FR3048967A1 - DEVICE FOR THE CONTINUOUS TREATMENT OF WATER BY FLUIDIZED BED - Google Patents

Abstract

The present invention relates to a continuous water treatment device in which the treatment is provided in the presence of grains or "pellets" consisting of minerals and / or bacteria (aerobic or anaerobic) in a state of fluidization, but where the formation and growth grain is distributed in several successive reactors, each being dimensioned and adjusted precisely for a grain size, increasingly low. The residence time of water for their treatment being distributed over several successive reactors, it is possible to limit the height of each reactor by a factor of 2 to 3 compared to conventional fluidized bed reactors, which is likely to facilitate the installation of the device on certain industrial sites and also limits the energy demand for pumping.

Description

Continuous water treatment device by fluidized bed

The present invention relates to a continuous water treatment device, wherein the treatment is provided in the presence of grains or "pellets" consisting of minerals and / or bacteria (aerobic or anaerobic) in a fluidized state, but where the formation and grain growth is distributed in several successive reactors, each being dimensioned and adjusted precisely for a grain size, increasingly low.

The principle of the fluidization of a particulate material through a flowing fluid has been known for nearly a century. For a given population of particles, when the flow velocity of the fluid is sufficient, the forces of gravity and thrust of the flow are balanced and the particles are suspended in the fluid.

Some water softening processes are thus based on the formation of grains or "pellets" of calcium carbonate on fluidized particles (seeding by sand for example) and pH modification by an alkaline agent.

A second example is the elimination of phosphates, which has become an important issue in terms of health and ecology (eutrophication of water). The economic aspect (depletion of deposits) is also to be considered and today favors the search for technical and industrial solutions to recover phosphates in a crystalline form and reusable as fertilizer, especially in the form of struvite or hydroxyapatites.

Finally, in a more general way, the intimate contact between the water to be treated and the suspended solid phase not only allows specific physicochemical reactions of mineral crystallization, but also a whole range of biological treatments by various bacteria (aerobic or anaerobes according to the techniques).

In conclusion, a well-regulated fluidized water treatment device has, in principle, several specific advantages, firstly with a continuous operating mode, a low footprint and finally a production of grains or "pellets", that it is necessary to purge regularly but then try very easily.

It is known that fluidized bed reactors began to be recommended for the treatment of water in the late sixties (FR 1501912) and more and more often thereafter. The generalization of such water treatment processes encountered, however, a number of practical difficulties:

As much low fluid velocities are needed in the top of the reactors to avoid driving the fine particles out of the system, both at the base of the reactor, the same fluid must instead be introduced at a sufficient speed to move the most massive grains.

For decarbonation, for example, the particle sizes in suspension are often between 0.2 and 1.2 mm. Larger, the specific reaction surface becomes insufficient with the envisaged residence time of the water: 20-30 meters / hour (even 75 or 100 in very favorable cases), smaller, one gets closer to the operation of conventional clarifiers modified in crystallizers , with residence times imposed by a very slow kinetics of precipitation.

As a result of these constraints, the first known fluidized-bed functional reactors were of inverted conical shape, flaring more and more upwards (Fig. 1A). "Water treatment" (American 1979) Water works Association).

Some operators such as the company Ostara Nutrient Recoveiy Tech. (Canada), continue to refer to this design (Fig. IB and FIG.1C): US 2012/261334, US 2012/261338 and US 2013/334144. Nevertheless, there is no doubt that the homogeneity of the circulating flux is easier to obtain in a column of constant section, than in a section of cone, in which it can not be prevented that the velocity of the fluid in the center is somewhat greater than those near the walls. The evolution of the technique has thus seen over the years, the number of cylindrical sections increase in fluidized bed reactors: University of Columbia (Canada): US 2008/257826 (FIG. 2A), and more often separated by enlargement sections in the form of cone sections: "Enhanced Struvite Recycle from Wastewater Using a Novel Cone-Embedded Fluidized Bed Reactor": J. of Envir. Science, 2014, 26, 765-774 (FIG. 2B).

In addition, the desire to get as close as possible to the 100% water treatment with a single volume fluidized bed, led the designers to build reactors of great heights, at least 5 meters and more generally 8 at 9 meters (problem of reaction residence time), which confines these installations to large industrial sites, and which must manage large volumes.

This also poses problems of energy expenditure for pumping (gravitational energy to overcome).

