social value only when subsidies can be reduced.

Problem - power generation

The demand for heat and electricity in industrialized countries is high. He is essentially the combustion of fossil fuels covered in large power plants. The efficiency of such Plants decrease especially in energy conversion processes and downstream transport through long networks.

The exhaust air from combustion processes usually has to be their entry into the atmosphere. Often expensive flue gas scrubbers, filters or other types of dust separators are therefore to be connected to an incinerator.

Dust, released carbon, sulfur and nitrogen oxides pollute the environment. Incinerators work under high heat losses to the atmosphere.

Ashes and filter deposits can depend on Contain energy toxic substances. You must in individual cases be deposited in a costly manner.

Problem - Decreasing natural resources with increasing environmental pollution

The industrial goods need has developed in the economically States reached a high level. Risen accordingly is the consumption of raw materials and fossil Energy sources. Reserves are used up in short periods,  that as coal, oil, natural gas or ore over millions of years have grown naturally. Our economic Progress is threatened dramatically.

A particularly problematic consequence of overexploitation natural raw materials are increasing environmental pollution. Waste that is difficult to dispose endangers soil and groundwater; Carbon, sulfur and nitrogen oxides as well as released Thermal energy pollutes the lower atmosphere. The consequence is that "Greenhouse effect".

Process description

The method described below claims the patent for a far-reaching solution to the problems described (see above).

The starting point is sewage sludge, that of an agricultural one Recovery is supplied.

Agricultural sewage sludge utilization

Sewage sludge is broken down in accordance with legal requirements Arable land brought with renewable raw materials (Industrial plants) are ordered. Be claimed in primarily fallow land from set-aside and marginal yield soils.

The plants build organic and mineral nutrients, together with atmospheric carbon dioxide, to biomass. The energy source is sunlight. There are high-energy organic compounds like proteins, fats and carbohydrates.  

Energy generation from plants

The renewable raw materials are harvested and processed and then used energetically. Incineration or pyrolysis are the usual procedures. Power generation through the utilization of plant biomass is a well-known Method. As practiced examples are an urban one Straw incineration plant in Slagelse (Denmark) and a thermal power plant for burning wood residues from Heinrich Fahlenkamp oHG in Bruchhausen-Vilsen (Germany) call.

A combined heat and power plant to generate electricity is used as an energy system used with heat extraction. Electricity and heat are consumed in the wastewater treatment plant and possibly over proportionately short ways derived. The energy gained can be used as:

• a) Heat and district heating
  • - heating the sewage treatment plant and other buildings,
  • - delivery to a public or private network,
  • - sewage sludge drying,
• b) electrical current (cogeneration) for
  • - energetic supply of the sewage treatment plant,
  • - Delivery to a public or private network.

Treatment of combustion exhaust air

The exhaust gas flow from the incinerator becomes material and used energetically. At the same time, the cleaning of the exhaust air of dust and harmful gases, in accordance with legal requirements, reached. Here, depending on Cleaning objective and taking into account economic conditions, Dry and / or wet processes for use.  

When generating energy from renewable raw materials, it is sufficient normally a dust separation.

Exhaust air purification by separating solids

Dust becomes mechanical from the exhaust air flow (aerosuspension) or electrostatically separated. The most common systems are centrifugal force separators for dry processes (Cyclones) and filters (electrical, packed bed and fiber filters). Wet deposition processes can also be used and especially in connection with the proposed procedure prefer. Methods are spraying the exhaust air flow with liquid (heterocoagulation separation) or even better a vortex wash directly in the sewage treatment plant.

With the combustion of plant biomass there is Fly ash of the exhaust gas essentially from oxidic compounds of iron, manganese, potassium, calcium, sodium and magnesium as well as phosphorus, sulfur and nitrogen. These non-toxic After separation, substances can become dust (Dry dedusting or exhaust gas scrubbing in the sewage treatment plant) or sludge (with wet dedusting) brought to the sewage treatment plant and be treated here mechanically and biologically. At Controlled addition they carry as minerals and trace elements for the development and propagation of degradable Microorganisms. The discharge takes place in the sewage sludge.

With dry separation, the separated dust can be due to its hygroscopic properties and material composition, also used for sewage sludge conditioning become.

Sampling is required for all the disposal methods described fly ash from agricultural sewage sludge disposal secured.  

Exhaust air cleaning by gas scrubbing

If necessary, a basic wet wash can also be used the combustion exhaust air. The alkaline additive (e.g. milk of lime, caustic soda) adsorbs environmentally harmful Gases such as sulfur and carbon oxides, volatile chlorine and Hydrofluoric acid. There is a chemical conversion.

