Examination Of The Importance Of A Packed Bed Construction Essay

In chemical processing, a packed bed is a hollow tube, pipe, or other vessel that is filled with a packing material. The packing can be randomly filled with small objects like Raschig rings or else it can be a specifically designed structured packing.

1.1 Scope of Work

The purpose of a packed bed is typically to improve contact between two phases in a chemical or similar process. Packed beds can be used in a chemical reactor, a distillation process, or a scrubber, but packed beds have also been used to store heat in chemical plants. In this case, hot gases are allowed to escape through a vessel that is packed with a refractory material until the packing is hot. Air or other cool gas is then fed back to the plant through the hot bed, thereby pre-heating the air or gas feed. (Perry 1984)

In industry, a packed column is a type of packed bed used to perform separation processes, such as absorption, stripping, and distillation. A packed column is a pressure vessel that has a packed section. The column can be filled with random dumped packing or structured packing sections, which are arranged or stacked. In the column, liquids tend to wet the surface of the packing and the vapors pass across this wetted surface, where mass transfer takes place. Packing material can be used instead of trays to improve separation in distillation columns. Packing offers the advantage of a lower pressure drop across the column (when compared to plates or trays), which is beneficial while operating under vacuum. Differently shaped packing materials have different surface areas and void space between the packing. Both of these factors affect packing performance.

Another factor in performance, in addition to the packing shape and surface area, is the liquid and vapor distribution that enters the packed bed. The number of theoretical stages required to make a given separation is calculated using a specific vapor to liquid ratio. If the liquid and vapor are not evenly distributed across the superficial tower area as it enters the packed bed, the liquid to vapor ratio will not be correct and the required separation will not be achieved. The packing will appear to not be working properly. The height equivalent to a theoretical plate (HETP) will be greater than expected. The problem is not the packing itself but the mal-distribution of the fluids entering the packed bed. These columns can contain liquid distributors and redistributors which help to distribute the liquid evenly over a section of packing, increasing the efficiency of the mass transfer. The design of the liquid distributors used to introduce the feed and reflux to a packed bed is critical to making the packing perform at maximum efficiency. (Seader 2006)

Packed columns have a continuous vapor-equilibrium curve, unlike conventional tray distillation in which every tray represents a separate point of vapor-liquid equilibrium. However, when modeling packed columns it is useful to compute a number of theoretical plates to denote the separation efficiency of the packed column with respect to more traditional trays. In design, the number of necessary theoretical equilibrium stages is first determined and then the packing height equivalent to a theoretical equilibrium stage, known as the height equivalent to a theoretical plate (HETP), is also determined. The total packing height required is the number theoretical stages multiplied by the HETP. (Columns 1989)

Columns used in certain types of chromatography consisting of a tube filled with packing material can also be called packed columns and their structure has similarities to packed beds.

Packed bed reactors can be used in chemical reaction. These reactors are tubular and are filled with solid catalyst particles, most often used to catalyze gas reactions. The chemical reaction takes place on the surface of the catalyst. The advantage of using a packed bed reactor is the higher conversion per weight of catalyst than other catalytic reactors. The reaction rate is based on the amount of the solid catalyst rather than the volume of the reactor. (Seader 2006)

Through the project the packed bed absorber will be studies and experiments will be conducted in order to verify the efficiency of the machine in terms of reducing the alcalinity of waste cement water.

The main purpose of the thesis project is to:

To be able to efficiently treat cement factory and construction site water wastes and neutralize cement waste water from a highly basic state, such that its disposal is ecofriendly.

Exploring the fundamentals of acid base titration in order to find out experimental results, absorption rate and concentration of effluents.

To obtain most effective and highest order of mass transfer in the most economical method using simple solutes and substances.

Figure 1: Schematic of a Packed Bed Absorber

1.2 Industrial Application

Packed columns are commonly employed to carry out absorption and scrubbing operations. They provide a medium in which counter-current two-phase flow occurs, and in which a relatively large gas-fluid interface per unit volume of column volume exists. Because of the nature of the packing material (often a ceramic) a packed column can operate using strongly corrosive fluids. Packed columns are often more economical to build and operate than their plate or bubble-cap column counterparts, although pressure drops can be high, which requires larger gas blowers with high energy consumption.

