FICHA DE RIESGO

Materials of construction

The choice of the material of construction (Table 8.1) of an auto-clave depends on the operating médium whether acidic or alkaline, the temperature range, and the presence or absence of oxidizing atmosphere. Table 8.2 provides a set of multipliers which can be used to convert 350°C pressure ratings for any T316SS vessel to higher or lower temperatures. It can also be used to determine the corresponding ratings for vessels of the same design made of other materials. No reactor or pressure vessel should be operated above these máximum temperature limits.

Stainless Steel 316

At ambient temperatures stainless steel 316 offers useful resistance to dilute sulfuric, sulfurous, phosphoric and nitric acids, but sulfu-ric, phosphoric and nitric acids readily attack T316SS at elevated temperatures and pressures. Halogen acids attack all forms of stain-less steel rapidly, even at low temperatures and in dilute solutions.

Although T316SS offers excellent resistance to surface corrosión by caustic stress corrosión cracking can occur in pressure vessels. This phenomenon begins to appear at temperatures just above 100°C.

T316SS offer good resistance to ammonia and to most ammonia compounds, Halogen salts can cause severe pitting in all stainless steels. Chlorides can cause stress corrosión cracking, but many other salt solutions can be handled in stainless vessels, particularly neutral or alkaline salts.

Carpenter 20Cb-3

is an enriched grade of stainless steel, designed specifically for use with dilute (up to 30%) sulfuric acid at elevated temperatures. It can also be used for nitric and phosphoric acid systems as well as for all Systems for which T316SS is suitable.

Table 8.1 - Materials of construction for Parr laboratory autoclaves

T316 Stainless Steel Carpenter 20Cb3 Titanium Grade 4 ZIrconlum Grade 705

Fe

Major elements, % Cr

Table 8.2 - Pressure rating rectors (Parr Instrument Company)

T316 Stainless Steel Monet 400 Titanium Grade 2 Titanium Grade 4 Zirconium Grade 705

25

200 Pressure Hydrometallurgy Chapter 8 - Lab Autoclaves & Pilot Plañís 201

Monel 400

is an alloy comprised essentially of two-thirds nickel and one third copper. For many applications it offers about the same corrosión resistance as nickel, but with higher máximum working pressures and temperatures and at a lower cost because of its greatly improved machinability. It is widely used for caustic solutions because it is not subject of stress corrosión cracking in most applications including the pressure of chloride salts. It is also an excellent material for fluo-rine, hydrogen fluoride and hydrofluoric acid systems. It offers some resistance to hydrochloric and sulfuric acids at modest temperatures and concentrations, but it is seldom the material of cholee for these acids. As would be expected from its high copper content, Monel 400 is rapidly attacked by nitric acid and ammonia systems.

Inconel 600

is a high nickel alloy offering excellent resistance to caustic and chlorides at high temperatures and high pressures when sulfur compounds are present. In caustic environments, Inconel 600 is unexcelled. It also is often chosen for its high strength at elevated temperatures. Although it can be recommended for a broad range of corrosive conditions its cost often limits its use to only those ap-plications where its exceptional characteristics are required.

Hatelloy B-2

is an alloy rich in nickel and molybdenum which has been developed primarily for resistance to reducing acid environments, particularly hydrochloric, sulfuric and phosphoric. Its resistance to these acids in puré form is unsurpassed, but the presence of ferric and other oxi-dizing ions in quantities as low as 50 ppm can dramatically degrade the resistance of this alloy.

Hastelloy C-276

is a nickel chromium-molybdenum alloy having perhaps the broad-est general corrosión resistance of all commonly used alloys. It was developed initially for use with wet chlorine, but it also offers

excel-lent resistance to strong oxidizers such as cupric and ferric chlorides, and to a variety of chlorine compounds.

Nickel 200

is one of the designations of commercially puré nickel. It offers the ultímate in corrosión resistance to host caustic environments, but its applications are severely restricted because of its poor machinability and resultant high fabrication costs.

