Конструкція, класифікація та принцип дії установок для глибинного культивування організмів

A → products

N_A = C_A V (where C_A is the concentration of species A, V is the volume of the reactor, N_A is the number of moles of species A)

2. ^[1]

The values of the variables, outlet concentration and residence time, in Equation 2 are major design criteria.

To model systems that do not obey the assumptions of constant temperature and a single reaction, additional dependent variables must be considered. If the system is considered to be in unsteady-state, a differential equation or a system of coupled differential equations must be solved.

CSTR's are known to be one of the systems which exhibit complex behavior such as steady-state multiplicity, limit cycles and chaos.

3. Non-ideal CSTR

The actual reaction volume will be affected by the non-uniform mixing (short-circuiting) or existence of dead zone areas. Temperature effect will also cause significant effect on the reaction rate.

Microbial fermentations received prominence during 1940's namely for the production of life saving antibiotics. Stirred tank reactor is the choice for many (more than 70%) though it is not the best. Stirred tank reactor’s have the following functions: homogenization, suspension of solids, dispersion of gas-liquid mixtures, aeration of liquid and heat exchange. The Stirred tank reactor is provided with a baffle and a rotating stirrer is attached either at the top or at the bottom of the bioreactor. The typical decision variables are: type, size, location and the number of impellers; sparger size and location. These determine the hydrodynamic pattern in the reactor, which in turn influence mixing times, mass and heat transfer coefficients, shear rates etc. The conventional fermentation is carried out in a batch mode. Since stirred tank reactors are commonly used for batch processes with slight modifications, these reactors are simple in design and easier to operate. Many of the industrial bioprocesses even today are being carried out in batch reactors though significant developments have taken place in the recent years in reactor design, the industry, still prefers stirred tanks because in case of contamination or any other substandard product formation the loss is minimal. The batch stirred tanks generally suffer due to their low volumetric productivity. The downtimes are quite large and unsteady state fermentation imposes stress to the microbial cultures due to nutritional limitations. The fed batch mode adopted in the recent years eliminates this limitation. The Stirred tank reactor’s offer excellent mixing and reasonably good mass transfer rates. The cost of operation is lower and the reactors can be used with a variety of microbial species. Since stirred tank reactor is commonly used in chemical industry the mixing concepts are well developed. Stirred tank reactor with immobilized cells is not favored generally due to attrition problems; however by separating the zone of mixing from the zone of cell culturing one can successfully operate the system.

Impellers for stirred-tank fermenters.

 

 

 

1. Rushton disc  turbine (radial flow)
2. Marine propeller (axial flow)
3. Lightin hydrofoil (axial flow)
4. Prochem hydrofoil (axial flow)
5. Intermig (axial flow)
6. Chemineer hydrofoil (axial flow)

Advantages

1. Low investment needs
2. Low operating costs

Disadvantages

               Foaming is often a problem. But this can be overcome using proper antifoaming agents. However, this has to be exercised with caution since some antifoaming agents inhibit the growth of microbes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fluidized bed reactor

A fluidized bed reactor (FBR) is a type of reactor device that can be used to carry out a variety of multiphase chemical reactions. In this type of reactor, a fluid (gas or liquid) is passed through a granular solid material (usually a catalyst possibly shaped as tiny spheres) at high enough velocities to suspend the solid and cause it to behave as though it were a fluid. This process, known as fluidization, imparts many important advantages to the FBR. As a result, the fluidized bed reactor is now used in many industrial applications.

 

Basic diagram of a fluidized bed reactor.

Basic principles

The solid substrate (the catalytic material upon which chemical species react) material in the fluidized bed reactor is typically supported by a porous plate, known as a distributor. The fluid is then forced through the distributor up through the solid material. At lower fluid velocities, the solids remain in place as the fluid passes through the voids in the material. This is known as a packed bed reactor. As the fluid velocity is increased, the reactor will reach a stage where the force of the fluid on the solids is enough to balance the weight of the solid material. This stage is known as incipient fluidization and occurs at this minimum fluidization velocity. Once this minimum velocity is surpassed, the contents of the reactor bed begin to expand and swirl around much like an agitated tank or boiling pot of water. The reactor is now a fluidized bed. Depending on the operating conditions and properties of solid phase various flow regimes can be observed in this reactor.

History and current uses

Fluidized bed reactors are a relatively new tool in the chemical engineering field. The first fluidized bed gas generator was developed by Fritz Winkler in Germany in the 1920s. One of the first United States fluidized bed reactors used in the petroleum industry was the Catalytic Cracking Unit, created in Baton Rouge, LA in 1942 by the Standard Oil Company of New Jersey (now ExxonMobil) This FBR and the many to follow were developed for the oil and petrochemical industries. Here catalysts were used to reduce petroleum to simpler compounds through a process known as cracking. The invention of this technology made it possible to significantly increase the production of various fuels in the United States.^[4] In the late 1980s, the work of Gordana V. Novakovic, Robert S. Langer, V.A. Shiva Ayyadurai and others began the use of fluidized bed reactors in biological sciences for understanding and visualizing the fluid dynamics of blood deheparinization.