Common systems are wash towers and spray reactors. When Residual material arises, depending on the selected one Washing solution, waste water or sludge with dissolved or precipitated Salts such as gypsum, lime, calcium chloride and the like. a. The Waste water is in the connected biological treatment plant treated inexpensively. Salts are usually non-toxic and can be disposed of in an environmentally friendly way, partly can also be recycled in the sewage treatment plant. Lime can e.g. B. for pH regulation or chemical phosphate elimination be used. The discharge and sampling the residues then take place in the sewage sludge.

Both exhaust air purification processes - solids separation and gas scrubbing - can be arranged in parallel, individually or in succession. Further exhaust air purification processes, such as B. the reduction of NO _x , are not necessary, but in principle can be classified.

Oxygenation in the clarifier

The combustion exhaust air still contains approx. 10-15% atmospheric oxygen. It is either completely or as a partial flow in the clarifier directed to promote aerobic degradation processes. To call are especially

• - nitrification and
• - Degradation of organic carbon compounds.

The exhaust air discharge is therefore an artificial ventilation process.  

Wastewater heating

Exhaust air heat from the combustion process is direct or indirect (e.g. in closed heat pipes) into the clarifier headed. In addition, additional heat can arises from the burning of renewable raw materials Heat exchangers are led into the clarifier. An increase the energy content and thus the temperature of the wastewater is achieved. Technically, an energetic optimum are brought in, the endothermic biological degradation processes, as

• - aerobic degradation of organic carbon compounds,
• - biological phosphate degradation,
• - nitrification and denitrification,
• - desulphurication

favored.

Recovery of the combustion ash Sewage sludge conditioning

The ashes generated by burning plants are used to drain the sewage sludge. Because of their hygroscopic The ash is special for this suitable. Conventional conditioning agents, such as. B. Lime, including transportation costs, can be saved Landfilling of the ashes is not necessary.

Agricultural recycling

Ashes created by burning plant biomass are non-toxic. They are put up with sewage sludge brought agricultural land, so they work due to their high content of essential minerals  and trace elements extremely cheap on the Plant growth. Wood ash, for example, contains approximately 30% basic effective components as calcium oxide (CaO), which corresponds exactly the required lime-comparable composition put after the fertilizer. With 10 dt / ha wood ash Plants z. B. still 43 kg / ha of potassium oxide (K₂O) and 12th kg / ha of phosphorus pentoxide (P₂O₅) provided. Lime, Phosphorus and potash fertilizers can be obtained from agricultural Recycling combustion ash can be saved.

The entire process is illustrated using a block diagram (see drawings, Fig. 1).

Problem solving Problem solving - sewage sludge disposal

The process secures the agricultural for sewage sludge in the long term Disposal path.

Saving space for sewage sludge and incineration ash is saved. In the case of thermal sewage sludge recycling Pollutant emissions and heat emissions to the atmosphere are avoided.

The exclusive cultivation of renewable raw materials sludge-fertilized fields ensures that pollutants, such as Heavy metals and organic poisons, not in the food chain from humans and animals.

Problem solving - agriculture restructuring

Agricultural land becomes more renewable due to the cultivation Raw materials continue to be greened and maintained. The set-aside premium remains in full.  

The process ensures that many farms remain intact, jobs are preserved and government subsidies be dismantled.

Problem solving - power generation

A combined heat and power plant is used as the energy system. The efficiency lies through electricity generation with heat extraction this system at about 90% and therefore essential higher than with condensation power plants (efficiency approx. 38%). Electricity and heat are consumed in the sewage treatment plant or derived over relatively short distances, so that Transport losses can be kept low. The sewage treatment plant works without external energy.

The method is a particularly inexpensive and achieved environmentally friendly treatment of combustion exhaust air.

The release of carbon, sulfur oxides, dust and others environmentally harmful emissions to the atmosphere become clear diminished. On the one hand by the energy source, which in the In contrast to fossil substances only a small amount of sulfur contains and releases CO₂ through its growth was biochemically bound, on the other hand by elimination of exhaust gas fractions using suitable separation processes. Fly ash is treated mechanically and biologically in the sewage treatment plant and discharged over the sewage sludge or directly used in sewage sludge conditioning.

By the heat of the exhaust air flow and the heat of combustion generated become clarifiers, to promote endothermic degradation processes heated. The energy loss to the atmosphere is thereby significantly reduced.

Combustion ash becomes inexpensive when sewage sludge is conditioned used and finally as an agricultural Fertilizer used.  

Problem solving - Decreasing natural resources with increasing Ecological damage

The energetic use of plants achieves long-term that human need for energy and raw materials again in the natural balance of material structure, consumption and degradation is involved.

Through bacterial degradation and implementation processes in the Wastewater treatment plants produce low-energy inorganic raw materials. They are available to plants as ammonium, nitrate and Phosphate in sewage sludge or as carbon dioxide in the air Available. These raw materials are used in the plant high-energy organic compounds such as carbohydrates, Fats and proteins built up. Oxygen is released.

