GB2181724A

GB2181724A - Disposal of seepage water from rubbish dumps

Info

Publication number: GB2181724A
Application number: GB8623042A
Authority: GB
Inventors: Dieter Deublein; Stefan Winkler; Dieter Jansen
Original assignee: Feld & Hahn GmbH
Current assignee: Feld & Hahn GmbH
Priority date: 1985-09-25
Filing date: 1986-09-25
Publication date: 1987-04-29
Also published as: DE3534094C2; GB8623042D0; FR2587693A1; JPS6297688A; DE3534094A1

Abstract

The sludge gas (1) obtained continuously is used completely in that it is burnt in an internal combustion engine (2) which is coupled to a generator (2'), to generate current. The heat obtained in the course of this serves to heat seepage water in a heat exchanger (5) and the seepage water is evaporated in an evaporation chamber (8) by low-temperature flash evaporation under vacuum. As a result of the flash evaporation, this evaporation plant has considerable advantages over drop-film or thin-film evaporators. The encrustations otherwise usual are avoided. <IMAGE>

Description

SPECIFICATION Disposal of seepage water from rubbish dumps The invention relates to a method of disposing of seepage water from rubbish dumps using the sludge gas produced bythese dumps, and to a plantfor carrying outthis method.

Seepage water from rubbish dumps is a waste waterwhich needs particular attention in orderto protect the environment. The seepage water is pred ominantly rain water which percolates through the dump, absorbs detachable components from the rubbish in the process and emerges from the dump at its base. The components absorbed from the rubbish are mostly harmful to the ground water so thatthe seepage water should not be allowed to sink into the ground because otherwise it would endanger the ground water. For this reason, the seepage waterfrom the dumps is collected and generally brought into sewage purification plants for purifica tion.Because of the position ofthe dumps and ofthe sewage purification plants in relation to one another it is not possible, in the majority of cases, to convey the seepage water directly to the sewage purification plants. It would be even more expensive to build a special purification plant for the dumps. For these reasons, the seepage water which is collected from the dumps has to be taken to the sewage purification plants by tankers, which is very expensive.

Apart from the seepage water, gases are also obtained from the rubbish dumps, being formed during the rotting and decomposition of the waste. These gases contain predominantly CO2 and CH4. Because ofthe methane component, the gases have a calorific value which can be used to evaporate the seepage water. This is already done, gasfromthe dump being burnt directly to evaporate the seepage water. There are also methods in which the seepage water is sprayed into a combustion chamber (Aspekte der Verdampfung von Sickerwasser aus Mulldeponien mit Hilfevon Deponiegas, Mull und Abfall, 11/82, pages 314to 320).The economy of such plants is not good because the seepage water occurs in different qua ntities accordi ng to the season, while the sludge gas is available in a substantially constant amount. In addition, during conventional hot evaporation, for example in thin-film evaporators or drop-film evaporators, problems arise from encrustation by crystallized salts.

It is therefore the object of the invention to provide a method of disposing of seepage water safely and more economically.

Accordingly, the invention provides a method of evaporating seepage water from rubbish dumps using the sludge gas ofthese dumps, wherein the sludge gas is used to generate electric current, the current obtained is used to drive the machines ofthe evaporating plant and is also fed into an external electrical network, and wherein heat released during the generation of current is used to evaporate the seepage water.

By this method, the sludge gas is advantageously utilized completely, and delivers a constant amount of heat during the current-generation process. This amount of heat is always constantly available for the evaporation of seepage water regardless of its amount. The reduced quantity ofwaterwith concentrated impurities can then be carried away safely and more cheaply.

In an advantageous development of the invention, the heat obtained during the generation of current is transferred to a heat-carrier medium which is circulated through a heat exchanger. The heat-carrier medium, for example water or oil, does not reach such a high temperature that it evaporatestheseep- age water in the heat exchanger and as a result, no encrustations occur. The heat of the heat-carrier medium does heat the seepage water, however, to such an extent that evaporation occurs in the evaporation chamber as a result of the vacuum prevailing there. With this procedure, the utilization of the sludgegasisgreaterthan ifthesludgegaswereused directly to evaporate the seepage water.