Today fluidized bed reactors are still used to produce gasoline and other fuels, along with many other chemicals. Many industrially produced polymers are made using FBR technology, such as rubber, vinyl chloride, polyethylene, styrenes, and polypropylene. Various utilities also use FBR's for coal gasification, nuclear power plants, and water and waste treatment settings. Used in these applications, fluidized bed reactors allow for a cleaner, more efficient process than previous standard reactor technologies.

 

 

Advantages

The increase in fluidized bed reactor use in today's industrial world is largely due to the inherent advantages of the technology.

1. Uniform Particle Mixing: Due to the intrinsic fluid-like behavior of the solid material, fluidized beds do not experience poor mixing as in packed beds. This complete mixing allows for a uniform product that can often be hard to achieve in other reactor designs. The elimination of radial and axial concentration gradients also allows for better fluid-solid contact, which is essential for reaction efficiency and quality.
2. Uniform Temperature Gradients: Many chemical reactions require the addition or removal of heat. Local hot or cold spots within the reaction bed, often a problem in packed beds, are avoided in a fluidized situation such as an FBR. In other reactor types, these local temperature differences, especially hotspots, can result in product degradation. Thus FBRs are well suited to exothermic reactions. Researchers have also learned that the bed-to-surface heat transfer coefficients for FBRs are high.
3. Ability to Operate Reactor in Continuous State: The fluidized bed nature of these reactors allows for the ability to continuously withdraw product and introduce new reactants into the reaction vessel. Operating at a continuous process state allows manufacturers to produce their various products more efficiently due to the removal of startup conditions in batch processes.

Disadvantages

1. As in any design, the fluidized bed reactor does have it draw-backs, which any reactor designer must take into consideration.
2. Increased Reactor Vessel Size: Because of the expansion of the bed materials in the reactor, a larger vessel is often required than that for a packed bed reactor. This larger vessel means that more must be spent on initial capital costs.
3. Pumping Requirements and Pressure Drop: The requirement for the fluid to suspend the solid material necessitates that a higher fluid velocity is attained in the reactor. In order to achieve this, more pumping power and thus higher energy costs are needed. In addition, the pressure drop associated with deep beds also requires additional pumping power.
4. Particle Entrainment: The high gas velocities present in this style of reactor often result in fine particles becoming entrained in the fluid. These captured particles are then carried out of the reactor with the fluid, where they must be separated. This can be a very difficult and expensive problem to address depending on the design and function of the reactor. This may often continue to be a problem even with other entrainment reducing technologies.
5. Lack of Current Understanding: Current understanding of the actual behavior of the materials in a fluidized bed is rather limited. It is very difficult to predict and calculate the complex mass and heat flows within the bed. Due to this lack of understanding, a pilot plant for new processes is required. Even with pilot plants, the scale-up can be very difficult and may not reflect what was experienced in the pilot trial.
6. Erosion of Internal Components: The fluid-like behavior of the fine solid particles within the bed eventually results in the wear of the reactor vessel. This can require expensive maintenance and upkeep for the reaction vessel and pipes.
7. Pressure Loss Scenarios: If fluidization pressure is suddenly lost, the surface area of the bed may be suddenly reduced. This can either be an inconvenience (e.g. making bed restart difficult), or may have more serious implications, such as runaway reactions (e.g. for exothermic reactions in which heat transfer is suddenly restricted).

Current research and trends

Due to the advantages of fluidized bed reactors, a large amount of research is devoted to this technology. Most current research aims to quantify and explain the behavior of the phase interactions in the bed. Specific research topics include particle size distributions, various transfer coefficients, phase interactions, velocity and pressure effects, and computer modeling. The aim of this research is to produce more accurate models of the inner movements and phenomena of the bed. This will enable chemical engineers to design better, more efficient reactors that may effectively deal with the current disadvantages of the technology and expand the range of FBR use.

 

 

 

 

 

 

 

 

 

 

 

 

 

T

 

 

 

Trickle-bed reactor

The term Trickle Bed Reactor (TBR) entails the downward movement of a liquid and gas over a packed bed of catalyst particles. It is considered to be the simplest reactor type for performing catalytic reactions where a gas and liquid (normally both reagents) are present in the reactor and accordingly it is extensively used in processing plants. Typical examples are liquid phase hydrogenation in refineries (three phase hydrotreater) and oxidation of harmful chemical compounds in wastewater streams.

Although the physical reactor is relatively simple, the hydrodynamics in the reactor is extremely complex. It is for this reason that TBR’s have been extensively studied over the past five decades and currently the amount of open literature publications on TBR’s is increasing, hinting that the understanding of the hydrodynamics is still limited.

