Dog's Master wrote:
Dear Colleagues, distillers and rectifiers
I promised to do a little esse about SPP and I fulfilled my promise.
See it in attachment.
Sorry for my English, if somebody can correct it I will be grateful
Maybe there you will find some answers you want to find
Cheers!
I realized that pdf is not acceptable, so here is my esse:
Why I prefer to use spiral-prismatic packing.
Before you do anything, should clearly define the objectives, the costs of
achieving these goals and desirable ratio for the price - quality.
Outlined below - my personal opinion. But they are backed by a reputable
literary sources (Stabnikov, Krehl, Bagaturov) and personal experience, and
therefore may deserve consideration.
If we are talking about the spiral-prismatic packing, we mean that our goal -
to obtain a neutral alcohol of high quality. When we have special needs and use
special modes of operation of the column - we can produce fruit and grain flavored
spirits also.
Q-1 What characteristics should have a packed column and
the actual packing?
1. Minimum resistance for vapor. Packed column working in film mode.
The flow of the film reflux unseparably, laminar. Flow regime - waveless.
According to experimental data, the optimal rate of steam is about 1.5 m /
s, ie very little. This means that the cross-section of the column should be free to
the maximum.
2. With a minimum of volume our packing should be characterized by a
maximum surface. We know that the interaction occurs at the interface between
liquid and vapor.
3. The surface of the packing must be very good for retaining fluid.
4. Packing should have a good heat conductivity. This is dictated by the
fact that good thermal conductivity makes it easier to transfer heat to liquid film,
and it is easier to evaporate.
5. Packing must be chemically inert, should not make harmful impurities
and to change the taste of alcohol.
6. Easily washed when needed.
Q-2 What we must avoid when designing a packed column.
1. Should fully weaken the influence of wall effect, ie the desire to fluid
flow along the walls of the column. For this purpose it is necessary to arrange
high-quality insulation and direct the flow of phlegm in the center of the column by
means of special devices.
2. Avoid creating channels for the fluid in the packing, so-called “preferred
paths”. This can be achieved only with the help of correct choise the shape and
diameter of the packing with a well-wetted surface.
Channeling stops when dc / dp> 10 (dc-dia of column, dp-dia of packing)
Specialists in laboratory distillation knows the so-called "rule Hubert",
dc / dp = 10-30.
3. Should not allow non-uniform, layered styling packing. It also causes the
appearance in the column “preferred paths”.
4. When selecting attachments aspire to the angle of the surface tension was
minimal, as the surface tension forces are entirely determined by shared properties of
the mixture.
In stainless steel angle of - 83 degrees, with frosted glass - 20. But glass
loses in the heat conductivity, and therefore, our decision is to use steel, that conducts
heat well, we have to do specially prepared (grass) surface of the packing.
5. Afraid as a fire nonvertical installation of the column. Otherwise, fluid
will flow mainly on the walls. You just guaranteed this inconvenience. Use a plumb
or level when installing the column into position!
6. Must provide an needed amount of phlegm in the correct place. It is also
easily solved. In the upper part of the column phlegm feed tube, preventing its contact
with the wall.
Column necessarily need to be divided into parts. Phlegm in partitioning
have to be redeployed again in the center of the nozzle.
It makes sense to do, since the workload on the column partitioning can
reduce the HETP. Partitioning can reduce the height of the column while maintaining
the quality of separation by 30%.
This, in particular, are devoted to Kazan, who investigated the near-wall
effect in the laboratory. Effectiveness of its non-partitioned column on the
separation of a mixture of hydrocarbons was 18 HETP. After dividing the column
into three sections, it increased to 24 HETP. With spirits the situation is better.
Q-3 What can we obtain, using spiral-prismatic attachment.
Consider a column of 40 mm in diameter. Its cross section is equal to 12.56
cm2. Let us remember that figure.
Let’s see what facilities we will be able to work using a variety of packings,
if the optimal rate fo vapor is 1,5 m / s, and at 1 kilowatt heater power produce around
45 liters of vapor per minute, or 750 cm 3 / sec.
If the column is empty, then we are at a speed of 150 cm / s in 1 second
would have let through the cross section of the column 1884 cm3 of vapor, which
corresponds to the power of 2.51 kW.
At this stage, are visible benefits of properly made spiral - prismatic
packing. It is, on average, leaving 86% free cross section of the column, that is, allow
us to work with a power 2.51 x 0, 86 = 2.15 kW.