The packed bed absorber in this experiment is to be used eventually to remove ammonia from a waste air stream. Before running ammonia, however, it is necessary to determine what water and air flow rates can be accommodated, to measure the pressure drop across the bed so that the air blower can be specified, and to test a noninvasive method for measuring the amount of water held up on the packing, so that incipient flooding can be detected. (Seader 2006)

An air stream from a drier contains roughly 0.10% by weight (1000 ppm) ammonia. Environmental regulations prohibit discharge of the ammonia into the air, and thus a small packed bed scrubber has been set up to pilot the ammonia removal process. Your job is to run the scrubber at various air flow and water flow rates, and collect data from which can be calculated the height of a transfer unit for the packing used in the scrubber. The results will be passed to a design group which will design a full-scale scrubber, based on the air flow rate from the drier and the maximum allowable ammonia content of the effluent air

1.2.1 Chromatography

Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures. It involves passing a mixture dissolved in a “mobile phase” through a stationary phase, which separates the analyte to be measured from other molecules in the mixture based on differential partitioning between the mobile and stationary phases. Subtle differences in a compound’s partition coefficient result in differential retention on the stationary phase and thus changing the separation. (Laurence M. Harwood 13 June 1989)

Chromatography may be preparative or analytical. The purpose of preparative chromatography is to separate the components of a mixture for further use (and is thus a form of purification). Analytical chromatography is done normally with smaller amounts of material and is for measuring the relative proportions of analytes in a mixture. The two are not mutually exclusive.

1.2.2 Liquid Chromatography

Liquid Chromatography is normally the main area of dealing when involved with the absorption of liquid solution

Liquid chromatography (LC) is a separation technique in which the mobile phase is a liquid. Liquid chromatography can be carried out either in a column or a plane. Present day liquid chromatography that generally utilizes very small packing particles and a relatively high pressure is referred to as high performance liquid chromatography (HPLC). (Rigas n.d.)

In the HPLC technique, the sample is forced through a column that is packed with irregularly or spherically shaped particles, a porous monolithic layer (stationary phase) or a porous membrane by a liquid (mobile phase) at high pressure. HPLC is historically divided into two different sub-classes based on the polarity of the mobile and stationary phases. Methods in which the stationary phase is more polar than the mobile phase (e.g. toluene as the mobile phase, silica as the stationary phase) are termed normal phase liquid chromatography (NPLC) and the opposite (e.g. water-methanol mixture as the mobile phase and C18 = octadecylsilyl as the stationary phase) is termed reversed phase liquid chromatography (RPLC). Ironically the “normal phase” has fewer applications and RPLC is therefore used considerably more. (Laurence M. Harwood 13 June 1989)

Specific techniques which come under this broad heading are listed below. It should also be noted that the following techniques can also be considered fast protein liquid chromatography if no pressure is used to drive the mobile phase through the stationary phase. See also Aqueous Normal Phase Chromatography.

Figure 2: Sophisticated Gas Chromatography System (Source: http://visualsonline.cancer.gov/details.cfm?imageid=2020)

CHAPTER 2: PROJECT DETAILS

There are various forms of construction site wastes which can harm the environment and cause extensive damage to both life and nature. Mainly, as it is well known that water pollution is the main cause of diseases and deaths and more than 14000 people die due to water pollution every single day. It is of utmost importance to at least minimize some forms of water pollution.

2.1 Construction Site Water Wastes

It is common practice in the ready-mixed concrete industry to thoroughly clean the inside of a concrete trucks drum at the end of each day using approximately 150-300 gallons of water. According to the Water Quality Act (part 116), truck wash water is a hazardous substance ( it contains caustic soda and potash) and its disposal is regulated by the Environmental Protection Agency (EPA). In addition, a high pH makes truck wash water hazardous under EPA definition of corrosively. These regulations require accurate and precise record keeping of each waste water disposal, retention of the records for three years, and submission of the records to EPA. The current practices for the disposal of concrete wash water include dumping at the job site, dumping at a landfill, or dumping into a concrete wash water pit at the ready-mix plant. (pHasing Out Unscrupulous Wastewater Disposal 2007).

The availability of landfill sites for the disposal of truck wash water has been drastically reduced for the past ten years. In 198 1, there were approximately 50,000 such sites in the United States; today, there are only about 5,000. In response to this reduction, most ready-mix batch plants have developed a variety of operational configurations to manage their own wash water. The alternatives include settling ponds, storm water detention/retention facilities and water reuse systems. Recognizing that a typical batch plant generate an average of 20 gallons of wash water discharge per cubic yard of ready-mixed production and that the average concrete production rate for a batch plant is 250 cubic yards per day, the proper disposition of the wash water presents an important issue. If this wash water can be reused, it has been estimated that the volume per cubic yard of production that will require special disposal handling can be reduced to 5 gallons. Few research studies have been conducted related to the problem of handling wastes produced in the RMC operations. This paper summaries the information available regarding the handling of waste water in RMC operations. Major issues discussed include, source, quality and quantity of waste water; waste water control systems; suitability of waste water for making concrete; and chemical stabilizing agents.

