Note: Descriptions are shown in the official language in which they were submitted.
106063~
Thi~ invention relate~ to a method and apparatus
for producing calcium phosphate~ from pho~phoric acid and
mineral calcium compounds. More particularly the invention
related to a method for manufacturing animal feed grade phos-
phates, mono-calcium phosphate (MCP) and di-calcium phosphate
(DCP) or a mixture of these containing P and Ca in a specified
ratio and in a form in w~ich the phosphorus component can be
readily absorbed by the animal organism. Such mineral feod
additives must comply wi~h certain standards of purity in
respect of content of ~luorine, arsenic and heavy metals~
To facilitate handling and use it is important that thes2 feed
grade phosphatee are in ~he ~orm of strong and free-flowihg
gxanulates of appropriate litre weig~t and grain ~ize, and that
they po85e88 good storage propertieg.
The manufacture of such animal feed grade ph~s-
phates by ~eact~oR bet~een phosphoric acid and fine-gralned
mineral calcium compound3 is prior known.
It i~ furth~r ~nown to carry out the reaction by
direct convers~on between a purified, aomparatively concentrated
phosphoric acid and a purified calcium component which may, if
neces3ary, be in ~he form of an a~ueou~ 3u~pension. During
conversion the reaction mixture will ~ir~t pass through a
glutinou~ an~ ~ti~ky phase, a~ter which it will harden as
reaction continu~, Thi8 glves consistency and handling prob- -
lems which cause ~erious troublq during these stages o~ the
reaCtiOn.
.
1060631
When the calcium component i~ pre~ent in the ~orm
of CaC03 considerable quantities of gas will be formed duxing
the reaction, which further increa~es the consi~ten~y and hand-
ling problems in the apparatus. Thi~ i~ probably the reason
why ~o many prior known processes For the man~facture of animal
feed grade phosphate~ prescribe the use of o~her calcium com- -
pound~ which cause less serious consistancy and handling pro-
blems.
The reaction mixture i~ 80 glutinous and vi~cou~
that very powerful mLxing i~ nece~sary during further proces-
sing. In the prior known granulating techniques there are
difficulties in handling -~he mixtuxe without recyclin~ con-
siderable quantities of the reacted product.
The consistency problems al~o make it di~ficult to
achieve homogenisation and proper mixing of the reaction mass.
Local concentrations of acid resulting from inadeguate mixing
w~ll in turn result in a product with inferior handling and
storage properties.
Because of the3e special di~ficulties no one, as
20 far a~ we Xn~w, has yet succeeded in developing 3 simple and
technically reliable process for the manufacture of non-dusting
granulated animal feed grade phospha~es from phosphoric acid
and CaC03. According to South African-Patent ~o 66/7774, which
relates to such a reaction process, the granulating ~tage is
eliminated and the viscous and sticky xeaction mixture is
tran~ferred in~tead to a slow-moving conveyor belt on which
the xeact~on i8 ~ompleted during hardening of the reaction
product. The solid mas~ i8 then arushed by means of rotary
~060631
crusher. However, this result~ in an unsatisfactory product
wi~h angular, uneven grains and con~iderable dust.
According to ~orwegian Patent No. lOQ,875 the reac-
tion i8 carrled out- in the form of a batch process without an
aqueous phase, and with rapid mixing with finely ground lime-
stone and 8~ phosphoric acid in a pan mixer. Agglomerate~
appear for a ~hort period but the~e are broken down by the
mixer as they appear and a ~lightly pla~tic powder i8 formed.
~ particular di~a~vantage in this process is the time factor,
since the reaction requirQs a period of up to 50 hours. Nei~her
~8 the powdered product suf~iciently free-~l~wing, nor is it
particularly ~ui~able for mixing with the u8u~1 animal feed-
stuffs.
However, it i~ al~o a prior known procedure to
reduce the reaction period by ~ilizing a greater amount of
water and using a prior known wet granulation techniqueO The
aqueous reaction components must then be di~tributea in a
greater quantity o~ reacted return material, recyclea from the ~ -
product ~creens to the granulator. Th~ Swedish Patent Applica-
tion No. 340~443/ open to public inspection, relates to such
a proces~, but its workability depends on the u~e of consider-
able quantities of reacted, recycled materlal, as much a9 Up
to 25 time~ the weight of the react~on mixture, during ~he
granulating process. The raact~on components are distributed
such
A in thi~ recycled material. The use of~Y~ recycled material
co~plicates the proce~s and reduce~ tha product~on capacity
of the granulation stage. Clo~e and carefui co~trol of the
reaction condit~o~s with re~pect to ~he wate~/acid ratio,
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reaction times and temperature is also difficult with this process.