If in the same column load glass balls 4 mm in diameter, often used by
artisan distillers, they will occupy 74% of the cross section of the column. This means
that the maximum capacity will be in the case of balls of 2.51 x0, 26 = 0.65 kW, which
is in excellent agreement with experimental data.
So the first conclusion in favor of the spiral - a prismatic attachment: it
allows equal power to use a less diameter tube, that means - to save on material.
Becomes clear why is unacceptable use of expanded clay, broken glass,
pebbles, marble chips and similar materials. They almost completely cover the
cross-section of the pipe, or vice versa, leave it too loose, often crack from
temperature fluctuations and crumbling.
Usage of scrabbers made off stainless steel looks better. But there is too big
risk of channeling fnd simply buying low quality chinese production made from
unknown metal and with unknown surface, that makes almoust impossible to
accurately calculate the parameters of the column.
A few words should be said about the surface area of SPP packing. Virtually
the same will be the interface between two media - the gas and liquid.
• In the first approximation we can say that the surface area of packing
contained in a unit of volume determine the separation ability of column.
And that’s exactly the aim for which we are doing the column.
At the same time, the balls 4 mm in diameter, which we mentioned earlier,
have a surface area in one liter of 0.9 m2.
Very expensive glass Raschig rings in one liter of surface separation are
equal to 1.1 m2.
The second conclusion in favor of the spiral - a prismatic packing: it
provides a separation in 1,5-3,5 times better than its nearest competitor.
Q-4 Retention ability of packing.
After properly designed experiments it appears that the spiral-prismatic
packing can hold 94-96 grams of water per liter . This is when the packing thoroughly
blowed out, imitating the passage of steam. If you do not blow, then the retention
capacity raises up to 200 grams.
In addition to static retention, spiral-prismatic attachment is characterized
by a dynamic of containment. For a theoretical plate, this value comes to 3.5 grams (
according to Krehl).
Static retention capacity of spiral-prismatic packing, etched properly, only
slightly inferior to the static retention frosted glass and higher retention of china.
Q-5 Thermal conductivity.
The thermal conductivity of stainless steel is 35 W / (m • K) that is higher
than the thermal conductivity of glass (the most common material for making beads,
Raschig rings and some other types of packing), which is equal to 1.15 W / (m • K)
Consequently, the steel packind is about 30 times better conductor of heat
from hot vapor to a liquid film that completely compensates for its lack of wet ability.
Q-6 How much does it cost?
If the height of the filled volume of the column of 1 meter, the volume of
the nozzle is equal to 1.26 liters. I remind you that we are talking about a column
40 mm in diameter, optimal for domestic usage.
Volumetric weight of the packing after etching and seals - about 900
grams per liter. Price of stainless steel wire 0,2 mm thick in our area - about $ 20
per kilogram.
On our column will need wire for 22 dollars 68 cents. Etching will be
worth about $ 6 - reagents are dangerous, they must be thoroughly neutralized and
rinsed. The process of neutralization is much more expensive than the actual
reagents. Manufacturing does not cost anything - you do it yourself!
Equipment for one usage is worth almost nothing, because at the end of
the process the machine will be dismounted. Even if you buy at the flea market the
remains of an electromagnetic lock, sealed switch, a small permanent magnet (for
example, to keep the doors of the cabinet), these expenses do not accurately pierce
a hole in yours budget.
Total packing cost 6+ 23 = 29 dollars. Inexpensive, since it allows you to
make a completely professional equipment and save a decent amount of money
thanks to reducing of the diameter of the main column, adapters and fittings.
Thanks for yours attention!
Riku, what Dm seems to be saying here about the efficiency bebnfits of different packings seems to be to be best tested by finding the limit of packing height or hetp. That's the claim, that the hetp is better for spp.
So i'd be thinking that the best way to test if this was tue would be to use a modular column. One that clamps together in sections...
Do a run with scrubbers in a 600mm column, do one with spp. If both pull 95+, take 100mm of packing out of each. If neither get 95+ add 600mm more...
This will quickly draw the lines as to how high a hetp is for each packing type and how much more efficient it is.
Seems to be more sense than measuring output volume.
I was actually trying to find where he discussed the application and theory of the etching, i was sure he gave figures for the increase in surface area and hetp and that they were very significant. Can't find it with a scan of the 7 pages though, i'm thinking it may be in another thread.
He did say it was nessercary to derive the maximum benefit.
