Chemical reactors

In chemical engineering, chemical reactors are vessels designed to contain chemical reactions. The design of a chemical reactor deals with multiple aspects of chemical engineering. Chemical engineers design reactors to maximize net present value for the given reaction. Designers ensure that the reaction proceeds with the highest efficiency towards the desired output product, producing the highest yield of product while requiring the least amount of money to purchase and operate. Normal operating expenses include energy input, energy removal, raw material costs, labor, etc. Energy changes can come in the form of heating or cooling, pumping to increase pressure, frictional pressure loss (such as pressure drop across a 90^o elbow or an orifice plate), agitation, etc.

There are two main basic vessel types: a tank and a pipe.

Both types can be used as continuous reactors or batch reactors. Most commonly, reactors are run at steady-state, but can also be operated in a transient state. When a reactor is first brought back into operation (after or in operation) it would be considered to be in a transient state, where key process variables change with time. Both types of reactors may also accommodate one or more solids (reagents, catalyst, or inert materials), but the reagents and products are typically liquids and gases.

There are three main basic models used to estimate the most important process variables of different chemical reactors:

batch reactor model (batch),

continuous stirred-tank reactor model (CSTR), and

plug flow reactor model (PFR).

Furthermore, catalytic reactors require separate treatment, whether they are batch, CST, or PF reactors, as the many assumptions of the simpler models are not valid.

Key process variables include

residence time (τ, lower case Greek tau)

volume (V)

temperature (T)

pressure (P)

concentrations of chemical species (C₁, C₂, C₃,... C_n)

heat transfer coefficients (h, U)

3. Make up the plan to the text.

4. Give a brief summary of the text.

Text D

1. Read the text and choose the most suitable title out of the given ones:

a) Microfiltration membranes

b) Microfiltration

c) Membrane filters

Microfiltration is a filtration process which removes contaminants from a fluid (liquid & gas) by passage through a microporous membrane. A typical microfiltration membrane pore size range is 0.1 to 10 micrometres (µm). Microfiltration is not fundamentally different from reverse osmosis, ultrafiltration or nanofiltration, except in terms of the size of the molecules it retains.

Developed by Professor Sigmondy University of Goettingen, Germany, in 1935, membrane filters were first commercially produced by Sartorius GmbH a few years later. Membrane filters found immediate application in the field of microbiology and in particular in assessment of safe drinking water. Further development of microfilters in the mid 1970's led by the FDA's requirement for non-fibre releasing filters to be used in the production of injectable solutions. Microporous membranes are used by the micro-electronics industry as an integral part of water production. Membrane filters are widely used in biotechnology and food and beverage applications where sterile product is required.

Increasingly used in drinking water treatment, it effectively removes major pathogens, contaminants and large bacteria. For this application the filter has to be rated for 0.2 micrometres or less. For mineral and drinking water bottler the most commonly used format is pleated cartridges usually made from Polyethersulfone(PES) media. This media is asymmetric with larger pores being on the outside and smaller pores being on the inside of the filter media.

Microfiltration membranes were first introduced to the municipal water treatment market in 1987 and applied primarily to waters that were relatively easy to treat. These were cold, clear source waters that were susceptible to microbial contamination. Low pressure membranes were selected to remove turbidity spikes and pathogens without chemical conditioning. As low pressure membranes increased in acceptance and popularity, users began to apply the technology to more difficult waters which contained more solids and higher levels of dissolved organics. Some of these waters required chemical pretreatment, including pre-chlorination. These shifts in water quality triggered change in low pressure membrane technology. New products and processes were introduced to deal with higher solids and chemical compatibility.

2. Write out:

а) key words and terms;

b) the sentences expressing the main idea of each paragraph.

Unit 12

GRAMMAR: Participle I, Participle II.

1. a) Translate the following words and word combinations into Russian:

beverage, processing, to recycle, target, permeate, retentate, to depend on smth., to purify, to occur, weight, prone, fouling, to cause, solute concentration, culprit, internal pore structure, aggregation, surface, flux, reverse osmosis processes, potable water.

b) Put the words in the correct order to form sentences.

1. resembles, was, The result, radiator, which, a structure, a steam-heat.

2. over, will, the planet, become, The sky, cleaner.

3. study, The, UF processing, mainly, of, in, laboratory, occurs,.

4. help, Nowadays, power, can, the, industry, microorganisms.

5. The, known, components, that, membrane, pass, the, are, as, permeate, through.

2. Read the following sentences and translate them into Russia paying attention to the Participles. Identify the participle construction.

1. For some time bacteria must remain inactive but when container are dumped, under the action of the environment they will become activized, destroying the plastics.

2. In the future, man will be able to send enormous clouds containing earthly microorganisms.

3. Scientists have developed an original method of combating methane based on the ability of some organisms to absorb this gas.

4. The vapour emitted into the atmosphere is not harmless.

5. Air coolers functioning in many enterprises are up to date devices.

6. Water distilled in a proper way is very clear.

7. The solid separated in the filter device is called the cake.

Text A

3. Read the text and translate it using a dictionary.

Дата добавления: 2014-10-17