After the harvest has been processed, the plant metabolic products are in place as fuel before; a raw material that Contrary to fossil fuels are constantly renewed can.

It is important that naturally existing material and energy balances remain. This affects the nitrogen, Sulfur and phosphorus cycles, but especially the ratio of oxygen / carbon dioxide in the atmospheric Air. In contrast to burning fossil fuels are therefore not negative effects of Climate and environment to be expected.

Additional effects

The process has positive additional effects:

• 1. All waste products from the incinerator are inside the sewage treatment plant and the sewage sludge disposed of. When checking the sewage sludge before it agricultural recycling will be at the same time sampled the combustion and fly ash.  
• 2. The process improves the degradation performance of biological sewage treatment plants; The exhaust air from energy generation plants is used. Mechanisms of action are
  • - Use of exhaust air heat for heating clarifiers,
  • - Entry of minerals and trace elements in clarifiers by wet washing of combustion exhaust air or treatment of dust deposits,
  • - Artificial aeration of clarifiers through the entry of oxygen-containing combustion exhaust air.
• 3. The combustion ash becomes agricultural in the sewage sludge recycled. It acts as a mineral Fertilizer on plant development.
• 4. In combined heat and power plants, together with renewable ones Raw materials, other organic energy sources burned be, e.g. B. wood waste, selected waste fractions etc. Organic waste volumes are pushed back. However, this requires a corresponding one Approval.

Evidence of problem solutions

The problem solutions are illustrated using an exemplary embodiment proven.

The following evidence calculations are based on statistical Information on the Federal Republic of Germany, old countries from 1986 (Source: Federal Statistical Office: "Statistical Yearbook 1988", published by W. Kohlhammer GmbH Stuttgart and Mainz (1988)) unless otherwise stated.

In Germany (old federal states), 65 million m³ / a of sewage sludge are expected to be generated in 2000. This corresponds to 3.25 million t _TR / a ( _TR - dry residue). It can be assumed that one to three million hectares of agricultural land will be closed by the year 2000. For the calculation it is assumed that 1.5 million hectares of set-aside area are used to produce energy-producing plants.

proof Problem solving - sewage sludge disposal

Currently is of the following average disposal costs to go out (Source: Witte, H .: "Arguments for sewage sludge utilization", Correspondence sewage (1990) 9, Pp. 1021-1029):

• - agricultural Disposal: up to 300 DM / t _TR
• - Deposit: 400 to 600 DM / t _TR
• - Combustion: 600 to 1200 DM / t _TR

In order to calculate the benefit of the process, a sewage sludge discharge of 1 t _TR / (ha _* a) is used

1 t _TR / (ha _* a) _* 1.5 million ha = 1.5 million t _TR / a.

This results in a profit

• a) compared to landfill (average value) 1.5 million t _TR / a _* 200 DM / t _TR = 300 million DM / a,
• b) compared to incineration (average value) 1.5 million t _TR / a _* 600 DM / t _TR = 900 million DM / a.

1.5 million tonnes of _TR / a sewage sludge could be used inexpensively when growing renewable raw materials. This corresponds to approx. 45% of the total volume incurred in 2000. The profit today is between 300 and 900 million DM / a depending on the alternative disposal method (landfill or incineration).

Positive ecological effects like

• - saving of landfill space,
• - reduced pollutant emissions,
• - fewer buildings

are ignored.  

proof Problem solving - agriculture restructuring

There is currently arable land in Germany (old federal states) of around 7.3 million hectares. When calculating the reduction in subsidies it is assumed that in 2000 1.5 Million ha of set-aside area for the cultivation of renewable raw materials be available. After the cost example - fast growing trees (see above) - calculate themselves

DM 1125 / (ha _* a) _* 1.5 million ha = DM 1687.5 million / a.

Is that already calculated in the proof of problem solution 1 Share for agricultural sewage sludge disposal (Variant b) combustion) deducted, then result

(1125 - 600) DM / (ha _* a) _* 1.5 million ha = 787.5 million DM / a.

If you deduct the average set-aside premium of 600 DM / (ha _* a), there is still an annual subsidy requirement

(1125 - 600 - 600) DM / (ha _* a) _* 1.5 million ha = -112.5 million DM / a.

Analogously, without the cultivation of renewable raw materials, be used for these set-aside areas

- 600 DM / (ha _* a) _* 1.5 million ha = -900 million DM / a.

It follows that the procedure subsidies

-112.5 million DM / a - (-900 million DM / a) = +787.5 million DM / a

be dismantled. Numerous farms can use this money restructured and preserved.  

Evidence - problem solving - energy generation

On a set-aside area of 1.5 million ha, according to Example chosen above annually

25 t (ha _* a) _* 1.5 million ha = 37.5 million t / a

Biomass are generated. This corresponds to a heating value of about 15 MJ / kg wood

37.5 mt _* 15 MJ / kg = 5625 _* 10⁸ MJ.

