April
2017

www.chemengonline.com

Filtration
Facts at Your Fingertips:
Gas Detection
Focus on Pipes, Tubes
and Fittings
Fertilizers
Safety Sensors
Cooling Towers

Perspectives
on Drying
page 36

www.chemengonline.com

April 2017

Volume 124 | no. 4

Cover Story
36

Part 1 Batch Drying with Vacuum Contact Dryers
Drying is a demanding unit operation where solvents need to be removed
without altering product chemistry. Vacuum contact dryers are essential
pieces of equipment for accomplishing this task

43

Part 2 Optimizing Analysis for Spray Drying
Precise control over spray-drying processes can be enabled
by modern measurement approaches that provide realtime
information on particle size and shape

In the News
9

Chementator
Algae printing ink has safety and sustainability benefits; Pilot project
captures rainwater for wine production; Award to lower costs
for flow-battery reactants and membranes; A quest for making
ammonia at moderate conditions; and more

16

Business News
Messer opens its largest CO2-recovery plant; Wacker expands
silicon-metal capacity at Norwegian production site; KBR awarded revamp
contract for LG Chem ethylene plant expansion; World’s largest MTO plant
starts up in China; and more

18

Newsfront The Spread of Nitrogen Fertilizers
As price margins tighten, ammonia and urea producers are diversifying theirproducts, while new catalysts and process improvements boost capacities andlower energy consumption

22

Newsfront The Future of Safety Sensors is Here Now
Wearable sensors enhance chemical plant worker safety and help close theapproaching skills gap

36

49

Technical and Practical
33

Facts at your Fingertips Gas Detection
This one-page reference provides information on major classes of gas detection
technologies and on the characteristics of several gases that may be targets ofdetection in CPI facilities

34

Technology Profile Bio-based Adipic Acid Production
from Glucose This process description outlines a catalytic approachfor making adipic acid from glucose

49

Feature Report Part 1 Crossflow Membrane Filtration
Essentials Several aspects of crossflow membrane filtration, including
process design, equipment selection and control, are detailed here

60

Feature Report Part 2 Gas-Phase Filtration Media
Properties: What to Know There are many physical properties that
can impact the ultimate performance of adsorbent media in gas-phase filtration
applications

CHEMICAL ENGINEERINGWWW.CHEMENGONLINE.COM

APRIL 2017

18

22

1

Technology Profile
Bio-based Adipic Acid Production from Glucose
By Intratec Solutions

A

dipic acid is one of the mostcommercially important aliphatic dicarboxylic acids. It
is produced on a large scale
primarily to supply the nylon 6,6 production chain. Other applications include the manufacture of coatings,
synthetic lubricants, ﬁbers, plastics,
plasticizers and polyurethane resins.

Glucose(70 wt.%)Two-stage oxidation

PhenolHydrogenation +oxidation

Cyclohexene

Hydration

Adipic acidis recycled to the hydrogen compressor. The reactor’s product stream isexpanded in a turbo generator, producing electricity. Its low-pressure
output is directed to a knock-out
drum in which a hydrogen-rich gaseous phase is recovered and recycled to the hydrogen compressor
and a liquid phase, composed mostlyof acetic acid, water and adipic acid,is directed to a crystallizer. The output from this crude crystallizer is thenﬁltered and fed to a rotary dryer to recover crude adipic acid. The motherliquor from the ﬁlter and the acetic
acid evaporated from the dryer are
mixed and fed to an extractive distillation system to remove the watercontent from the acetic acid so it
can be recycled to the hydrodeoxygenation feed mixer. Crude adipic
acid must still be dissolved in waterand then subjected to further crystallization, ﬁltering and drying to reachﬁber-grade purity.

Adipic acid production pathways
Adipic acid production has been
predominantly based on cyclohexane and, to a lesser extent, phenol.

Fermentation

Fatty acids

Oxidation +hydrodeoxygenation

Glucose

Shifts in the hydrocarbon market
and growing environmental concerns have resulted in the development of alternative production
routes for adipic acid from renewable resources, such as sugar andfatty acids (Figure 2).