2.2 Source of Waste Water

The waste water from the RMC operations is usually generated from truck wash systems, washing of central mixing plant, storm water runoff from the ready-mix plant yard, waste water generated from water sprayed dust control and conveyor wash down. The quantity of waste water generated daily vary due to the unpredictable amount generated from storm water runoff. However, it has been estimated that when a 10 cubic yard ready-mix truck delivers concrete, 1 to 4 percent or approximately 600 lb of concrete adhere to the inside of the drum and mixing blades. At the end of the workday, the ready-mix truck has to be cleaned of all the residue concrete. Removing the residual cementations material adhering to the drum and blades of a single truck unit can require approximately 150 to 300 gallons of water. (Mbwambo 1996)

2.3 Quality of Waste Water

The quality of waste water from the RMC operations is derived from the source of the water itself. Wash water discharge from truck wash contains cementitious materials and chemical admixture residue. Storm water runoff may also contain cementitious materials and other impurities washed from the plant yard. Due to the high content of dissolved limestone solids the wash water is caustic and has a high pH value ranging between 11 and 12. In general the waste water contains dissolved solids which include: sulfates and hydroxides from cement, chlorides from the use of calcium chloride as an admixture, oil and grease from the equipment, and small quantities of other chemicals associated with hydration of Portland Cement and derivatives from chemical admixtures [3]. The most common derivatives of chemical admixtures are: ethanolamine, diethanolamine, formaldehyde, K-naphthalene sulfonate, and benzene sulfonic acid. (Mbwambo 1996)

2.4 The pH Problem

The pH of concrete wash water is incredibly high – typically 12 to 13.5 on a scale which runs from zero (very acidic) to 14 (highly alkaline). The water is extremely corrosive, highly toxic to fish and other aquatic wildlife and, with prolonged skin contact, capable of causing second degree burns. The only commonly-used commodity with a higher pH is domestic oven cleaner. Therefore, high pH water’s potential to cause environmental harm is often overlooked or misunderstood.

Figure 3 A Cement Ready Mix Truck (pHasing Out Unscrupulous Wastewater Disposal 2007)

A recent Environmental Audit on a large commercial building project revealed that washing truck mixer discharge chutes alone generates about 20 liters of high pH wash-water and up to five liters of waste concrete per truck. Over the entire construction phase of the project this amounted to 75m3 of potentially environmentally-damaging wash-water. Yet dilution is definitely not the solution to pollution from concrete wash-water. Unfortunately, pH is a logarithmic scale and so the release of even a small quantity of concrete wash-water can significantly increase the pH of a receiving watercourse. (pHasing Out Unscrupulous Wastewater Disposal 2007)

For example, the release of 75m3 of pH 13 wash-water would theoretically raise the pH of 750,000m3 of neutral river water to pH 9 – the limit commonly adopted for discharge to the environment.

This is equivalent to polluting 300 Olympic-sized swimming pools. Consequently, the uncontrolled release of even a small quantity of high pH wash-water can have a devastating effect on the environment.

2.5 Possible Solution

The proposal of this project prospects the introduction of the packed bed reactor in the process of waste water treatment. It is well known that the pH level of the waste water shows that the liquid is highly basic and this water if reacted with gasses will absorb in order to turn neutral up to a limit that it can be safely disposed of. The scope of this project will deal with the absorption of these basic fluids with CO2 gas which will help convert the liquid from basic to neutral.

CHAPTER 3: TESTING OF WASTE WATER

Titration is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of a known reactant. Because volume measurements play a key role in titration, it is also known as volumetric analysis.

