Deposit is the procedure of dividing a liquid mixture of suspended atoms into clear supernatant liquid and denser slurry holding a higher concentration of solids. This is normally accomplished by leting the atoms to settle through the force of gravitation. automatically utilizing centrifugal force. or electrostatically utilizing an electric current. Continuous deposit armored combat vehicles are normally used in effluent intervention installations to divide suspended atoms from effluent.
This experiment aims to find the consequence of initial concentration and initial tallness of the slurry on its subsiding features. Using a set of informations obtained from the experiment. a uninterrupted thickening or clarifier must so be designed. The batch deposit experiment was accomplished by mensurating the tallness of the clear liquid interface at two-minute intervals utilizing initial concentrations of 25. 50. and 75 gms per litre and initial volumes ( exchangeable to height ) of 1000. 900. and 800 millilitres. Two tests were conducted for each matrix.
From the information. it was observed that as the initial concentration of slurry is increased. the initial subsiding speeds lessening. The initial tallness has no consequence on the initial subsiding speed but can impact the rate at which solids compact. However. it was found that how the tallness affects compression can be unpredictable. For the design of a thickening utilizing batch deposit informations. the needed country was calculated utilizing the Coe and Clevenger. and the Talmadge and Fitch methods. The consequences were 1. 3112 M2 and 2. 2714 M2. severally.
During the class of the experiment. assorted jobs were encountered that may hold lead to little mistakes. These jobs were normally jobs of measuring. Using dissembling tape can do little mistakes if non applied to the cylinder decently. There were little troubles during the initial stirring of the slurry because of the deficiency of long stirring rods. Furthermore. consequences from the informations gathered were somewhat erroneous as the aforesaid methods rely to a great extent on graphical attacks of calculation.
Deposit is the separation of a suspension into a supernatant clear fluid and dense slurry which contains a higher concentration of solid. This procedure describes the gesture of atoms in suspensions or molecules in solutions in response to external forces such as gravitation. centrifugal force. or electric force. This besides pertains to objects of assorted sizes. runing from suspensions of dust and pollen atoms to cellular suspensions to solutions of individual molecules such as proteins and peptides.
Deposit may be divided into the functional operations of thickener and elucidation. The chief intent of inspissating is to increase the concentration of suspended solids in a provender watercourse. while that of elucidation is to take a comparatively little measure of suspended atoms and bring forth a clear wastewater. These two maps are similar and occur at the same time. and the nomenclature simply makes a differentiation between the primary procedure consequences desired. In general. thickening mechanisms are designed for the heavier-duty demands imposed by a big measure of comparatively concentrated mush. while clarifiers normally will include characteristics that guarantee basically complete suspended – solids remotion. such as greater deepness. particular proviso for curdling or flocculation of the provender suspension. and greater overflow-weir length.
Commercial deposit of H2O suspensions is conducted as a uninterrupted procedure in thickenings or big armored combat vehicles which receive the suspension or dilute slurry at the centre or side. allow the flood of supernatant liquid. and produce sludge from the underside of the armored combat vehicle.
Sedimentation basically proceeds harmonizing to the strategy shown below.
At the beginning of the operation. the suspended solids fall through the liquid under hindered subsiding conditions. Finally. assorted zones signifier. Zone A is the supernatant liquid. The interface between A and B is distinguishable merely when the atoms in B are closely sized with regard to the smallest atoms. Otherwise. a milklike interface is formed. B is a suspended mixture of solids and liquid and has unvarying concentration. Between B and C is a distinguishable passage zone. This zone is due to the lifting liquid as the extremely concentrated sludge D compacts. Zone c. unlike B. is a part of variable concentration. Note that regions A and D turn larger at the disbursal of B and C until such a point where maximal compression of D is obtained. This point is called the critical subsiding point. At his point. merely a individual. distinguishable interface is formed between the concentrated sludge and the clear liquid.
To find the consequence of concentration or tallness on the settling features of a suspension. batch deposit experiments are conducted. The information from these experiments can be used to plan a uninterrupted thickening.