Titanium

is an excellent material for use with oxidizing agents, such as nitric acid, aqua regia and other mixed acids. It also offers good resistance to chloride ions. Sulfuric and hydrochloric acids, which have high corrosión rates in their puré form can have their corrosión rates in titanium reduced if small quantities of oxidizing ions, such as cupric and ferric are present to act as corrosión inhibitors. This phenom-enon leads to many successful applications where sulfuric acid is used to leach ores and the extracted ions act as corrosión inhibitors.

Prospective users must remember that titanium will burn vigorously in the presence of oxygen at elevated temperatures and pressures.

While there have been many successful applications in hydrometal-lurgy where oxygen and sulfuric acid are handled in titanium equip-ment, the danger of ignition is always present and must be protected against.

Commercially puré titanium is available in several grades. Grade 2 is the material most commonly used for industrial equipment since it can be fabricated by welding and is approved by the ASME Code of Unfired Pressure Vessels. Grade 4, which has slightly higher trace levéis of iron and oxygen, has higher strength than Grade 2 but it is not suitable for welding and it is not covered by the ASME Code.

Since Parr vessels are not welded, they usually are made of Grade 4 to obtain higher working pressures than can be obtained with Grade 2. Grade 7, containing small amounts of palladium, and Grade 12

202 Pressure Hydrometallurgy

containing small amounts of nickel and molybdenum, offer enhanced resistance to certain environments and can be used for Parr reactors and pressure vessels if suitable billets can be obtained.

Zirconium

offers excellent resistance to hydrochloric and sulfuric acids but as with Hastelloy B-2, oxidizing ions such as ferric, cupric and fluorides must be avoided. Zirconium also offers good resistance to phosphoric and nitric acids, and to alkaline solutions as well. Two different grades are available. Grade 702 containing hafnium is the standard commercial grade offering the best resistance to most cor-rosive agents. Grade 705 containing small amounts of both hafnium and niobium has better strength than Grade 702, allowing higher working pressures when it is used in pressure vessel construction, but the corrosión resistance of Grade 705 is not quite as good as Grade 702.

Carbón steel

is usually used for laboratory reactors only when it is desired to duplicate construction material used in plant equipment, Because it rusts easily, carbón steel vessels are not carried in stock and must be made to order, often resulting in costs higher than for stainless steel equipment despite the lower material cost for carbón steel.

Agitated autoclaves

These are versatile laboratory reactors available in 100 mi up to 2 litres from Parr and in large sizes from Autoclave Engineers. They can be quipped with gas inlet tube, cooling coil, agitators, etc.

(Figure 8.1). Berghof autoclaves incorpórate an interchangeable, completely pore-free, chemically resistant PTFE lining, covering all interior surfaces. The stirring system does not use a packing gland or magnetic drive; a three-phase induction motor provides reliable stirring, even under heavy load. Reactor operates up to 20 000 kPa and 250'^C. Berghof developed a special conical flange closure

Chapter 8 - Lab Autoclaves & Pilot Plañís 203

which assures uniform tightening and a reliable seal by means of two simple hand screws.

Pressure g^ge has stainl«is sfeet tube and socket

Sttrrer drive turns on balj and needle bearíngs in steet hiib

Cones of a Teflon-base píasfic form gas-iíght giand on sfírrer shaft

Gas reléase *'aive

Water connecfton to cooling channe! around paclctng gland -—

Bomb head is clamped to cyíínder by tightening six cap screws in pair of steeí ring sectíons

Heavy steel band holds the clamp ring sectíons in position

Stirrer beartng braclcet is clamped to fhermoweÜ Thermowelí extends to bottom of cyíínder for femperafure measurenríents with either a thermometer or a thermocoupii

Safety ruptura dtsk protects against accidental over-pressure

• Compressed gas conneitíon ts made to threaded opemng in valve body

Gas ínlef val^e

^ „ ^ L ¡ q u í d sampliiig valv»

Two-piece threaded adapten seal valves and gage fo head, factng ín correct positíon

Cyíínder h machined írom soiid hot-roíied bar of T3[6 stainless steel. afío from other corrosíon-resístant metáis tíné alloys

Stirrer shaft turns in replaceable Teflon bearíng

Gas iníet and ¡tquid samplíng tube

Two 6-b!ade propeíieri agítate the reactants with a turbulent dowo-fhrusf. Propellers are adjustabie on stirrer síiaff