Preferably, the seepage water is evaporated in an evaporation chamber by low-temperatureflash evaporation under vacuum. The concentration ofthe seepage water by flash evaporation under vacuum means that the heat can also be used at a lowtemperature level. Thus the heat produced during the generation of current by means of sludge gas is sufficient. In addition, low-temperatureflash evaporation has the advantage over the known drop-film or thin-film evaporation that encrustation on hot walls cannot occurthrough salts crystallizing out.

The seepage water which has not yet evaporated in the evaporation chamber may be circulated through the heat exchanger. Seepage water which comes from the dump is sprayed directly into the evaporation chamber, and some will evaporate immediately as a resultofthevacumm prevailing.The impurities, and a concentrated seepage water collect in a settling cone. The seepage water which is thus already preliminarily purified, is pumped offabovethesettling impurities and conveyed through the heat exchanger. Thus the risk of blockage of the heat exchanger by the impurities which have already separated out is prevented. The pumping away of the seepage water from the settling cone of the evaporation chamber further advantageously ensures a continuous constant input of seepage water to the heat exchanger.

In a further development of the invention, it is prov idedthattheconcentrated seepagewaterfromthe evaporation chamber is circulated, in the course of which the concentrate is separated out. Thus assur ance is advantageously provided that the seepage water already pre-concentrated in the settling cone is again freed of a considerable amount of liquid which is recycled to the evaporation chamber. Thus only concentrated seepage water, the concentrate, has to be transported to the sewage purification plants.

In an advantageous development of the invention, the vapours removed from the evaporation chamber are cooled in a condenserto such an extent that the condensable gases are separated from the non condensable ones. The condensable gases are cooled in the condenser by spraying in water and are precipitated as condensatewhilethe non condensable gases are drawn offthrough the vacuum pump. Since the non-condensable gases contain smelling substances, these gases may either be admixed with the sludge gas or be recycled into the dump. The condensate is pumped in circulation orconveyedthrough a cooling tower, some being continuously drawn off.

An example of a plantfor carrying out the method according to the invention is explained, with its further advantages, in more detail below with reference to the accompanying diagrammatic drawing.

Sludge gas 1 is drawn offfrom a dump and fed to an internal combustion engine 2. This internal com bustionenginemaybea piston engine oragasturb- ine, and is coupled to an electric generator 2'which generates current. The current is used to drive the plant machinery and the excess current is fed into the external network of the power supply undertaking or otherwise used usefully or stored.

Since the internal combustion engine has to be cooled, cooling water is pumped through a cooling circuit 4 by a cooling-water pump 3. Any other heat carrier medium, for example oil, may be used instead of cooling water. Connected into the cooling circuit 4 is a heat exchanger for heating the seepage water.

Seepage water 6, coming from the dump, is supp lied to an evaporation chamber 8 by a pump 7. The flow of seepage water 6 into the evaporation chamber is regulated by means of a control device 9', according to the water level in the evaporation chamber8, using a slide valve 9.

Avacuum or partial vacuum is maintained inthe evaporation chamber, so that some of the seepage water 6 pumped in will evaporate immediately, while the greater proportion collects in a settling cone 24 of the evaporation chamber. The upper layer of the accumulating seepage water is pumped by a pump 11 outofthesettlingcone24througha pipe lOintothe heat exchanger 5. There it extracts the heat from the cooling water, which may have reached 90tic, and is heated to a temperature below the boiling point at normal pressure. It is recycled to the evaporation chamber 8 where it flows out of special nozzles and evaporates in the vacuum prevailing there, as a result of the sudden expension.The vacuum necessaryfor the evaporation during the expension from the nozzles is adjusted by means of the temperature of the cooling water coming from a cooling tower 17, which water is sprayed into a co-condenser 14.

The impurities ofthe seepagewater, and the concentrated seepage water itself, collect in the settling cone 24 of the evaporation chamber 8. Despite the vacuum prevailing, this concentrated liquor does not evaporate.