Continuous thickenings consist of zones similar to a batch deposit procedure except that these zones are of changeless tallness when steady province is achieved. The design of these thickenings s based on the designation of the concentration of the rate restricting bed.
First. batch settling informations is obtained by plotting the tallness of the interface ( between the clear liquid and slurry ) . z versus clip. Please refer to the figure below. This uses the Talmadge and Fitch method.
A tangent line is drawn at the beginning ( line B ) and at the terminal ( line D ) . The parts from which these tangent lines are drawn represent parts during the trial where subsiding speeds are about changeless. An angle bisector line is so drawn. The intersection between this line and the curve represents Cc from which one can gauge the technetium and Zc. These are the critical status. clip. and height severally. By stipulating the initial tallness. Zo. initial concentration. Co. and underflow concentration. Cu. on can find the ultimate tallness Zu. utilizing the undermentioned equation:
Zu = ZoCo
A tangent line ( line E ) is so drawn. Using the value for Zu. tu is so estimated.
The design applied scientist normally specifies the provender flow rate. Lo. By utilizing the undermentioned equation. the country of the unit can so be calculated:
A= Lo tu
Another method used to find the thickening country is a method devised by Coe and Clevenger. Their on the job equation is
coZo = cLZi
where carbon monoxide = initial slurry concentration
Zo= initial tallness
cL= concentration of solids when the slurry is of height Zi.
Using batch-settling trial informations. a secret plan of interface tallness as a map of clip is made. Because initial concentration and tallness is easy known or measured. one can find CL at height Zi corresponding to a peculiar blink of an eye of clip. T.
The on the job equation is therefore rearranged as follows:
chlorine = coZo
To find Zi at a peculiar clip t1. a tangent line is first drawn at a point of the curve at that place t=t1. Please see the figure below.
The tallness Zi is the y-intercept of the tangent line.
The subsiding speed at a peculiar clip. t1. is the incline of the curve at that blink of an eye. Therefore. V = dz/dt. Simply put. the speed is equal to the incline of the tangent line.
To find the thickening country. one must first compute for the entire flux of the subsiding belongingss. This is the amount of the batch flux and the flux related to the remotion of solids due to the remotion of solids due to the underflow. Mathematically.
F = Fb + Fu
where Fb= cLV and Fu= cLVu. Note that Vu is the underflow speed and is normally randomly chosen by the design applied scientist based on a figure of conditions. The values for Fb. Fu and F at different cases of clip are normally listed on a tabular array which typically arranged like so
t. hour or mins
V. cm/hr or cm/mins
. Fu. g/cm2hr
Fb1 + Fu1
A secret plan of F as a map of concentration is so made. The lowest point of the secret plan of F is taken as FL. This value is so used in the equation.
A= Lo Co
to find the country. A. Lo in this instance is the provender rate and is specified by the design applied scientist.
MATERIALS AND METHODOLOGY
Six ( 6 ) 1000 milliliter graduated cylinders
Calcium carbonate ( CaCO3 )
top burden balance
tap H2O as the dissolver
Consequence of Initial Concentration
Samples of Ca carbonate weighing 25. 50. and 75 gms were weighed utilizing a top burden balance. Each sample was so placed in a 1000 milliliter graduated cylinder and was filled utilizing pat H2O up to the 1000 milliliter grade. The solutions were assorted exhaustively utilizing a stirring rod until unvarying distribution of the solids was observed. The initial highs of the mixtures were instantly recorded after stirring. Clear liquid interface highs were measured at every two minute interval following the first measuring. Measurement continued until no important alteration in tallness was observed. Two tests were conducted.
Consequence of Initial Height
Samples weighing 20. 22. 5. and 25 gms were weighed utilizing a top burden balance. Each sample was so placed in a 1000 milliliter graduated cylinder and was filled utilizing pat H2O up to the 800. 900. and 1000 milliliter Markss so that the mixtures have unvarying concentrations of 25 g/L. The solutions were exhaustively assorted utilizing a stirring rod until unvarying distribution of the solids was observed. The initial highs were recorded instantly after stirring. At two minute intervals thenceforth. the highs of the clear liquid interface were measured. Readings continued until no important alterations in the tallness were observed. Two tests were made.