3.1 Titration

A reagent, called the titrant or titrator, of a known concentration (a standard solution) and volume is used to react with a solution of the analyte or titrand, whose concentration is not known. Using a calibrated burette or chemistry pipetting syringe to add the titrant, it is possible to determine the exact amount that has been consumed when the endpoint is reached. The endpoint is the point at which the titration is complete, as determined by an indicator (see below). This is ideally the same volume as the equivalence point-the volume of added titrant at which the number of moles of titrant is equal to the number of moles of analyte, or some multiple thereof (as in polyprotic acids). In the classic strong acid-strong base titration, the endpoint of a titration is the point at which the pH of the reactant is just about equal to 7, and often when the solution takes on a persisting solid color as in the pink of phenolphthalein indicator (Rosenfeld 1999)

3.2 Procedure

A typical titration begins with a beaker or Erlenmeyer flask containing a precise volume of the reactant and a small amount of indicator, placed underneath a burette or buretting syringe containing the reagent. By controlling the amount of reagent added to the reactant, it is possible to detect the point at which the indicator changes color. As long as the indicator has been chosen correctly, this should also be the point where the reactant and reagent neutralize each other, and, by reading the scale on the burette, the volume of reagent can be measured.

As the concentration of the reagent is known, the number of moles of reagent can be calculated (since Molarity = number of moles / volume (L). Then, from the chemical equation involving the two substances, the number of moles present in the reactant can be found. Finally, by dividing the number of moles of reactant by its volume, the concentration is calculated. (Rosenfeld 1999)

Indicator

Color on Acidic Side

Range of Color Change

Color on Basic Side

Methyl Violet

Yellow

0.0 – 1.6

Violet

Bromophenol Blue

Yellow

3.0 – 4.6

Blue

Methyl Orange

Red

3.1 – 4.4

Yellow

Methyl Red

Red

4.4 – 6.2

Yellow

Litmus

Red

5.0 – 8.0

Blue

Bromothymol Blue

Yellow

6.0 – 7.6

Blue

Phenolphthalein

Colorless

8.3 – 10.0

Pink

Alizarin Yellow

Yellow

10.1 – 12.0

Red

Table 1: Data on Indicators

CHAPTER 4: LITERATURE SURVEY

Structured packing’s were developed in early 1960s, and in the 1970s they came into wide use in various separation processes as contact devices of industrial columnar apparatuses for implementing heat and mass exchange processes, such as absorption, fractionation, extraction, purification and drying of gas, etc.

We propose to define structured packing’s as regular packing’s that are comprised of packets assembled from flat or corrugated sheets forming a spatial multichannel structure. Sheet packing components made of metal foil, network, and polymer, ceramic and other materials may lie in the apparatus as a pack of sheets, may be twisted into spirals and cylinders, and assembled into honeycombed or cellular structures. Coaxial channels thus formed, depending on the shape and relative dispositions of individual sheets; have various configurations ranging from simple (round or polygonal cross section) to complex spatial packing periodically changing with height. Thus, the proposed term “structured packing’s” encompasses a whole multitude of film-type heat-exchanging contact devices (for instance, sprinklers) for cooling towers.

4.0 Introduction on Packing Materials:

Most popular in the industry are structured packing’s of the type that are well adaptable to process conditions and geometric dimensions of the apparatuses. Such packing’s are distinguished by equally high and stable indices of separation of the components of mixtures in a wide range of diameters of the mass-exchange columns (80 mm-20 m). They are usable in almost all process conditions regardless of pressure in the apparatus, gas flow velocity, and liquid load per unit cross sectional area of the apparatus. (D.K. 1980)

Various packing heights of the absorber component were tested to determine the optimal performance of the combined unit. And the various research areas include.

Improved understanding of physical phenomena of the packed bed column.

Better sampling of output mass transfer values

Analytical and flow-visualization methods.

Better predictive modelling.

The Packing of the packed bed column must be selected on various parameters, specially to suit the requirements and the application of the packed bed column. Even though the main objectives of any packing is to maximize the efficiency of mass transfer which can be attained in the following ways:

To maximize the specific surface area

To spread surface area uniformly.

To promote uniform distribution of vapor & liquid throughout the bed

To freely drain any liquid so that stagnant liquid pockets are minimized

To maximize the wetting of packing surface

To maximize the void space per unit column volume.

To minimize friction (good Aerodynamic characteristics).

To ensure uniform resistance to vapour & liquid flow throughout the bed.

To permit easy disengagement of vapour from liquid.

To maximize resistance to mechanical deformation under the weight of bed.

To minimize cost.

To maximize the fouling resistance.

To minimize the liquid holdup.

To minimize damage during abnormal operation.