Economic performance
Using data from Q3 2013, variable
costs (raw materials and utilities) for
manufacturing ﬁber-grade adipic acidfrom glucose in the U.S. are estimatedto be around $1,100/ton of product,accounting for a signiﬁcant portion of
the production costs.
This column is based on “Bio-based
Adipic Acid Production from Glucose– Cost Analysis,” a report publishedby Intratec. It can be found at: www.
intratec.us/analysis/adipic-acid-production-cost.
Q
Edited by Scott Jenkins
Editor’s note: The content for this column is supplied by Intratec Solutions LLC (Houston; www.intratec.us) and edited by
Chemical Engineering. The analyses and models presented
are prepared on the basis of publicly available and nonconfidential information. The content represents the opinionsof Intratec only. More information about the methodology for
preparing analysis can be found, along with terms of use, atwww.intratec.us/che.

Acetic acid recycle

RF

10

ST

11

CW

12

OffgasST
Acetic acid

CW

1
Air

Fuel

2

Waste
water

8

5

RF
H2
3

GlucoseQ Raw material Q Pathway Q Main product

OffgasWater recycle

Fermentation

FIGURE 2. Multiple production pathways exist for adipic acid

The process
In the process described in the following paragraphs, adipic acid is produced from glucose via a two-step
catalytic process (Figure 1).
Glucaric acid synthesis. A glucose
solution is mixed with process waterand heated before being fed to theoxidation reactor. Oxygen is supplied
to the reaction by feeding compressed
air to the bottom of the reactor. The
overhead from the reactor is fed toa knock-out drum, a liquid stream isrecycled to the reactor and most of
the recovered gaseous material is recycled to the air compressor. The reactor’s bottoms product is cooled andﬁltered, and glucaric acid is recovered
as a solid. It is then fed to rotary dryers
to remove water. Dry glucaric acid isconveyed to the hydrodeoxygenation
feed mixer.
Adipic acid synthesis. Glucaric acidis dissolved in acetic acid and heated
before being fed to the hydrodeoxygenation reactor. Glucaric acid reacts
with hydrogen at high pressure, yielding adipic acid and water. The reactor’s overhead stream, a hydrogenrich stream, is partially condensed toremove light byproducts, which areburned as fuel. The gaseous stream
Processwater

Cyclohexane

7
4

9

6

Adipicacid

Hydrogen recycle

1. Oxidation reactor
2. Air compressor
3. Rotary drier
4. Hydrogen compressor
5. Hydrodeoxygenation reactor
6. Expander
7. Crude adipic acid crystallization
8. Acetic acid recovery
9. Crude adipic acid purification
10. Refrigeration system
11. Steam boiler
12. Cooling tower
CW Cooling water
ST Steam
RF Refrigerant

FIGURE 1. The production of bio-based adipic acid from glucose via a two-step catalytic process is shown here
34

CHEMICAL ENGINEERINGWWW.CHEMENGONLINE.COM

APRIL 2017

,=E^o^eL^glhkOblnZebs^lFZm^kbZebgLbehNg]^kIk^llnk^&ahpmhlZ_^`nZk]ab`a
pressure processes@^mq&kZroblbhg
;bgFZlm^kl,=L\Zg&
Ab`aIk^llnk^Zi&
ner is the ONLY levelplications require
sensor to measure andli^\bZeho^kik^l&
map multiple points
sure protection due
and create a 3D visual
to the demandingof the topography ofprocess conditions
solids stored in silos.
bg\en]bg`ik^l&
Accounts for surfacesures up to several
variations in lump
thousand bar andmaterials, granules,
temperatures overihp]^kl%ÜZd^l%hk,))ì<pab\afZbgerh\\nkbgZnmh\eZo^l'K^eZm^]\hf&pellets for accuratepressors face similar pressures.
bgo^gmhkrOHENF>h_*mh,h_mhmZelmhk^]ohenf^'K>F;>AIK=knimnk^]bl\likhm^\moZkbhnlab`aik^llnk^Fh]^el_hkab`am^fi^kZmnk^lhkpbmaZM^Ühg\hZmbg`_hk
ikh\^ll^lZkhng]ma^phke]'Ma^rp^k^k^\^gmerZi&\ebg`rfZm^kbZel'Fnembie^l\Zgg^klrlm^fl_hkZ\\nkZ\rbg
proached by one of the leading multinational companieso^kreZk`^o^ll^el'FnembOblhglh_mpZk^fhgbmhklZeelbehl
mhikhm^\mma^bkiherf^kieZgmbg;^e`bnfZg]a^eimhpbmaZnmhfZm^]Ze^kml'FbgbfZefZbgm^gZg\^Zg]phkdlbg
bring them in line with European regulations on pressureab`a]nlm
equipment.
BinMaster
REMBE GmbH Safety + Control
ppp'[bgfZlm^k'\hf(ikh]n\ml(bg_h(-)&,]
www.rembe.de
Circle 01 on p. 78 or go to adlinks.chemengonline.com/66427-01