Figure 8.1 - Two litres Parr autoclave

204 Pressure Hydrometallurgy

TT

Figure 8.2 - Cooling coils

Chapter 8 - Lab Autoclaves & Pilot Plañís

Gas reléase valve"

Safety rupture disc

Wning shaft

Lowerguidebearing

205

Pressure gauge

Stirrer drive system

Gas inlet valve

Uquid

sampling vaive

Thermocouple

Dlp tube connected to both the gas inlet and liquid sampling valves

Figure 8.3 - Autoclave head

206 Pressure Hydrometallurgy

J

Figure 8.4 - Bomb closure details

Figure 8.5 - Assembled unit

Chapter 8 - Lab Autoclaves & Pilot Plants 207

Oi S6a! hoips pfotocl ihe gauge agalnst corrosivo VJ^KHJTS,

Electric t>&ating of vapour fackMs

A iharmooouptewithtn a th«rmocxHiple

\r\ cnJer to carry sway fnciton haal ^enerated at IJw packing. the drtve shah is dniled out, srxj by mear»

o( £ (otix seal, a cocsteni ttcw oí waier a cinxttatad Bhrough the drive shaíl ín tfis packing se:[ion.

Heawy-duly tíirust bearings insure long-iffe operatlon.

Provisión ts (nade lor padung tensión taKe-up. wNch allfjws foF easy maintenance and long t<ie.

The padtlr>9 hDf standard auiociavfis is micki (rom tcítov-astíestos. Tho coinbinatiofi ol low cooliicwnt ot fric^in and high-corrosion roslstanco próvidos pacKlng wHblowí^raíing tamporalure. long Uto, nigh slrongih.

and nnJríimuRi friciionai wear on iho drivo shall.

Orive sKait

SoWs clrarging

The siarxiard ctosure bollad confinad gasKel type

Safety ^ a ü assembly

Cooling cotls

Sannpíing

BSow pipe or drain conrMCtion can be pcovided tor emptying Iho autoclavo wtthoul removal oí cover.

This is a turblne-type agitator mtn a tvMwí shait used in cotijunciioh wiih rerrMavaW* bafflas.During opecaEion, s low-pfassure atea ts created ai ¡tío aitt>ine Jrt)pellor.

Gas is «Dosaquenily drawn dovm Ihrcugh iho hoíiow shan and dJspeised (hroughoui the íiqu«i- Tho gas bubbles are t>rai(«n up by the t>airte^

Figure 8.6 -Autoclave Engineers

208 Pressure Hydrometallurgy Chapter 8 - Lab Autoclaves & Pilot Plants 209

I LITER

1 GALLÓN

Figure 8.7 -Autoclave Engineers

J

5 Gallons

Figure 8.8 -Autoclave Engineers

210 Pressure Hydrometallurgy Chapter 8 - Lab Autoclaves & Pilot Plañís 211

10 Gallons

Figure 8.9 -Autoclave Engineers

ORIVE SHAFT - LOW£R SECTOR 516 S.S.

SPACEB- 316 S S , _ RETAiNiniO RiWG 18-1

[16) t - t / 4 - 8 H e x , SOC CAP SCRS.

C0VCT-Sft24O r y P E 3)6 S.S-SASKET-16-e BO0r-Sfti82 QR-t^Ste

MOTOR SUfPORT OWG.*

i-\/2 H.P MOTX)ft-a. i, GR R 2 2 0 W 4 0 VOLT- 60 CYCLE - 3 PHASC H40 Í?,PM FRAME * L. ALUS MOTOR

_ AGlTATOR 5HAPT- 316

S.S-24 STR1P M E A T E R S - I O O O WATTS EACH - WIRED IN 2 BANKS OF 12 K.W, EAW - 220 VOLT s^3 PMASE SERVICE

STAND STEEL

30 Gallons

Figure 8.10 -Autoclave Engineers

212 Pressure Hydrometallurgy Chapter 8 - Lab Autoclaves & Pilot Plañís 213

msss-xiLjsasmi- Zipper Clave

This Autoclave Engineers reactor is manufactured in 2, 1,2 and 4 liters. It is claimed to be the fastest, easiest, opening and closing pressure vessel ever offered. No bolts to torque, no clamps or rings.