RESULTS AND DISCUSSION
The first aim of this exercising was to find the consequence of the initial concentration ( carbon monoxide ) of a slurry on its subsiding features. This was accomplished by mensurating the tallness of the clear liquid interface ( at two-minute intervals ) of slurries holding assorted concentrations of 25. 50. and 75 g/L. The information collected ( tallness as a map of clip ) shall hereinafter be referred to as _batch deposit data_ . To depict the settling features of the slurry. the informations obtained were treated utilizing the method proposed by Coe and Clevenger ( Foust. 1980 ) in which tangent lines are drawn at arbitrary points along the secret plan. The incline of a tangent line is equal to the settling speed of the solids at that peculiar arbitrary point.
The informations obtained were so processed and a careful examination of which revealed that a higher concentration by and large causes a lessening in the overall subsiding speed of the solids. This tendency is illustrated in a secret plan of speed versus clip in the undermentioned figure. Please mention to this figure in the treatment to follow.
FIGURE 3. 1. Settling VELOCITY VERSUS TIME PLOT USED TO ILLUSTRATE THE EFFECT OF INITIAL CONCENTRATION ( TRIAL 1 ) .
It is apparent in the graph that slurries with lower concentrations have higher subsiding speeds. It was discussed in the introductory subdivision that as batch deposit begins. the atoms fall at their terminus ( or upper limit ) speeds at hindered-settling conditions. At higher concentrations. more solid atoms are present per arbitrary bed of a peculiar volume. It hence follows that at these conditions. the rate at which particle A settees is lower because of the closer distance between it and particle B. C. D. and so on. This is because the other atoms hinder atom Angstrom from falling. This can be likened to a traffic jam. The greater the figure of autos per strip of route. the slower they run.
Notice the sudden slope in the secret plan. This sudden lessening in settling speed is more outstanding at lower concentrations. Harmonizing to Brown ( 1973 ) . this is due to the diminishing suspended-solids zone ( or zone B in the _Principles_ subdivision ) . It is at this point where the clear liquid interface approaches the solid-liquid interface. As they approach. zone B increases in fluid viscousness and denseness. This causes a crisp lessening in settling speed for lower concentrations and a more shallow lessening for higher concentrations.
The lower portion of the secret plan represents the stage at which the solids enter compression. This is characterized by a really slow procedure of solid buildup which may be correspondent to a fluid fluxing through a bed of diminishing porousness ( Brown. 1973 ) . As the solids compact. the atoms occupy nothingnesss within the interstices of the packing bed. This causes an equal volume of liquid to flux upwards and into the variable concentration zone. This causes a steady lessening in the subsiding speed. Note that at higher concentrations. compression occurs at a faster rate. Although the literature is unequal refering this phenomenon. it is by and large believed that the increased subsiding rate is due to the heavier packing layer nowadays at higher concentrations.
Note besides that the aforesaid observations were the cardinal premises used by Coe and Clevenger. They assumed that deposit rates are a map of local concentration. It is found that the information conforms to their premises and clearly supports them. Below are secret plans of the clear liquid interface tallness as maps of clip. Notice that at higher concentrations. the incline during the initial subsiding period is lower. Because the incline is equal to the subsiding speed. a lower incline indicates a lower rate of settling. These graphs clearly show the velocity’s dependance on slurry concentration.
To explicate the consequence of initial tallness on the settling features of a slurry. delight refer to the undermentioned secret plans.