Circle 02 on p. 78 or go to adlinks.chemengonline.com/66427-02

Dry Screw Vacuum Pumps for Solvent HandlingLm^inimhma^ OZkb&?ehp =blmkb[nmbhgOZeo^

Customers
Internal Guide & Support
depend on
System:Mnmabeel^qi^kml
Ma^ OZkb&?ehp =blmkb&
for sizing dry
bution Valve has beenscrew vacuum
designed with a superior
pumps used ininternal guide system thatsolvent vacuum
supports the stem and discsystems. Tuthillproviding support needed
offers the SDV series with variable pitch rotors forto allow the valve to bek^]n\^]ihp^k\hglnfimbhgZg]ehp^k^qaZnlmm^fi^kZ&nl^]_hk[ZeZg\bg`Ühp'
tures. Optional PTFE internal coating is available. The
FZbgm^gZg\^?k^^Hi^kZ&
KDP series with constant pitch rotors offers simplicity andtion:reliability, along with PFA coated internals standard. You
FZgn_Z\mnk^]_khf,)-lmZbge^lllm^^eZg]NAFPieZl&\ZgmknlmMnmabeel^qi^kb^g\^Zg]dghpe^]`^mhb]^gmb_rtic, which eliminates corrosion and maintenance concerns.
b_Z]krl\k^pinfiblma^kb`am\ahb\^_hkrhnkZiieb\Z&;nlabg`Zll^f[erk^ieZ\^l^Zlber_khf^qm^kbhk%^ebfbgZm&
mbhg'Pbmabml^gobkhgf^gmZeer_kb^g]er]^lb`gZg]Mnmabeel
ing costly downtime.
complete solution offering, the decision to choose Tuthill
Positive Shutoff:
is easy.
:gbfikho^]`Zld^mlrlm^fZeehpl\hfie^m^!ihlbmbo^"
lanm&h__h_ma^pZm^klmk^Zfpbmahnmma^i^klblm^gme^Zdbg`Tuthill Vacuum & Blower Systems
associated with conventional valves.
https://www.tuthillvacuumblower.com/dam/2835.pdf
Vari-Flow Products
ppp'bg]nlmkbZe\hhebg`mhp^kl^kob\^l'\hf(oZkbÜhpoZeo^'\_f

Circle 03 on p. 78 or go to adlinks.chemengonline.com/66427-03
CHEMICAL ENGINEERINGWWW.CHEMENGONLINE.COM