4.1 Types of Random Packing:

There are various types of random packing materials available in the market with specialized industries dealing with the manufacture of these packing materials. With the growing demand technology in the designing of packing materials has also advanced with generations of packing materials such as:

First generation packing (Raschig rings, Lessing Rings, Berl saddles)

Second generation packing(intalox saddles, pall rings, Hy-pak )

Third generation packing(CMR, Chempak, Nutter rings, Hckp, fleximax, hiflow rings, Lanpac, Impac etc)

Other miscellaneous random packing (Dinapac, super Torus VSP, Interpack, Tellerette, maspac, Levapac etc) (C.G. 1989)

4.2 Rasching Rings:

Raschig rings are pieces of tube (approximately equal in length and diameter) used in large numbers as a packed bed within columns for distillations and other chemical engineering processes. They are usually ceramic or metal and provide a large surface area within the volume of the column for interaction between liquid and gas or vapour. Raschig rings made from borosilicate glass are sometimes employed in the handling of nuclear materials, where they are used inside vessels and tanks containing solutions of fissile material, for example solutions of enriched uranyl nitrate, acting as neutron absorbers and preventing a potential criticality accident. [1]

Specifications:

First generation random packing.

made from metals like carbon steel or very high alloys such as Monel 400 or Hastelloy C276.

Special Carbon or Graphite made are used in specific applications

Resistant to most acids, alkalis and solvents at temperatures as high as 1500C

Good erosion and thermal shock resistance.

Figure 4: Raschig Rings (CARBON PRODUCTS (INDIA) 2006)

4.3 Pall Rings

Second-generation, random packing.

Primarily made of 304SS and 316L SS metal alloys for quick replacement in kind from stock materials.

Carbon Steel and specialty alloys, such as Monel 400 and Hastelloy C276, made are used for specific applications

Pall Rings are available in various sizes such as (mm) 16, 25, 38, and 50.

Figure 5: Pall Rings (CARBON PRODUCTS (INDIA) 2006)

4.4 Saddle Rings

Saddle Rings were originally introduced to the industry under the product name IMTP® Intalox Metal Tower Packing, a registered trademark of Koch-Glitsch, LP. In terms of performance they are:

In terms of performance, i.e., low-pressure drop and high efficiency.

Used in both high pressure as well as vacuum towers.

Large effective interfacial area,

High mechanical strength

And lower cost due to less metal than previous generations of random packing. (D.K. 1980)

Available in various sizes, which give different combinations of efficiency and pressure drop

Figure 6: Saddle Rings (CARBON PRODUCTS (INDIA) 2006)

4.5 High Performance Random Packing

The random packing with high performance have high void fraction & well distributed surface area which increases the efficiency. They also have a more open shape which improves liquid spreading, low pressure drop and high capacity with high specific heat transfer coefficient. The main specifications of these high performance random packing are:

High strength to weight ratio.

High vapor capacity and low pressure drop

High efficiency

High liquid handling capacity

Fouling resistant

Open side facing vapor flow, reduces friction.

High capacity and low pressure drop

High efficiency

Fouling resistant

Figure 7: High Performance Random Packing’s (CARBON PRODUCTS (INDIA) 2006)

4.6 Nutter Ring

Nutter rings were mainly developed for efficiency enhanced by lateral liquid spreading and surface film renewal along with superior surface utilization in mass and heat transfer, allowing shorter packed bed heights. It is also a high performance random packing verified by tests conducted at Fractionation Research Institute which provides mechanical structure with maximum randomness with minimal nesting. (Random Packing n.d.)

4.7 Katapakâ„¢-SP Specifications:

Corrugated sheet spreads in a series of parallel planes.

Packing for reactive distillation and trickle-bed reactors

High separation efficiency and high reaction capacity

Figure 8: Katapakâ„¢-SP (CARBON PRODUCTS (INDIA) 2006)

4.8 Mellapakâ„¢

Universal packing type with surface area of 250m2 /m3

Suitable for a wide range of applications for low to very high liquid loads/ vacuum to gauge pressure.

Available made of wide pallet of stainless steel, alloys and thermoplastics

Figure 9: Mellapakâ„¢ (CARBON PRODUCTS (INDIA) 2006)

4.9 Borosilicate Glass Raschig Rings:

Borosilicate glass is a type of glass with the main glass-forming constituents silica and boron oxide. Borosilicate glasses are known for having very low coefficients of thermal expansion (~5 Ã- 10âˆ’6 /°C at 20°C), making them resistant to thermal shock, more so than any other common glass. Such glass is less subject to thermal stress and is commonly used for the construction of reagent bottles. (D.K.Fedrich 1980)

Raschig rings used as a safety mechanism, to avoid critical reactions in solutions containing radioactive materials, are usually made of borosilicate glass. Since boron is the active neutron absorbing ingredient, it is important to determine the boron content in the Raschig rings at any given time. A method has been developed to determine rapidly the boron content of borosilicate glasses. Ion exchange and potentiometric measurement are used to determine boron as the tetrafluoroborate ion. The precision of the method is ±2.0 mV. The average difference between values of a wet chemical analysis and those of the potentiometric method is 7.7%.