Consequences of the consequence of changing initial tallness with changeless concentration can be generated from these figures. Brown et Al. ( 1973 ) stated that the changeless rate of deposit at the beginning is the same and independent of the tallness. Apparently. consequences from test 1 and test 2 clearly support this statement. At the start of deposit. all atoms begin to settle and are assumed to quickly near their terminal speeds under hindered-settling conditions ( Foust et al. ) Particle subsiding can be categorized into two types: free-settling and hindered subsiding. The former pertains to the atoms at low concentration that are sufficiently far apart to settle freely while the latter refers to the atoms that are close together that they continuously collide such that their gesture is impeded by other atoms.
For test 1 and test 2 of the experiment. the tallness of the clear liquid interface can be described as invariably diminishing until about five proceedingss of settling clip. From the get downing up to the estimated five minute-settling clip. the graphs generated seem to be a consecutive line for both tests. The inclines of these graphs. holding clip as the independent variable and height as the dependant variable. are about equal with regard to the given concentrations. Therefore. the atoms are sing a changeless subsiding rate. It has besides been observed that during these times in the experiment. settling rate is independent of the tallness. That is. the initial subsiding speeds of the atoms are unaffected by the initial tallness of the slurry.
However. after the estimated five minute-settling clip. the graphs seem to alter their way independent to each other. The calibrated cylinder with a 20g/800mL sample reached hindered-settling foremost for both tests while the sample that has a 25g/L reached last. During the hindered-settling period. atoms are being affected by other atoms more than it has experienced during the free-settling period. Finally. the graph approaches an about consecutive horizontal line. This horizontal line. harmonizing to literature. is the ultimate tallness.
Ultimate tallness is merely the concluding tallness of the solids when settling Michigans. Therefore. settling rate after free-settling is now dependent on the initial tallness. The lower the initial tallness. the faster it can make the hindered-settling government and the ultimate tallness. This phenomenon can be attributed to the fact that solids at a lower slurry deepness have a shorter distance of travel or subsiding compared to the solids at a higher slurry depth given they have equal free subsiding speeds.
The figure above shows that samples with equal concentration ( in this instance. 25 g/L ) have a invariable or about equal settling-rate. This information can back up some of the statements prior to this portion of the treatment. As stated earlier. speeds of the sample before hindered-settling are changeless regardless of the tallness. Therefore. samples with the same concentration have a changeless subsiding rate regardless of the tallness prior to the hindered-settling government.
A comparing between the speeds matching to the given initial highs can be generated from the figure above. From the graph. the samples seem to hold different initial subsiding rates. Harmonizing to literature. the initial subsiding rate is dependent merely on concentration. But due to little experimental mistakes. the constructed graph above does non clearly illustrate this tendency. Furthermore. it is besides ill-defined how the initial tallness affects the rate at which solids compact. All that is known is that the initial tallness of a slurry does non impact the initial subsiding speed of the atoms ( McCabe. 1993 ) .
A cardinal difference between batch and uninterrupted deposit is that. at steady province. the highs of the assorted zones in a uninterrupted deposit armored combat vehicle are changeless. To maintain the armored combat vehicle running at steady province. the inflow of solids in every zone must about be the out flux. Otherwise. there will be a uninterrupted buildup of solids until sludge appears in the flood ( Foust. 1980 ) . The design of a uninterrupted thickening involves the appraisal of the capacity of the rate-limiting bed or the bed with the least solids capacity. Batch deposit informations is used for this intent and is normally treated utilizing the Coe and Clevenger attack or the Talmadge and Fitch method of finding the thickening country.
As an illustration. the 75 g/L ( test 1 ) slurry concentration informations was used to find the needed thickening country if the slurry were to be subjected to a uninterrupted thickener operation. This peculiar concentration was chosen entirely by virtuousness of its “near-perfect” curve. It is desired that the thicker underflow contain a concentration of 1050 g/L. attained utilizing a provender rate of 50. 000 L/day. and an underflow speed of 3. 472 mm/min. Using the Coe and Clevenger method. the country was calculated to be about 1. 3112m2. This was accomplished by ciphering the entire flux. F utilizing the given parametric quantities and the 75 g/L batch deposit informations. Please refer to the following tabular array.