Instead, just raise the body and push the spring section to cióse the cover. To open, just pulí the spring and lower the body. Cover re-mains stationary, so there is no need to break cover connections.

1 ^ ^ vm.<«-m»s «TI

ü

f í O r o B 5W«»C«T 2 «P »OTOB-»00 fiPM

^ ^ • 4 0 «t.T-3 «^Mt to CTCLE a, '.-„'>f

O-Zip . . .

Insert the cover, zip the Zipper, it's shut.

Un-Zip

Pulí the Zipper, Í; raise the cover,

it's open.

Stationary outer tiousing (no sheaves or boltguard needed)

500 mi ZípperClave system

Figure 8.13 - 500 mL Zipper Clave system

50 Gallons

Figure 8.11 -Autoclave Engineers

214 Pressure Hydrometallurgy

Pressure gauge

500 mi model Figure 8.12 - ZipperClave

Figure 8.14 - Berghof autoclave

Vessel handiing devicG (optional) standard on 2 a n d 4 l i t e r m o d e l s

•m- MT i r J M ^

w

Chapter 8 - Lab Autoclaves & Pilot Plants

II

77ZZ2ZZ^ü^

fnzá

AMERICAN INSTRUMENT CO. j kcB Figure 8.15 -American Instrument Co. autoclave

215

216 Pressure Hydrometallurgy

PRESSURE CAUCE

MOTOR CONTROLLER

RÍCID

¡SSUUTION

BVLK mSULATION

SÁMPLE TUBB

uuoie

DYNA/UAC mXER

SELF ENERGIZING

SEAL

PROCESS TBERUOWELL

REATE R

AGITATOR

Pressure Products Industries, Inc.

2000 psig (138 bar) @ 350° C

300 mi, 500 mi l,2,and4UtersÍ2es.

As ihc reactor cover and body are bolicd togeiher, ihe metal sea! ring seats itself. Intemal pressure incieases the seal load and eneigizes the seal ring, assuring a tight. leak-free seal.

Figure 8.16 - Pressure Products Industries Inc. autoclave

Chapter 8 - Lab Autoclaves & Pilot Plañís 217

Packing Gland X Monitoring Nlpple

3

Coolant Channal

STIRRER ORIVE WITH SELF-SEALING PACKING GLAND

Figure 8.17 - Stirrer drive with self-sealing packing gland

218 Pressure Hydrometallurgy

High torque magnetic drives

Using high energy permanent magnets in sealed enclosures with no rotating seáis, these magnetically coupled systems elimínate the troublesome leakage problems which sometimes arise with a packing gland in severe service, permitting long continuous runs at pressures up to 30 000 kPa with little or no attention to the gland and drive. A water cooling sleeve attached to each drive protects the components from excessive temperatures arising from the reactor (Figure 8.X). The stir shaft rotates in PTFE bearings and is rigidly connected to the internal magnet. Both of these components are inside the pressure vessel. The externa! magnet is supported by all bearings and rotates outside the pressure chamber. As a result of the optimally utilized lines of forcé of the magnetic field, the internal magnet rotates in synchronization with the external magnet.

High-torque magnetic drtves

OlJter drivjng magneís

Inner magnetic rotór in a sealed housing

Inner rotor is compíeleíy encfosed wíttiin a non-roíaling housing wiiti fixed seáis.

A water-cooling jacket protects tile magneís and seáis from elevated temperalures.

Stirrer drive shaft

Figure 8.18- High-torque magnetic drives

Chapter 8 - Lab Autoclaves & Piloi Plants 219

External Driver Magnet Assembly (as seen from above) consists of an outer Steel housing that cotains four equally spaced permanent magnets with attracting poles on their inner faces.

Internal Driver Magnet Assembly is totally encapsulated. It is made up of circular, ceramic-type permanent magnets encasing a square rotor shaft and enclosed in a leak-proof housing.

