EP2802540A1

EP2802540A1 - Improvements in drying processes using zeolites

Info

Publication number: EP2802540A1
Application number: EP13704830.2A
Authority: EP
Inventors: Paulus Josephus Theodorus BUSSMAN
Original assignee: Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Current assignee: Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Priority date: 2012-01-13
Filing date: 2013-01-14
Publication date: 2014-11-19
Also published as: WO2013105858A1; CN202973766U

Abstract

The invention is directed to a method and apparatus for processing a watery substance with zeolites, in particular watery substances with a relatively high water content, as well as to mixtures of zeolites and dry matter having a relatively low water content. The invention provides apparatuses and a process for processing a watery substance, such as sludge or manure, wherein the watery substance is mixed with dried matter and subsequently with zeolites, after which the mixture is dried in a mixer-drier, wherein said zeolites adsorb water from the watery substance while releasing adsorption heat which causes a further amount of moisture to evaporate from the watery substance, thus producing more dried matter, followed by a step wherein the combined dried matter is separated from the zeolites, after which the zeolites are regenerated through heating and then reused, and wherein part of said combined dried matter is recycled to the step wherein said watery substance and zeolites are mixed.

Description

Title: Improvements in drying processes using zeolites

The invention is directed to a method and apparatus for processing a watery substance with zeolites, in particular watery substances with a relatively high water content causing stickiness, as well as to mixtures of zeolites and dry matter having a relatively low water content.

WO-A-00/02822 describes a process for processing a watery substance (or slurry), such as sludge or manure, wherein the watery substance is mixed with zeolites, the mixture of zeolites and watery substance is dried in a mixer-drier, the dried matter formed by the extraction of moisture from the watery substance is separated from the zeolites, and the zeolites are reused, as well as to an apparatus for carrying out such a method.

The present inventors found that such a known process is not suitable for drying watery substances with a relatively high water content, in particular watery substances having a dry solids (ds) content of less than 55 wt.%. In particular it was found that the slurry becomes very sticky if the water content is too high. Hence when feeds are used that are too high in water content it can be quite difficult to separate the zeolites and the dried matter stream coming from the mixer-drier effectively, for instance using a screen. When the dried matter is still too wet, the zeolite and the dried matter tend to form agglomerates, thus making effective separation impossible.

Of course one could attempt to pre-concentrate the feed, prior to feeding it to a process such as described in WO-A-00/02822. However, such preconcentration steps are generally cumbersome and may add considerably to the costs.

An object of the invention is to provide an improved drying process of the type mentioned above, which enables easier recirculation of the zeolites employed, in particular by making it easier to separate the zeolites from the dried matter.

It was found that this may be achieved by mixing dry matter with the feed, in particular dry matter that is obtained from the process itself. Thus, in a first aspect, the present invention is directed to a process for processing a watery substance or slurry, such as sludge or manure, wherein the watery substance is mixed with dried matter prior to mixing it with zeolites, after which the mixture is dried in a mixer-drier, wherein said zeolites adsorb water from the watery substance while releasing adsorption heat which causes a further amount of moisture to evaporate from the watery substance, thus producing more dried matter, followed by a step wherein the combined dried matter (the dried matter obtained by drying the watery substance, combined with the dry matter added) is separated from the zeolites, after which the zeolites are regenerated through heating and then reused, and wherein part of said combined dried matter is recycled to the step wherein said watery substance and zeolites are mixed. The process of the invention can be used for any slurry, i.e. any watery suspension of solids, such as the above- mentioned sludge or manure, but also slurries that are used in food industry, such as process streams rich in carbohydrates, protein and lipids.

The zeolites used are preferably type A, also referred to as LTA (Linde Type A). Particularly suitable are NaA, KA, CaA zeolite. The zeolites adsorb water from the watery substance while releasing adsorption heat which causes a further amount of moisture to evaporate from the watery substance, and the zeolites, after the separation of the dried matter, are regenerated through heating before being recycled to the mixer-drier for reuse. Through these measures, in the mixer-drier, the watery substance to be processed is brought into a direct intensive contact with the zeolites, which, through their water selectivity, extract water from the watery substance through adsorption, by which mechanism adsorption heat is released which causes the temperature to rise, as a result of which, through evaporation of moisture, a further drying occurs. Discharging the evaporated moisture from the mixer-drier hardly, if at all, leads to off-gas problems.