4.10 Comparison of Structured packing against Random:

The comparison is made for the following crieteria:

Specific surface area vs. packing factor

HETP vs. sp. Surface area

Liquid holdup vs. liquid flow rate

Figure 10: Specific surface area vs. packing factor (Sung Yong Cho n.d.)

Pressure drop per theoretical stage

Figure 11: Specific surface area vs. packing factor

Figure 12: HETP vs. Sp. Surface Area (Sung Yong Cho n.d.)

Figure 13: Pressure Drop Per Theoretical Stage (Sung Yong Cho n.d.)

Figure 14: Liquid Holdup Vs. Liquid Flow Rate (Sung Yong Cho n.d.)

4.11 Use of Packed Bed Absorber

The packed bed absorber is the perfect device that can be used for the treating of the waste cement water. The solute can be run through the packing while the CO2 gas can help in the absorption and neutralization process. The literature survey will consist of an elaborate study of four different types of structured packing and their performances which can be used in this process.

Gempak-4A

Mellapak 500Y

Mellapak 500X

Optiflow

4.11.1 Gempak-4A

The Gempak 2AT packings of the German company Glitsch consist of vertically oriented thin metal plates whose disposition creates a labyrinth for vapor-liquid contact and improve mixing. Even flows of the liquid film run down these plates and come in contact with their opposite sides, and the vaporous flow moves upward between the plates without obstruction. Unique topography of the packing surface facilitates mixing of the liquid films on both sides of the plates. The vapor and liquid mix uniformly throughout the cross section of the column on account of 90° turn of the Gempak packing packets arranged sequentially across the column height. Besides high efficiency, Gempak packing ensures lower pressure differential, greater power, and longer service life compared to the preceding packing’s. (Dmitrieva 2005)

4.11.2 Mellapak

The MELLAPAK packing consists of structure-forming elements, which fill the entire section of the column. Neighboring elements are oriented at an angle of 90 ~ with respect to one another. Each element consists of parallel folded corrugated metallic sheets. The corrugations are applied at a fixed angle ff to the vertical axis, and are directed toward the opposite sides of the column on adjacent sheets. The area of the specific geometric surface a i of the packing can be varied over a broad range by varying the geometric characteristics of the corrugation. Of the 12 different types of MELLAPAK packings currently produced, four types (MELLAPAK I25.Y, 250.Y, 350.Y, and 500.Y) will be described in detail. The conventional notation of the type of packing includes two geometric indicators: Y represents the value of the angle ff = 45 ~ and the number the specific geometric surface of the packing in m2/m 3 (thus, a i = 250 m2/m 3 in the case of the MELLAPAK 250.Y packing). (Meier 1994)

Figure 15 Mellapack 500Y

4.11.2.1 Performance of Mellapak

The performance characteristics of the four types of MELLAPAK packings (125.Y-500.Y) were determined in an experimental column with an internal diameter of 1 m on test machines manufactured by the “Zultzer” Compa W in Winterthur. This column and the method of investigation were conducted in the complete-reflux-recovery mode. The pressure in the upper part of the column was 10-960 mbar (1-96 kPa). Trans-/cis-decalin and chlorine-/ethyl benzene in conformity with familiar recommendations [2] served as test mixtures. The height of the packing was varied from 1.4 to 8.5 m. Approximately 200 experiments, the results of some of which are presented below, were conducted. Curves of the efficiency (NTPM) and pressure differential (Ap/Az) versus the vapor load for four types of packings under a pressure of 25, 100, and 960 mbar (2.5, 10, and 96 kPa) in the upper portion of the column are presented in Fig. 3. Experimental points presented were obtained for a pressure of 100 and 960 mbar (10 and 96 kPa) in the upper portion for a chtorine–/ethyl benzene mixture. The vapor loading is determined by the F-factor where Wg is the vapor velocity reduced to the column section in m/sec, and pg is the vapor density in kg/m 3. (Meier 1994)

CHAPTER 5: EXPERIMENTATION CONDUCTED

The following chapter will depict the summary of all the experimentation conducted within the laboratory premises on the various needed chemicals and specially the cement water in concern.