In operatíon, the Driver Magnet Assembly is rotated by a motor-driven V-beIt, and the Driven Magnet Assembly rotates in response. This action drives the rotor shaft to which the agitator is connected

Figure 8.19 - MagneDrive

w

220 Presstire Hydrometallurgy

Acid digestión bombs Parr bombs

contain a Teflon cup and are available in'two sizes: 25 mi and 125 mi. They can be heated in an oven. The 125 mi bomb has a safety rupture disc built into the head which protects the bomb and the operator from the hazards of an unexpected explosión from acci-dental overloading. If the pressure in the bomb should acciacci-dentally reach the 3500 psig range, a pair of thin, frangible discs (Inconel + stainless steel) will rupture.

Berghof bomb

is a stainless steel pressure vessel with 10 mi Teflon sample holder, heated from below by a heating coil. Operating temperature up to

180°C.

Closure is effected by resilient spring member (The Zipper) inserted through a circumferential groove in body and cover. Simply reléase the safety sleeve and pulí the Zipper to remove the cover. A quick release/safety lock and cover safety device are provided to ensure that the spring is fully inserted.

Figure 8.20 - Parr acid digestión bomb

M

Chapter 8 - Lab Autoclaves & Pilot Plañís 221

Microwave acid digestión bombs are made of a microwave transpar-ent polymer which has good mechanical strength at temperatures up to 150°C, and which serves also as an excellent heat insulator for the Teñon sample cup. Since heating is developed internally within the cup, temperatures in the outer, high strength body will seldom exceed 50°C. This type of autoclave is characterized by fast diges-tión times, can opérate at temperatures up to 250°C, and pressures to 8000 kPa.

Teflon Screw (pressure indícator) Screw Cap Compressibie Disc

Bottom Píate

Figure 8.21 - Microwave acid digestión bomb

Engineering Aspects Vahes

Valves used in autoclaves have non-rotating stems to minimize leak-age. Because stem tip does not rotate on contact with body seat, the 2-piece Non-Rotating Stems designed by Autoclave Engineers elimínate the galling and scoring of stem and seat usually associated with conventional rotating stem valves (Figure 8.22). Thus, one of the major causes of valve leakage and failure is avoided.

222 Pressure Hydrometallurgy Chapter 8 - Lab Autoclaves & Pilot Plañís 223

P A C K i N G G L A N D

-L O C K I N G DEVICE

NON-ROTATiNG STEM--ADJUSTABLE PACKING-BELOW THREADS

i^W^^W

\ ^ r H

^ÉÉjMMI

^ 1

f|

l|flt|,|a ¿M^

\iw0^ _WK-'

• DESIGNER H A N D L E

ACCESSORIES

•XA

i

^{í í}

../:

STAINLESS STEEL BODY

SAFETY HEAD

NON-ROTATING STEM VALVE

Figure 8.22 - Non-rotating stem valve

Accessories

Figure 8.23 shows a safety head in which the rupture disc are in-stalled. To prevent the action of corroding vapours, the discs can be coated on one or both sides with Teflon. Such coatings and Un-ing increase the minimum rupture ratUn-ings available in a given disc.

Figure shows also a dial thermometer and a connecting tube.

3/16"

(4.76 mm) 1/2"

~ ( 1 i 7 m m ) — ^ DIAM.

FLAT SEAT RUPTURE DISC

" « r ~ ^ / ^

1/4"

-^(6.35 m m ) - ^ DIAM.

30° ANGULAR SEAT RUPTURE DISC

Discs can be coated on one or both sides wiíh Teflon. Such coatings and linings increase the mínimum rupture ratings available in a given disc

Dial Thermometer

Figure 8.23 -Accessories

224 Pressure Hydrometallurgy

DIGESTIÓN BOMB

Handle Screw Cap Pressure Spring Teflon Cap

Stainless Steel Pressure Bomb

Teflon Reaction Vessel

Regulation Range: 20°C to 220°C Cooling Chamber

HEATING MANTLE

Receptacie for Temperature Sensor Heating Coils

BERGHOF/AMERICA

Figure 8.24 - Digestión bomb and heating mantle

Chapter 8 - Lab Autoclaves & Pilot Plañís 225

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