The present invention provides a new and improved method for
the production of granulated animal feed grade phosphates from phosphoric
acid and an aqueous suspension of calcium carbonate.
It is the object of this invention to provide a simple and
effective method which is suitable for modern industrial plants, and which
can be employed for continuous and for direct production of ~ree-flowing
granulates in the form of MCP or DCP or a mixture of these, easy to handle
and with good storage properties.
Another object of the invention is to provide a process whereby
a viscous and sticky reaction mixture will not prevent the intensive mixing
which is necessary to obtain a reaction and at the same time achieving a
stable consistency which provides an efficient and controllable process,
giving a solid granulated material with grain size and properties as desired.
A further object of the invention is to provide a process which
can also be carried out with Ca-containing phosphoric acid, a starting
material which when used in conventional animal feed grade phosphate pro-
cesses causes the most difficult consistency problems. -
According to the present invention there is provided a method of
producing animal feed grade phosphates such as mono-calcium phosphate, di-
calcium phosphate or mixtures of same by direct reaction between phosphoric -
acid and Ca-containing materials, characterized in that a finely ground,
preheated calcium carbonate suspension in which at least 97 wt.% of the cal-
cium carbonate has a grain size <50 p, preheated to a temperature in the
range 60 to 100C, is brought to react with a suitable quantity of concen-
trated phospkoric acid, preheated to a temperature in the range 113-132C,
by introducing the reactants into a short, tubular, reaction zone, open at
one end, whereby development of gas and intensive mixing of the reactants
in the reaction zone take place, the gas formed expelling or ejecting the
foaming reaction mixture from the tube-like reaction zone, the reaction being
~ - 5 -
"E~
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substantially completed while the individual particles in the mixture are
freely suspended in air or gas, whereafter the reacted mixture is collected
in the form of a free-flowing granulate having improved handling properties.
The reaction between phosphoric acid and calcium carbonate to
form mono-calcium phosphate (MCP) or di-calcium phosphate (DCP) proceeds as
follows:
- 5a -
,
.
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MCP: CaC03 + 2H3P04 - ~ ~a(~2P 4)2 2 2
3 H3P04 --I-v~ CaHP04 + C02 + H20
When u~in~ Ca-dontaining phosphoric acid, for
example containing Ca from a preneutralising plant or Ca
remaining in tha dige~tion liquor ~rom ~he O~da process, it
i~ found tha~ with the method a~cording to the invention,
Ca~H2P04)2 in the acl~, even in a precipitated state, will
be conver~ed as ~ollows:
Ca(H2P04)2 + caC03 _-~ 2~aHP04 ~ C02 + H20
By us~ng preheated reartants an aqueou~ su3pension
of ~inely ground calcium carbonate can be causea to react ver~
rapidly with pho~phoric acid with vislent ~ormation of gas an~
~cam. According ~o thQ invent$on ~uch violent reaction between
hot reactants i8 utili~ed in a very ~pecial mànner, whereby
there taXes place ~h intensive mixing o~ the reactant~ without
the aid of power-co~sum~g mechanical mix~r~ and where the
reaction mixture shortly afterwards i9 discharge~ or expellea
.
to the air~ Most df the readtion takes place while the ~ :
:reaction mixture i suspended id ~he air in the form o~ :
eparate drops oP foam. It i9 during this stage that the
: 20 ~tlcky consistency normally occurs, and which ha~ been de-
s~ribed above as c~itic~l with ragard to mixab~lity, require-
ment~ of power, etc. Whan the brief period of suspension i8
.
: over the reaction mixture has the form of a moi~t, nGnfitldky
grain material.
: The ~roce~s accordlng to the invention i8 parti-
cularly characterised by employing a preheated, aqueous
';
: ~,
, ~.
1060631
su~pension of fine-gra~ned calcium carbonate which ~ brought
to react w~th preheated phosphoric acid by introducing the
reactant~ into a short,. tubular.:~eac~ zone~wh~e~bhe resulting
gas e~o~ution cau~e~-e.~ intengive mixing and aqit~ting o~ the
reactants, and where the gas further causes a high pressure
whi~h shoote~ or jettisons a foaming reaction mixture out of
the ope~ ~nd o~ the tubular reaction zone, the reaction being
almost completed while tho d~veloped drops of reaction mixture
are in free suspension, w~ereafter they are collected in ~he
form of moist, non-sticky particl~s.
Further ~pecial characteri~tics of the invention
wlll appear below especially in connection with the accomp~ny-
iny patent claims~
The method and apparatu~ will now b~ de-cribed in
conjunction with the accompan~ng drawings wXerein $~g. ~1 is
a ~chematic and simplified flow diagram, and ~ig. 2 a sectional
view through a tube reactor sultable for carr~lng out the method.