This amount of energy covers 38.3% of the total electricity (including line losses) that occurred in 1986 in German power plants Electricity supply company was generated.

Exhaust air cleaning

The proof calculations are based on a 100% cleaning performance went out. The most unfavorable Case scheduled. That means the fly ash and sulfur dioxide accumulation is estimated as high as for the combustion an equivalent amount of fossil fuels.

60.8% of the sulfur dioxide emissions of 2.2 million t / a in Germany is at the expense of power and district heating plants. The process can be replaced by sulfur containing substitution fossil fuels and waste air purification in alkaline milieu

2.2 million t / a _* 0.608 _* 0.383 = 0.512 million t / a,

this corresponds to 23.3% of the total amount of SO₂, withheld become. When using lime milk, an im stoichiometric ratio to the expelled sulfur oxide standing amount of REA gypsum.  

15.2% of the dust emissions of 0.55 million t / a in Germany are at the expense of power and district heating plants. By the Procedures can be used for exhaust air washing in the clarifier

0.55 mt / a _* 0.152 _* 0.428 = 0.036 mt / a,

this corresponds to 6.5% of the total amount of dust in the sewage sludge held back and then disposed of agriculturally become.

The carbon dioxide balance is balanced. It will only be Liberated amount of CO₂, which in the course of growth of the Plants were bound by photosynthesis. An equivalent Energy generation from fossil fuels continues short periods of CO₂ free that by living beings in millions of years was removed from the atmosphere.

Disposal of incineration ash

In Germany (old countries) 8.915 million tons fall annually Ash, slag and soot in the production of district heating and Power on. Through the process, about 38.3% or

8.915 mt / a _* 0.383 = 3.414 mt / a

this ashes to combustion residue from renewable Raw materials. For this non-toxic waste (e.g. wood ash) costly depositing is not necessary.

It is not taken into account that renewable raw materials often have one lower ash content (approx. 0.5-2% for wood) than coal and have coke (3-18%).  

proof Problem Solving - Decreasing Natural Resources at increasing environmental pollution

If 37.5 million t / a of renewable trees with an energy content of 5625 _* 10⁸ MJ are produced (see evidence: problem solving - energy generation), they remain annually

5625 _* 10⁸ MJ: 42.705 MJ / l heating oil = 13.17 billion l

obtained with light heating oil. Under the current price conditions of 0.4 DM / l heating oil in Germany this amount a financial amount of

13.17 billion l / a _* 0.40 DM / l = 5.268 billion DM / a

The preserved amount of heating oil covers about 27% of the German one Domestic supply for one year (old countries, as of 1987). When burning renewable raw materials are in contrast balanced the balance of materials for fossil fuels. Equivalents to amounts of substance and energy are released, which are formed by the plant in assimilation processes have been. A significant reduction in the Pollutant emissions are achieved (see proof of problem solving 4 - power generation).

Claims (16)

1. Process for the material and energy recovery of sewage sludge via the production of renewable raw materials, characterized in that plants are grown on sewage sludge-fertilized fields and used for energy generation, the heat generated thereby being used for sewage sludge drying. 2. The method according to claim 1, characterized, that heat for heating buildings, clarifiers or Plants is generated. 3. The method according to claim 1, characterized, that district heating is generated. 4. The method according to claim 1, characterized, that electrical energy for self-supply of the sewage treatment plant is produced.   5. The method according to claim 1, characterized, that generates electrical energy for feeding into a network becomes. 6. The method according to claim 1, characterized, that the exhaust air flow from energy generation for Heating of clarifiers is used. 7. The method according to claim 1, characterized, that the exhaust air flow from energy generation for artificial ventilation of clarifiers is used. 8. The method according to claim 1, characterized, that the exhaust air flow from energy generation in the Sewage treatment plant is washed.   9. The method according to claim 1, characterized, that separated dust from the exhaust stream of power generation mechanical-biological in the sewage treatment plant treated and discharged over the sewage sludge. 10. The method according to claim 1, characterized, that separated dust from the exhaust stream of power generation in the sewage plant as mineral and Trace element carrier is given. 11. The method according to claim 1, characterized, that separated dust from the exhaust stream of power generation for conditioning sewage sludge is used. 12. The method according to claim 1, characterized, that separated dust from the exhaust stream of power generation agricultural together with sewage sludge is used.   13. The method according to claim 1, characterized, that ashes from energy generation for conditioning of sewage sludge is used. 14. The method according to claim 1, characterized, that ashes from energy production along with Sewage sludge is used for agriculture. 15. The method according to claim 1, characterized, that wastewater from exhaust gas purification for energy generation treated in the connected wastewater treatment plant becomes. 16. The method according to claim 1, characterized, that along with renewable raw materials others organic substances and waste in the energy system be used.