The amount of zeolites to be added is dependent on factors such as the desired solids content and the desired temperature of the mixture. It was found that for a good separability of the zeolite and the dry product, in most cases the initial ds content of the feed, viz. prior to feeding it to the mixer- dryer, should be 55 wt.% or more, preferably 60 wt.% or more, more preferably 65 wt.% or more. When such a stream is fed to the mixer-dryer, this may be dried to a product comprising zeolites and dried matter, which are easily separated e.g. by sieving and wherein the resulting dried matter, after sieving (or other means of separating), is close to 100%, for instance 95 wt.% or more.

After the substance is dried to the desired value and the zeolites are separated off, the zeolites are subjected to a heating step. The previously adsorbed moisture is separated from the zeolites, and is subsequently discharged in vapor form, which entails few, if any, off-gas problems.

The separation of the mixture that comes from the mixer dryer can take place, for instance, by means of a screen. It is preferred that the zeolites are in a granulate form or a similar granular form.

Preferably zeolites are used in granular form, viz. having a largest diameter of around 0.5 to 10 mm, more preferably from 1 to 5 mm. The granules comprise the zeolites and optionally other components, such as a binder.

With the method according to the invention, due to the water adsorbing action of the zeolites, not only the off-gas problem, which is one of the objects of WO-A 00/02822 is reduced but also an efficient energy

consumption is obtained.

More particularly, with the method of to the invention, the following advantages are obtained:

- minimum off-gas amounts and hence minimal costs for off-gas treatment;

- high thermal efficiency owing to small gas flows to be heated;

- short treatment time due to direct, intensive contact, and compact equipment;

- no problems of caking onto the walls of the equipment; - high solids content at relatively low temperature;

- fire-safe due to drying in an inert granule bed;

- easy separation of zeolite and dried matter, thus resulting in a more pure product and more efficient process.

In the method according to the invention, advantageously, use can be made of the calorific value of the dried matter. If combustion air is supplied to the oven for at least partly combusting the dried matter in the mixture of zeolites and dried matter, then, depending on the organic fraction to be combusted in the dried matter, even an autothermic process can be obtained, so that the thermal efficiency of the process can be increased in that the supply of external heat can be dispensed with.

A further increase of the thermal efficiency can be obtained if the watery substance to be processed is first mechanically partly dewatered and/or preheated. This last can be done in a further advantageous manner in a pre- drier with vapor discharged from the mixer-drier, while condensate thereby formed is extracted from the mixer-drier.

The invention further relates to an apparatus for carrying out a method as contemplated in the foregoing. Figures 1 and 2 depict schematically an apparatus according to the invention. According to the invention, such an apparatus is characterized in that it comprises:

a mixer (11) having a supply for said diluted slurry (1), a supply for dried matter (5) and a discharge for slurry (2) obtained by mixing said diluted slurry (1) and said dried matter (5),

further comprising a mixer-drier (13) with mixing means and a supply for zeolites (7), a discharge for vapor (10), and a discharge for a mixture (3) obtained by said mixing means, which mixture comprises dried matter obtained by moisture extraction from said slurry,

further comprising a separator (14) comprising a supply for said mixture (3), a discharge for wet zeolites (6) and a discharge for dried matter (4), further comprising a dryer (12), comprising a supply for air (8), a discharge for wet air (9) and a discharge for zeolites (7),

further comprising a splitter (15), wherein said dried matter (4) is split into dried matter (5) which is returned to said mixer (11), and into product (P). Before or after mixer (11) a mill, such as a cone mill, may be installed (not shown) to break down large lumps into finer particles.

Figure 2 depicts an alternative embodiment, where the role of mixer (11) is performed by the first part of mixer-drier (13), so that mixer (11) is not necessary. Thus according to this embodiment zeolites and dry matter are mixed in the first part of mixer-drier (13). About half way, zeolite stream (7) is added to the mixer-drier and the rest of the process is carried out as described above.

The thermal efficiency of the apparatus can be improved if the mixer-drier is preceded by a pre-drier having a supply for sludge to be processed, a supply for vapor coming from the mixer-drier, a discharge for condensate, and a discharge for pre-heated sludge.

For similar reasons, it may further be preferred that the oven comprises a supply for combustion air and a discharge for gases, while means are present for preheating the combustion air to be supplied, with the discharged gases. Thus, both the combustion heat of the organic fraction in the dried matter is fully utilized, and a part of the heat of the discharged air is utilized for preheating the combustion air.

Referring to exemplary embodiments represented in the drawings, the method and apparatus for processing sludge according to the invention will presently be further explained, by way of example only. In the drawings, in block diagram:

Fig. 1 shows a first embodiment of an apparatus according to the invention; and

Fig. 2 shows a second embodiment of an apparatus according to the invention. Fig. 3 shows a further embodiment of the invention.