Fig. 3 is a croi~ sectional view thxough the same ~èactor along
the line a - a in ~ig. 2.
~0 Fig. i shows a fe~ }ine 1 for ~alcium carbonate
~uspension and another ~eed line 2 for phosphoric acid. A pump
- 3 pumps the hot chalk æu~pQnsion tHrough the line 1 to a short
tube reactor 5, the desSgn a~d mode of operation of which will
be de~cribed în more detail below.
Hot phosphoric acid îæ pumped through l~ne 2 to
the reactor S by means of a pu~p 6, and the two reactant~ are
thoroughly mixed in the reactor and gas and foam are formed.
... , . . . , . . . - , .. .. . .
; 1060631
The reaction mixture i~ then expelled through the open end of
the reactor into a chamber 7 where the ~tream disintegrate~
into particles which are freely suspendad in gas until the
reactton product fall~ down and i8 collected in a collecting
devise 8. The upper end of the chamber iQ fitted with a ga~
outlet which i~ connected to a cyclone separator and an exhau~t
fan 9. When it falls to the bottom of the c~amber 7 the animal
feed phosphate i8 in the form of a moist, but ~ree-flo~ing
product. With ~uitable control and regulation of the reacti~n
conditions is obtained a product which i8 asy to handle and
which can con~ain all desired Ca/P ratios.
Because of the development of gas during the
reaction between phosphoric acid and calcium carbonate the
product will have a somewhat vesicular structure with gas-
filled pores, which at times may be too light for direct mi~ing
with the other components in some type8 of anlmal feed mlxtures.
H~wever, the moist primary material obtained in the first stage
of the process is also very ~uitable ~or further processing as
well a~ for granulating w~th other mineral gubstances and
tracers; which may be ePfectively mixed in the recycle stream
prior to the mixihg and collecting device 8. The invention
therefore provides a method which makes further processing
possible and enablé~ t~e p~rou8 ~ruct~re to be bro~h ~own,
whereby a granulate with a higher litre w~ight can be produced.
The intormediate product from the collecting device B is di~-
charged via a disc feeder 10 which ensure$ free flow from a
w~de opening. The desired depth of the material above the
106063~
disc feeder is achieved by mean~ of a level indicator ~not
shown in ,the drawing) controlling the ~eeder's scraping off
position. The chamber is further provided wlth instrum~ntation
which enables a controlled flow of air to pa~s through the
porous, hot and somewhat moist product near the outlet. The
product is then compacted in a continuously operating qingle
or multistep pre~s ll, from wh,~ch the material in the form
of pres~ed flakes i~ led to a granulator 12, ~here it is gran-
ulated in its moist state. A high yield of a non-dusting fine
granulate is thereby obtained! which i8 ~ent through a dryer
13 and then a screen 14, whereafter the free-flowing, non-
a'dherin~ granulate i8 tran~ported to Qtorage. '
The tube reactor 50 is Qhown in more detail in
Fig. 2 and 30 It consists of three main sections, a mixing
chamber 55, a pre~su~e cham~e~ 56 and a discharge tube 53.
T~o separate feed line3 51 and 52 direct the reactants tang-
ent~ally into the m~Xing chambe~ 55 (Fig. 3) in such a way as
to ca~e a powerful t~rbulence and mixing as the formation of
g~s i~c~ease~ ln inte~s1ty. A high pre~su~ iB generated in
the pressure chamber 56, which pressure expells and accelerates
the flow of foaming mixture through the someahat narrower out-
let of the discharge tube 53. This tube is pre~erably detach-
able from the pressure chamber and may be given various con-
structional forms. The cros3 section and the total reactor
volume salected may be such that ~here is optimum initial
velocity of ~he rea~tion mix~ure in relation to ~he reactants'
rea~ivity. The choice of materials in the reactor i8 not
crit~cal and the outl~t may be o poli~hed steel, Teflon or
106063~
some other pla~tic or rubber material, Plastic and rubber
materials are prsferred if the components in the mixture have
a tendency to deposit layers in the inside of th~ reactorO
At the re r, ~losed end of the reactor a rod 54 is arr~hged,
which can be used to keep the reactor open if it becomes
cloggea as a result of an unexpected shut-down of the system,
etc.