5.1 Test Titrations

Making 2N (aq) NaOH solution by dissolving 800gms of NaOH in 10ltr’s of water

2N NaOH = 100ml

N= gm eq. wt / Liter

Gm eq wt = 40gm/1l = 1N

Preparation of 1N of Hcl ie. 500ml Hcl of 1N

Preparation of saturated Bacl2 solution – 250ml

Hcl – 18.5gm – 45.5gm – 1l – 1N

5.1.1 Indicator Values

Phenolphthalein: Base – Pink

Acid – Colorless

Methyl orange: Base – yellow

Acid – Orange

5.2 Observation In Test Absorption Unit

Flow rate of NaOH in m3 /sec = (fn/3600*1000)

= 5/(3600*1000)

= 1.38 * 10-6 m3/sec

Flow rate of CO2 = 5 * 10-5 m3/sec

Flow rate of air = 6.66 * 10-4 m3/sec

Concentration of NaOH at outlet = .28gmol/L

Absorbed CO2 = -1.242 * 10-7 gmol-m3/L

Molar volume = 22.45 L/gmol

Volume of absorbed CO2 = -27.88 * 10-7 m3

Flow rate of CO2 at outlet = 5.2788 * 10*5 m3/sec

Partial pressure of CO2 at the outlet = 0.0734

Log mean pressure = 0.3547

Gas Phase mass – transfer coefficient = -2.9727 * 10-4

Volume of column = 1.178 * 10-3 m3

5.3 Experimentation on Alkaline Cement Waste Water

The experimentation was conducted on various samples of waste cement water with known concentration of cement and alkalinity. During the experimentation samples of 10gm, 20gm, 30gm cement dissolved in water were taken to check for differences in pH level. The observation stated the following:

Serial no

Cement in gm.

Water in ml

pH Level

12.36 -12.40

12.35

12.32

Table 2: Observation Table 1

From the next following observation table which consists of cement samples of 2gm, 4gm, 6gm and 8gm it will be seen that the alkalinity of the solution rises steeply but while the cement concentration increases the rise in pH reduces. Thus, proving that the amount of cement contamination in the water doesn’t matter and treatment of the waste water must be done even if the concentration of cement in the water is low.

Serial no

Cement in gm.

Water in ml

pH Level

11.66

11.79

11.83

Table 3: Observation Table 2

It can be clearly seen in the above table that in values of 6gm cement and 8gm cement that pH level remains constant.

Figure 16: pH Indicator MachineThese values were compared with the alkalinity of 1N NaOH solution which resulted with a pH of 12.79, thus showing that waste cement water can be almost as alkaline as NaOH solution. Further, the 10 gm. Cement in water solution was reacted with CO2 gas in order to conduct the absorbing experiment. The solution after treatment was tested under titration methods which showed color change to yellow and displayed pH level as 7.90 thus making the highly alkaline solution almost neutral. The titration was done with the help of 1N Hcl which is a strong acid with pH 0.93.

5.4 Experimentation and Observations on Waste Cement Water

A 0.001 N of Hcl was prepared for the titration process .Decanted cement water, was collected and passed through the packed bed absorber.

CO2 was passed through this solution.

A 10 ml sample of the reacted the waste cement water was obtained at regular intervals varying different parameters and titrated with 0.001 N Hcl with phenolphthalein and methyl orange as indicators .

Values for flow rates of cement waste water, CO2 and air were further calculated.

Hcl run down during titration were noted down.

Further using these parameters amount of absorbed CO2 was found out.

Further molar volume, volume of absorbed CO2, flow rate of CO2 at outlet and partial pressure of CO2 were derived.

These variables were used to find out the log mean pressure, and the final mass transfer coefficient.

Thirty Six observations were conducted with the reacted waste cement water by varying the parameters of flow rate of the waste cement water, air and carbon dioxide.

Further on the values of mass transfer co-efficient were calculated and recorded in the following observation table.