It will be clear that within the framework of the invention as set forth in the appended claims, many alterations and variants are possible.

Depending on the desired temperature in the mixer-drier, the regenerated zeolites can, if desired, be cooled before being supplied to the mixer-drier. The example given below illustrates the present invention. In particular it supports the general conclusion that to prevent the sludge from sticking to the zeolite and to be able to separate the dried sludge from the zeolite by sieving, the initial dry solid content of the wet sludge should be 55 wt.% or more. Thus, when wet feeds are used, the ds content of incoming wet sludge must be increased, which was done in the example by refluxing dried sludge (100% ds) to the wet sludge (15% ds).

Examples

The flow sheet of the process that was used in this example is shown in Figure 3. In this example a dry sohd fraction of 66% was used. To this end 1.0 ton of incoming wet sludge (15% ds, obtained from a sewage plant) was mixed with 1.5 ton of dried sludge in a first mixer E-01. This resulted net in 0.15 ton dried sludge.

The incoming wet sludge (15% ds) clearly was not suited for zeolite drying. By recycling part of the produced dry matter to the wet sludge in accordance with the present invention, the dry solid content of the feed was increased and the stickiness was avoided, thus enabling processing.

Three different sludge mixtures with different dry solid fraction were prepared:

A 50% ds was prepared by mixing 100.0 g wet sludge (15% ds) with 70.0 g dried sludge (100% ds);

a 60% ds was prepared by mixing 100.0 g wet sludge (15% ds) with 112.5 g dried sludge (100% ds); and a 70% ds was prepared by mixing 100.0 gr wet sludge (15% ds) with 183.3 gr dried sludge (100% ds).

The 50% ds mixture was still very sticky and could not be properly mixed with the zeohte; lumps were formed and the mixture was not

homogeneous. It was not possible to separate the zeolites from the dried matter using a sieve.

The 60% ds mixture had a granular structure and could well be mixed with the zeohte. In the sludge/zeolite mixture some sludge granules with an equal size of the zeolite granules can be observed. It was possible to separate the zeolites from the dried matter using a sieve.

The 70% ds mixture had a powdery structure and could very well be mixed with the zeohte. It was very easy to separate the zeolites from the dried matter using a sieve.

Claims

1. Process for processing a watery substance, such as sludge or manure, wherein the watery substance is mixed with dried matter and subsequently with zeolites in a mixer-drier, wherein said zeolites adsorb water from the watery substance while releasing adsorption heat which causes a further amount of moisture to evaporate from the watery substance, thus producing more dried matter, followed by a step wherein the combined dried matter is separated from the zeolites, after which the zeolites are regenerated through heating and then reused, and wherein part of said combined dried matter is recycled to the step wherein said watery substance and zeolites are mixed.

2. Process according to the previous claim, wherein the ds content of said mixture of combined dried matter after said mixer-drier is 55 wt.% or more, preferably 60 wt.% or more, more preferably 65 wt.% or more.

3. Process according to any of the previous claims, wherein said mixing of watery substance with dried matter is carried out in the first part of said mixture drier, and where said zeolites are added downstream to said mixture- drier.

4. Apparatus for processing a diluted slurry (1), such as sludge or manure, which comprises

further comprising a mixer-drier (13) with mixing means and a supply for zeolites (7), a discharge for vapor (10), and a discharge for a mixture (3) obtained by said mixing means, which mixture comprises dried matter obtained by moisture extraction from said slurry, further comprising a separator (14) comprising a supply for said mixture (3), a discharge for wet zeolites (6) and a discharge for dried matter (4), further comprising a dryer (12), comprising a supply for air (8), a discharge for wet air (9) and a discharge for zeolites (7),

further comprising a splitter (15), wherein said dried matter (4) is split into dried matter (5) which is returned to said mixer (11), and into product (P).

5. Apparatus according to claim 4, wherein said mixer (11) is a first part of said mixture-drier (13) and wherein said mixture drier (13) comprises a further supply for said zeolites (7).

6. Mixture comprising zeolite A in the form of granules having a size of 0.1-10 mm and dried slurry, wherein the dry solids content of the slurry (ds) is 55 wt.% or more.

7. Mixture according to the previous claim, wherein said dry solids content is 60 wt.% or more, preferably 65 wt.% or more.

8. Mixture according to claim 6 or 7, wherein said slurry is selected from sludge, manure, slurries used in food processing.

9. Mixture according to the previous claim, which is a suspension of cocoa in water.