Examples:
1 (.M.C.PL
55,1 kg/h of precipitated calcium carbonate, ground
to an average grain 9i2e of 15 - 20~ and with a maximum
particle ~ize of about 50~was used in the orm o~ ~ 60%
suspension in water. The temperature was 90 3&, and the
suspension was fed continuously to the reactor together with
127.5 kg of phosphoric acid per hour at 116+2C. The acid
containod 82~/o ~3P0
184 kg/h of a product con~aining 21~/o ~2 was
obtained prior to the granulating process. The carbon dioxide
content was 0.6% and the material was well suited for transport
and handling, and eventu.al granulation. It wa~ ea~y to dry
the product continuously to a water content of below 1.4%.
After drying the partic~es we~e strong ana dense. The P con-
tent in the dried granui~te w~s 22~/o, The w~ight radio of
Ca/P was 0.71.
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? (MCP)
Calcium carbonate of the same finenes~ a~ that
used in Example 1 w~ reacted with a less condentrated phos-
phoric acid, which resulted in a more aqueou~ reac~ion product.
141.8 kg of 74O5% ph~sphoric acid and 88.8 kg 64.5% calcium
carbonate suspension per hour w~re f~d to the reactor which
was operated at a pre~sure of 3.2 ato. Thi8 resulted in a
very fine-grained reactor product having properties which
made it ~uitable for further hanaling and granulation~
3.(MCP)
Calcium carbo~ate of the same origin a~ in Example
1, but with an average grain size of about 50~, wa8 processed
in the ~ame pilot plant. The concentration ana quantity of
the ~u~pension were the ~am~ as in Bx~mple 1, ana the temper-
ature wa~ 87C. The acid content Wa5 the same as in Example 1,
and the temperature wa3 117l1& . The drying process was time-
consuming ana the product was incompletely dried. The product
wa~ sticky and ¢orrosive and contained 3.~Y0 C02. The sticXi- ~-
ne~s proved to be a nui~ancG during a subsequent granulation
proc~ss.
4 (DCP~.
The follow~ng example and Example 7 ~how how t~e
DCP was produced: A product with low P-analy~ wa~ ~oduced in
the same apparatus as used in the aforementioned example~, by
reacting an lncrea3ed quantity of carbonate with phosphoric
acid.
11 . .-
~060631
Precipitated cal~ium carbonate ground to 98h under
20~, corresponding to an average grain size of 4 ~ 5 ~, wa~
used in a 5~/0 suspsnsion in water. The suspension was heated
to 65C only, and 177 kg~h was fed to the reactor. llO kg~h
of an 87.6% phosphoric acid at a temperature of 113 C was fea
to the reactor.
The reaction product contained 3~/0 H20 and l.~/o
C02~ and Wa8 suitably plastic for granulation. With a weight
ratio of Ca/P = 1.4 the aAalysis of the dried product showed
18~/o P and 26.5% Ca.
5 (MCP)
Precipitated calcium carbonate of prac~ically the
same fineness as that used in Example l was prepared as a
42.6% suspension in water, and a quantity of 54 kg/h was fed
to the reactor at 92& . In order to produce `an a~imal ~eed
grade pho3phate containing about 24% P this ~u~ntity o~ chalk
wa~ reacted with an F-free, Ca-containing pho~phoric acid at
128 & at the rate of 128.6 kg/h. The P-content of the acid was
25~gYo and the weight ratio o~ Ca/P was 0.43, 80 that the pro-
duct's Ca/P would be close to 0.70.
Reaction velocity was satisfactory, and the
plasticity and the water content of the r~action product mads
it w~ll suite~ ~or ~ranulation (with 18.5% H20). The product
contained 0.6% C02 as a result o~ non-converted CaC03.
12
1060631
6 (~CP?
The same grade of calcium carbonate as U8ad in
Example 5, but in a less agueous ~u~pen~ion, 60% caco3~ Wa5
reacted with the same acid and un~er the ~ame conditions and
temperature~. Reaction was sl~w and incomplete. The product
was unsuitable ~or granulation and was found to contain 2.5%
C02. There waæ a considerable degree of delayed reaction
when the product Wa8 further processed.
7 (DCP)
Calcium car~onate of an average grain size of
10 - 15~, bu~ in a 46~/o suspen~ion fed a~ the rate of 159.6 --
kg~h wa~ advantageously reacted at 98& with 129.1 kg/h of
Ca-cont~ining phosphor~c acid with Ca/P = 0.322 and a total
of 25.~/o P. The temperature of the acid was 132& . The more
time-consuming reaction did not prevent the further processing
of the reaction product ~th about 35% ~2OD W1~h a C~P ratio =
1.22 ther~ wa~ n~ aci~ rasidue gi~ing ~rouble, in 6pieY~ of
a noq-reac~Ed quantity-of carbona-t~ giving a C02 an~lysig
o~ 1.7%. '
The greater quantity of watex removed during drying
reQulted in the product having a weight of 750 g per litre when
all particles ~nder 0.1 mm and o~er 1.5 mm *ere remo~e~.