After the flash evaporation, vapours saturated with water vapour leave the evaporation chamber8 through a mist collector 12 and are fed, through a vapour offlake pipe 13, to the co-condenser 14. There the condensable gases are separated from the non condensable ones. The condensable gases are cooled by water sprayed in to such an extentthat they liquifythrough condensation. The condensate which is still warm, however, is fed through a pipe 15 by means of a pump 16 into a cooling tower 17. The amount of condensate admitted into the cooling tower 17 is controlled through a control device 30'.

Excess condensate which is harmless can be con veyed to the sewerage system through a valve 30 and the pipeline 18.

The condensate is cooled in the cooling tower 17 to such an extent that it can be used as cooling waterfor the co-condenser 14. The cooled condensate is supp lied to the co-condenser by a pump 19through a re turn pipe 20.

The non-condensable gases are drawn offthrough an exhaust pipe 21 by means of a vacuum pump 22.

Since the non-condensable gases generally contain substances with an unpleasant smell, they are either recycled to the dump through a pipeline 23 or admixed with the sludge gas for burning. Thus no substances harmful to the environment emerge from the plant.

The concentrate of the seepagewatercollecting in the settling cone 24 of the evaporation chamber 8 is fed bya pump 25 through a pipeline 26to a hydro cyclone 27. The concentrated seepage water is still further concentrated in this hydro-cyclone. The overflow of recycled to the evaporation chamber 8 through a pipeline 29. The concentrated seepage water as well as precipitated impurities flow out of the cyclone cone continuously through a discharge pipe 28. It can be loaded into tanks readyfortrans port to the sewage purification plant or into other col lecting tanks or pools.

The concentration effected in the cyclone 27 may also be carried out by any other device for concentrating thin sludges, for example by separators or centrifuges.

Further treatment of the seepage-water concentrate on site, for example by further concentration or chemical treatment, can be effected in a further step independently of the plant.

Claims

1. Amethod of evaporating seepagewaterfrom rubbish dumps using the sludge gas ofthese dumps, wherein the sludge gas is used to generate electric current, the current obtained is used to drive the machines of the evaporating plant and is also fed into an external electrical network, and wherein heat released during the generation of current is used to evaporate the seepage water.

2. A method as claimed in claim 1, wherein the heat released during the generation of current is transferred to a heat carrier medium which is circulated through a heat exchanger.

3. A method as claimed in claim 2, wherein the heat carrier medium transfers its heat to the seepage water in the heat exchanger.

4. A method as claimed in any preceding claim, wherein the seepage water is evaporated in an evaporating chamber by low4emperature flash evaporation undervacuum.

5. A method as claimed in claim 4, wherein the seepage water which is not evaporated in the evaporation chamber is circulated through the heat exchanger.

6. A method as claimed in one of the preceding claims, wherein the concentrated seepagewater from the evaporation chamber is circulated, in the course ofwhich the concentrate is separated out.

7. A method as claimed in any preceding claim, wherein the vapours obtained during the evaporation of the seepage water are cooled in a condenser to such an extent that the condensable gases are separated from the non-condensable ones.

8. A plantforcarrying outthe method as claimed in claim 1,wherein an internal-combustion engine (2) for burning the sludge gas (1) is coupled to a generator (2') for generating the current and that the cooling circuit (4) of the internal-combustion engine is connected to a heat exchanger (5) which in turn is connected,through pipelines(10) to an evaporation chamber (8).

9. A plant as claimed in claim 8, wherein theevaporation chamber (8) has a settling cone (24) which is connected to a separating device (27) for concentrated seepage water, preferably a hydro-cyclone.

10. A plant as claimed in claims 8 or 9, char- acterised in that the evaporation chamber (8) comprises a vapour-offtake pipe (13) which is connected, through a condenser (14), to a vacuum pump (22).

11. A method substantially as herein described with reference to the accompanying drawings.

12. Apparatusforevaporating seepage water from rubbish dumps substantially as herein described with reference to the accompanying drawings.