A good introduction to the hydrodynamics of TBR can be found in the classic article by Satterfield

Examples of process using  Trickle-bed reactor

1. Synthesis of diol products
2. Oxidative treatment of waste water
3. FCC food hydrotreating
4. Hydrogrocracking of residual oil
5. Hydrogenation of of aromatics in gasoline

Advantages

1. Close to plug flow of gas and liquid phases.
2. Small liquid phase hold-up  compared to e. g. slurry or ebulliating-bed reactors; thus suitable for minimizing homogeneous liquid phase reaction.
3. Generally simple constructions and easy operation with fixed adiabatic beds; in case of exothermic reaction gas quenches and liquid limit temperature rises.

 

Disadvantages

1. Radical dispersion of heat and mass is a problem  with highly exothermic reactions; less easy constructions as multi-tubular or internally cooled fixed beds necessary for isothermal reactor operation.
2. At low liquid velocities misdistribution, channeling and incomplete catalyst wetting occurs .
3. Particle diameter cannot usually be smaller tan 1 mm because of pressure drop consideration; intraparticle  diffusion may be limiting activity and affect selectively  adversely.
4. Counter-current operation is usually the preferred more for deep conversions, e. g., in equilibrium limited  hydrogenation, but not possible at practical velocities of gas and liquid because of danger of flooding.

 

 

 

 

 

 

 

 Bubble column reactor

 

Representation of a bubble column reactor

A bubble column reactor is an apparatus used for gas-liquid reactions first applied by Helmut Gerstenberg. It consists of vertical arranged cylindrical columns. The introduction of gas takes place at the bottom of the column and causes a turbulent stream to enable an optimum gas exchange. It is built in numerous forms of construction. The mixing is done by the gas sparging and it requires less energy than mechanical stirring. The liquid can be in parallel flow or counter-current.

Bubble column reactors are characterized by a high liquid content and a moderate phase boundary surface. The bubble column is particularly useful in reactions where the gas-liquid reaction is slow in relation to the absorption rate. This is the case for gas-liquid reactions with a Hatta number Ha <0.3.

Bubble column reactors are used in various types of chemical reactions like wet oxidation, or as Algae bioreactor. Since the computerized design of bubble columns is restricted to a few partial processes, experience in the choice of a particular type column still plays an important role.

Advantages offered by bubble column reactors:

1. efficient contact between the phases, the gas and the liquid, and eventually the third phase,, the solid catalyst
2. high liquid hold up, recommended for reactions taking place in the liquid phase (as the casee of bubble columns)
3. reasonable inter-phase mass transfer rates at low energy input
4. limitation of pressure drop
5. easy temperature control
6. little maintenance due to the simple construction
7. lack of moving parts
8. high adaptability for a specific process
9. no serious erosion and plugging problems due to the catalyst

Disadvantages of bubble column reactors

1. considerable degree of backmixing in both the liquid and the gas phase
2. short gas phase residence time
3. higher pressure drop with respect to packed columns
4. rapid decreasing of interfacial area above values of the aspect ratio greater than, due to the increased rate of coalescence

 Practical examples of reactions taking place in bubble columns and slurry reactors

1. oxidation reactions (e.g. oxidation of cyclohexane to adipic acid, partial oxidation of ethylenee to acetaldehyde, oxidation of n-parrafins to sec-alcohols)
2. hydrogenation reactions (e.g. saturation of fatty acids, hydrogenation of glucose to
3. sorbitol)
4. chlorination reactions (production of aliphatic and aromatic chlorinated compounds)
5. hydrotreating and conversion of petroleum residues
6. fermentation (production of ethanol and mammalian cells)
7. biological waste water treatment
8. oxidesulfurization of coal
9. oxichlorination of ethylene to dichlorethane
10. Fischer-Tropsch synthesis
11. methanol synthesis
12. polymerisation of olefins

 

 

AIR-LIFT FERMENTER

Airlift fermenter (ALF) is generally classified as pneumatic reactors without any mechanical stirring arrangements for mixing. The turbulence caused by the fluid flow ensures adequate mixing of the liquid. The draft tube is provided in the central section of the reactor. The introduction of the fluid (air/liquid) causes upward motion and results in circulatory flow in theentire reactor. The air/liquid velocities will be low and hence the energy consumption is also low. ALFs can be used for both free and immobilized cells. There are very few reports on ALFs for metabolite production. The advantages of Airlift reactors are the elimination of attrition effects generally encountered in mechanical agitated reactors. It is ideally suited for aerobic cultures since oxygen mass transfer coefficient are quite high in comparison to stirred tank reactors. This is ideal for SCP production from methanol as carbon substrate. This is used mainly to avoid excess heat produced during mechanical agitation.

Advantages

1. Low friction
2. Less energy requirements
3. The medical parts are easy to construct. There is no need of special aseptic seals
4. Scaling up is easier
5. Metabolic performance does not drastically reduce on scale up

Disadvantages

1. Capital needed is more
2. Difficulty of sterilization
3. Efficiently of mixing is low

 

 

 

 

 

 

 

 

 

 

 

Reference

1.Microbial Biotechnology-Fundamentals of applied Microbiology by A.N. Glazer and H.