Some efforts have been made to try to limit the overall height of the facilities (at least conceptually):

We first know the patent FR 2656295 of O.T.V. (Omnium of Treatment and Recovery), published in 1989, which proposes a fluidized bed decarbonation reactor, equipped in its upper part, with a section with slats inclined at 55-60 degrees and which makes it possible to lower the total height of the installation (FIG.3A)

An almost similar principle has been proposed for the recovery of phosphates (struvite), with the fluid bed material described in US Patent 2008/314838 from the University of Kansas: The apparatus has a main tubular section in a vertical position and a upper settling section oriented at an oblique angle to facilitate the sedimentation of small particles (FIG. 3B)

The problem that arises with such oblique sections of large size and / or with slats, is precisely hey sedimentation too definitive particles of unwanted sizes. This often results in fouling which requires periodic stops for maintenance. Worse still, the loss of fluidization, even local, makes lose all the theoretical advantages of the fluidized bed.

In the following pages, we describe a continuous water treatment device according to the invention, which makes it possible to solve most of the practical or energy problems resulting from the excessive height of the fluidized bed installations.

The present invention relates to a continuous water treatment device in which the treatment is provided in the presence of grains or "pellets" consisting of minerals and / or bacteria (aerobic or anaerobic), but where the formation and growth of grains is distributed in several successive reactors in fluidization state, each being dimensioned and adjusted precisely for a grain size, increasingly low.

These latter reactors can be of any type known per se, from the moment the grains are fluidized, either by the flow of the water to be treated, or by mechanical, hydraulic or gas agitation (FIG. 4A-B). ).

The device according to the invention makes it possible to avoid the main disadvantage of high installation height, since the total residence time of the water and therefore the treatment is distributed over several reactors.

According to the invention, it is firstly used a reactor sized and regulated only for the fluidization and harvesting of the largest growing grains and which allows the particles of smaller sizes to be driven to the next reactor by the fluid. Conversely, in the following reaction volumes, the fluidized grains having reached their optimum size are systematically returned to the upstream reactors.

The mechanisms for controlling and evacuating the final grains to be harvested can then be of several types known per se. For example, it can be probes, valves and chambers, and then by sieving, for example, the fluid can be separated to be returned to the reactor. For decarbonation, for example, the large particles to be collected correspond to grains between 0.4 and 1.5 mm and preferably between 0.5 and 1 mm in diameter.

By cons, an important point of the invention is that each reactor, reagents can be introduced to ensure grain growth. For example for decarbonation, it is often a question of introducing alkaline agents, whereas for the recovery of phosphates: hydroxyapatites or struvite, the main aim will be to restore in the waters to be treated a stoichiometric equilibrium for the grains to be formed.

On the contrary, a connoisseur of the prior art, noting the entrainment of granules out of the fluidized bed reactor, will rather redissolve these granules to limit the work of sedimentation of the final clarifier.

Several patents are known in which carbon dioxide or mineral acids are used to redissolve unwanted granules: patents from Ostara Nutrient recovery: US 2012/261334 and US 2012/261338.

One of the advantages that therefore results from the device with several successive reactors according to the invention is that there is very little loss of material at the final clarification stage, only very fine particles, and which result solely from the last reactor, instead of a much greater risk of loss of granules with a single reactor according to the prior art.

The residence time for the water treatment being distributed over several successive reactors according to the invention, it is above all possible to limit the height of each reactor by a factor of 2 to 3 compared to conventional fluidized bed reactors, which is likely to facilitate the installation of the device on certain industrial sites.

The energy expenditure of pumping for the water to be treated is finally greatly reduced because of this lower overall height of the device according to the invention, and may be further reduced by a slightly offset arrangement in the vertical plane of the successive reactors according to the invention. .

The overall height of the reactors decreases in favor of their diameter as the fluidification is directed at granules of smaller and smaller size (FIG. 4A-B).

An illustrative example of the softening of a drilling water according to FIG. 4A (fluidized bed, then mixed):

Claims (5)

1. Continuous water treatment device in which the treatment is provided in the presence of grains or "pellets" in fluidization state, consisting of minerals and / or bacteria (aerobic or anaerobic), but where the formation and growth of grains and therefore the treatment of water is distributed in several successive reactors. 2. Device according to claim 1, wherein the successive reactors are characterized in that the grains are fluidized by any known means, either by the flow of water to be treated, or by mechanical agitation, hydraulic or gas. 3. Device according to claims 1 and 2, characterized in that the successive reactors are dimensioned and adjusted for the fluidization of a particular population of grain size, so that the smaller size granules are naturally driven to the next reactor by the waters to be treated. 4. Device according to any one of claims 1 to 3, wherein one introduces reagents ensuring the growth of grains consisting of minerals and / or bacteria (aerobic or anaerobic), at the entrance of the device and / or at the each reactor, so that each reactor is able to ensure the growth of grains for which it is sized. 5. Device according to claim 1, characterized in that the minerals from treated water according to the invention are more particularly calcium carbonate crystals, phosphates such as struvite, hydroxyapatites.