Particle itrength ~as also s~m~wha~ weak compared with a pro- -
duct wi~h a lower Ca/P ratio. A product sample with ~% H20
(determined ~y drying for 3 hours a~ 105 &) had a P analysis =
20.1%.
13
1060631
8 (Storaqe te~t82
Various qualities of the animal feed grade phos-
phate~ were stored for 12 weeks under fluctuating climatic
condition~. The bags were placed in hydraulic presse~ under
a pressure of about 1500 kg. The calcium phosphate3 had a
Ca/P weight ratio of 0.7 - 1.3. There were no particles over
1.5 mm. Those below 0.1 mm accounted for 1 - 2~/o and the
water content, determined by drying for 3 hours at 105 &, wa8
0.4 - 4.9.
Mixtures containing up to 33% finely crushed lime-
stone and up to 6% powdered MgO w~re also prepared from the
same products. Only one showed 8ign8 of caking after 12 week'~
storage, Thi8 was a deliberately poorly dried and dusty MCP,
mixed with limestone (l~/o dust and 4% water).
~ ixtures ~ontaining MgO sh~wed no signs o caking,
neither did MCP alone, even with 2~/o dust and 5% H20.
All percentageæ given in the above examples relates
to weight per cent.
It i8 important that the calcium carbonate ~s
sufficiently fine-grained. Tests have been made with variou~
grain sizes, and a grain size preferably of ~ 50~ wa~ found to
be nece~sary. The pref~rred average grain size le in the range
~20~) . A very finely gxound quality with 98 wt.% of grain
s~ze ~20~ and an average grain si~e of 4 - 5~ also resulted
in a completely satisfactory end product. Thi~ is a mNch more
finely grained material than is u~ed in other prior known
14
1060631
commercial proces~es, where in order to prevent consi~tency
problems coarser particle~ are used to prevent too rapid a
reaction~ Increased quantities of water result in more rapid
reaction. However, it i~ no~ possible to make use of this
advantage in order to use much coar~er calcium carbonate,
becauQe the carbonate will not be 3ufficiently reactive.
Mineral as well as precipitated calcium carbonate
may be used. The latter may be calcium carbonate converted
from cal~ium nitrate Ca(N03)2 from the Odda process with NH3
and C02.
As already mentioned, the process i8 al60 flexible,
since MCP or DCP or other "more average" qualitie~ can be
manufactured, m e f}exibility of the process in respect of
raw materials has already been de~cribed. Both Ca-free and
Ca-containing phosphoric acid have proved to be ~uitable, the
quantity of CaC03 being corre-Qpondingly r~duc~d iin rola~iQn to
the amount of calcium contained in the phosphoric acid.
In both ~ases the Ca/P ratios in the product may
be selected as de~ired.
Commercially availabl!e type~ of pho~phoric acid
meeting th~ previou~ly mentîoned ~equirements in re~pect of
purity will be comparatively ~onc~nt~ted. Mo6t o the tests
have b~en carried out with two qualities of phosphoric acid,
purë p~o~phor~ a~ia ~on~aini~ from 74 - 88 wt.% of H3P04
and Ca-containing acid produced from the Odda proce~ digestion
liquor. Neither type Wa8 diluted and both reac~ed satisfact-
orily.
,: .
.~
1060631
More aqueouq t~pes of acid may also be u3ed provided they
otherwise ~ati~fy the requirement~ as regards quality, Adjust-
ment of the water content of the chalk su~pension, and adju~t-
ment of other proce~s variables ensure the desired reaction
velocity and consistency if the process described is adhered
to.
Ca-containing acid, which gives ri~e to the most
difficult consistency problems when used in the conventional
manufacture of animal feed grade phosphate~, is surprisingly
easy to employ in the new proce~.
However, it i~ important that the Ca/P weight ratio
is not too high, and according to the inventi~n it has been
~ound bas~ to em~loy ~ C~/P radio 0.45. The phosphoric acid
and the chalX suspension axe preheated before being introduced
into the reaction zone. ~e have usQd temperatures of 65 -
100C in the ca~e of the chal~ ~uspen~ion and 113 - 132C in
the case of phosphoric acid. This meets the requirements
with regard to de~ree of reaction and product consistensy with
calcium carbonate of reasonable grain fineness. If the calcium
carbonate i8 very finely ground the temperaturQs may be corre-
spondingly reduced 80 that the desired reacti~ity is always
easy to achieve.
16
