General Overview, Margarine is a crystallised emulsion of an aqueous
phase (containing milk, water and other ingredients) dispersed in a
fat phase. The fat phase is usually made of vegetable oils but can
also be dairy fat. As a legal requirement, the fat content must not be
below 80% in margarine so any product containing less fat is called a
soft spread. Soft spreads containing less than 20% fat can be
manufactured using modern techniques. The crystallising is achieved in
a Scraped Surface Heat Exchanger. This unit employs a, rotating shaft
inside a barrel having a concentric jacket which contains circulating
secondary refrigerant at reduced temperature. Scraper blades, fixed to
the shaft, clean continuously the inside surface of the barrel as
crystals are formed, preventing fouling and blocking of the heat
exchanger. The semi-solid is made up of crystals whose shape must then
be modified to give the required texture in a worker unit. This unit
also employs a rotating shaft within a barrel but the barrel and shaft
have steel pins arranged along their length in order to impart a
beating action to the crystals. Finally, the product is held for a
period of time in a resting tube in order to dissipate some of the
heat of crystallisation and make the product suitable for packing. The
Armfield Scraped Surface Heat Exchanger unit provides each of these
facilities including the refrigeration plant all incorporated into a
mobile framework. A comprehensive, control console allows versatile
operation and efficient process monitoring. All important process
parameters are variable including scraper and pin worker speeds,
process temperature, barrel pressure and throughput rate., The unit
has been designed to allow faithful reproduction of results obtained
on the full sized plant but on a miniature scale in the laboratory.
Special attention has been given to the instrumentation incorporated
in the design in order, that the user can gain as much information as
possible from the process. Also the refrigeration and secondary
refrigerant circulation systems are incorporated in the mobile cabinet
so that all that is required for operation is connection to a suitable
single phase electricity supply., Description, Where necessary, refer
to the drawings in Equipment Diagrams section 8. This manual describes
both the Armfield FT25BP and the FT25BBP. The FT25BP has one, scraped
surface barrel and a pinworker, the FT25BBP has two scraped surface
barrels and a pinworker. Otherwise the units are identical., 9.1
Overview, The Armfield continuous soft spreads crystalliser is mounted
on a mobile stainless steel cabinet (1), which also houses the
refrigeration system (2) and control panel (3). The feed, pump (6) is
a progressive cavity pump with the speed of rotation (hence the
product throughput rate) controlled from the control panel. Feed
enters the first barrel (7) at the driven end and is subjected to the
mixing action of the rotating shaft (sometimes called a `mutator´ or
`dasher´). As the mix progresses along the barrel it comes into
contact with the cold surface and crystallises. Crystals are
continuously removed from the heat transfer surface, which is hard
chrome plated, by four sharpened, stainless steel scraper blades
coated with titanium nitride. The rotating shaft is driven by a geared
motor unit (8). When the mix has reached the exit of the barrel it is
in a semi-solid, state. The product is then passed to a second
identical scraped surface heat D5937664 exchanger barrel, which is
driven at the same rotational speed as the first. The product
discharges from the second barrel through a stainless steel
back-pressure valve (9). This valve is used to create a pressure in
the barrel, influencing the physical, characteristics of the end
product. Barrel operating pressures up to 8.0 bar (116psi) can be
used, pressures in excess of this being relieved through spring loaded
safety valve (10). After the back pressure valve, the product enters
the pin worker (11) at the front end and exits to the resting tube.
Sampling valves (12) are incorporated after both barrels and the pin
worker. One of the unique features of the equipment is the ease with
which the scraper shaft can be, removed from the barrel. After
checking there is no residual pressure in the barrel, the end cover is
removed by unscrewing the three knurled screws and the shaft carefully
extracted. The floating blades are sharp and care is required to
prevent scratching of the chromed, surface of the barrel. Freezing
temperatures in the two scraped surface barrels are created by a
calcium chloride, secondary refrigerant solution which circulates in
the annular jacket, counter-currently to the feed, entering at the
front (underside) and leaving at the rear (top). Secondary refrigerant
circulation and refrigeration systems are contained inside the
cabinet. This system employs a reservoir containing the secondary
refrigerant circulated by a pump through a plate heat exchanger
wher...