SERIAL

VHCl2

KGa

2.6

2.88E-06

2.8

2.85E-06

3.2

2.81E-06

0.5

3.7

2.75E-06

3.5

2.77E-06

2.71E-06

4.5

2.65E-06

0.5

2.59E-06

2.83E-06

3.4

2.78E-06

5.2

2.57E-06

0.5

6.7

2.39E-06

2.9

4.26E-06

3.1

4.23E-06

3.8

4.1E-06

0.5

4.07E-06

4.1

4.05E-06

4.7

3.94E-06

5.2

3.85E-06

0.5

6.1

3.7E-06

4.9

3.91E-06

5.1

3.87E-06

6.4

3.64E-06

0.5

7.3

3.48E-06

3.3

5.59E-06

3.5

5.54E-06

4.3

5.35E-06

0.5

4.5

5.3E-06

4.6

5.28E-06

5.2

5.14E-06

5.7

5.02E-06

0.5

6.9

4.74E-06

5.4

5.09E-06

5.7

5.02E-06

7.1

4.69E-06

0.5

7.7

4.55E-06

Table 4: Observation Table for Conducted Experimentation

From the values in the observation table graphs were plotted in order to find out a trend line. The reason this was done is to be able to find out the variations in mass transfer efficiency keeping in mind only specific parameter such as flow rate of cement water or flow rate of carbon dioxide or the flow rate of air against the values of KGa.

Graph 1: Flow Rate of Cement Water VS KGa

Graph 2: Flow Rate CO2 VS KGa

Graph 3: Flow Rate Air VS KGa

5.5 Anova Study:

A single factor anova study was conducted on the above shows observation table in order to verify the parameter that most highly influences the efficiency of mass transfer. The anova study results are as follows:

Anova: Single Factor

SUMMARY

Groups

Count

Sum

Average

Variance

Column 1

540

17.143

Column 2

58.5

1.625

0.9482

Column 3

1080

68.571

Column 4

0.0001

4E-06

1E-12

ANOVA

Source of Variation

P-value

F crit

Between Groups

21030

7010

323.55

9.69785E-63

2.6693

Within Groups

3033.2

140

21.666

Total

24063

143

5.6 Feasibility Study

The experimentation conducted as of now has proven that the project promises a wide range of avenue in the field of waste water treatment. The cement waste water can be treated efficiently and effectively by the methods of absorption and with the help of a packed bed column.

5.7 Future Work

The initial stages of the experimentation have just begun; this experimentation will be conducted keeping in minds the following aspects.

In order to analyze the performance of four different types of packing materials for the test column. The packing materials will be experimented upon with keeping in mind various parameters such as flow rate of CO2, flow rate of alkaline solution (waste cement water). These parameters will me alternatively varied to arrive at the highest possible mass transfer value.

It will be observed in the further scope of study that where different samples of cement contaminated waste water will be used. These samples will also be tested on with the help of different types of structured packing materials in order to gain better insight on the efficiency of the absorption by recording the rate of mass-transfer and the pH of the post reacted cement waste water.

These samples will be then tested according to the allowed pH levels for disposal of waste water. The most efficient and least time consuming and the best structure will be sated as the conditions for optimum treatment of the cement waste water.

Chapter 6: Results and Discussion

It is observed that such techniques can be employed to neutralize the waste cement water which is highly basic in nature and at the same time CO2 emitted by factories can be utilized for this process of absorption instead of letting it into the atmosphere. These techniques are also useful in the purification of the cement factory wastes. The waste water can be checked for pH levels and further put through the process of absorption in which the pH level of the waste water can be neutralized to a allowed limit Liquid flow rates and CO2 flow rates have significant impact on the efficiency of the packed bed absorber. Rise in these parameters normally increases the mass transfer efficiency. Variating the type of packing material also effects the efficiency. Borosilicate glass raschig rings having the ability to be best suited for this process. Liquid distribution also being an important parameter effects the mass transfer efficiency.

CHAPTER 6: CONCLUSION

It can be stated that the experimentation conducted as of now display positive results in the process of neutralizing the alkaline solutions. The area of major concern, in the waste cement water, being the control of pH level which can be efficiently treated with the help of the packed bed reactor and simple economical reactants. The CO2 gas can be obtained also from the waste of large industries which some-times let these harmful gasses into the atmosphere. It is also known that excess of CO2 in the atmosphere can cause ozone damage this driving the greenhouse effect which is also a topic of major concern to environmentalists. These gasses can be effectively recycled and used to also treat the cement water wastes which also will help in the emancipation of the environment. The scope of the project further proposes the analysis of various packing materials used in the packed bed reactors. These packing materials will be used in elaborate lab experimentation in order to derive the outputs of each. Titration will be one of the most utilized experimentation methods to rank the efficiency of each of these packing materials. The scope of the project will help developing a newer and efficient method of treating the effluents and controlling the pH level of waste water which is normally dumped into the already damaged environment.

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