Circle 04 on p. 78 or go to adlinks.chemengonline.com/66427-04

APRIL 201735

Cover Story
Part 1

Batch Drying With
Vacuum Contact Dryers
Drying is a demanding unit operation where solvents need to be removed without altering
product chemistry. Vacuum dryers are essential pieces of equipment for accomplishing this taskDrying solids is a deFilling
manding task that
Mixing/recondensing of solvents
requires both knowlEvaporation of
Evaporation ofedge of process techHeating free solvent
Coolingbound solvent
nology and a sound mechaniDischarge
cal design of the equipmentused. This article provides an FIGURE 1. Batch drying processes typically consist of the components andoverview of batch-drying prin- steps shown here
VACUUM DRYING
ciples and possible options for vertical vac- material without changing its original chemiBATCH DRYING
uum-contact dryers.
cal composition. In essence, there must be
PROCESS
Most solids in the chemical process indus- no changes to the molecular structure durEQUIPMENT OVERVIEW
tries (CPI) are recovered by precipitation or ing the drying process and no derivatives
VACUUM DRYER DESIGN crystallization. The suspended solids are me- formed due to the drying process.
chanically separated by filtering or centrifugA vacuum contact dryer is built to evapoDUST FILTER
ing in the first instance. In most solid-liquid- rate solvents from a solid by the use of theseparation processes, thermal evaporation following physical and mechanical paramSOLVENT-RECOVERYSYSTEM
does not compare favorably with mechanical eters: temperature; low pressure; and meseparation by filtration or centrifugation with chanical fluidization by agitation.
PROCESS CONTROLS
respect to energy efficiency. However, when
In most cases, vacuum contact dryers are
DRYING PROCESS STEPS it comes to the final moisture content, therrestricted by the requirement that they not
CONCLUDING REMARKS mal evaporation is often the follow-up step to influence the chemistry of the product. Howmechanical dewatering methods in order to ever, special processes are possible, where
achieve the desired dryness.
the application of high temperature will initiThe residual moisture content of the solids ate or control a chemical reaction.
after filtration or centrifugation is influenced
The degree of residual moisture in the finby the properties of the solid’s crystal struc- ished product is strictly related to the useture. A typical filtration cake can show resid- of the product and its specifications. Exual moisture content of between 5 and 45%. amples include the following: less than 5%
To dry a wet cake to lower values, thermal moisture for waste material for disposal;
evaporation is an effective way to achieve a less than 3% in foodstuffs for storage contrue “dry” solids powder.
siderations; less than 1% in herbal extracts;
For some products, continuous drying pro- and less than 0.1% in active pharmaceuticalcesses, such as belt and conveyor drying or ingredients (APIs).
spray drying, are suitable methods to achieve
A vacuum contact dryer can achieve thesea dry powder in a single pass. While continu- values for the separation of solids from solous systems are not a subject of this article, vents and there are cases where the solids,
more information can be found in Part 2 of the solvents or both, are valuable products.
this Feature Report, “Optimizing Analysis for
Spray Drying Processes” (p. 43).
Batch drying process
Almost all batch drying processes consistof the process steps mentioned in Figure 1.
Vacuum drying
During any drying process, all additives and Whether the steps are performed in a nonsolvents have to be removed from the solid agitated tray or in an agitated vessel, the conEberhard
Tritschler
Ekato Systems GmbHIN BRIEF

36

CHEMICAL ENGINEERINGWWW.CHEMENGONLINE.COM

APRIL 2017

Dust ﬁlter

Heating source

cepts discussed here for evaporation andre-condensing and collecting the solvents are
the same.
Each process step in batch drying has individual issues that require special attention:
Filling. During filling, factors such as the useof gravity or force (pumping), as well as theneed for a contamination-free transfer into
the dryer will have to be addressed.
Mixing. In order to create an even temperature and solvent-concentration distribution in the bulk material, as well as tosupport the outflow, mixing is mandatory inthe dryer. However, the influence of shear
forces created by the mixing action on thesolids needs to be addressed.
Re-condensing. Whether the purpose of
the drying is to retain the dry power anddiscard the solvent, or vice-versa, is determined by the user. Re-condensing and collection of the solvents is a demanding task
in the process.
Evaporation of free solvent. The solvent
selection dictates the evaporation conditions (enthalpy) and the maximum temperature limits of the solids dictates the thermal
limitations for the drying system.

Solvent recovery system

CIP system

Vacuum dryer

Evaporation of bound solvent. Some sol- FIGURE 2. Vacuum drying
vents tend to stick to the solid particles by systems require several
pieces of key equipment
physical bridging, or to hide in the pores ofthe particle structure, while others don’t. In
order to predict required process times, detailed knowledge of the separation behavior
is critical.
Cooling. For safe discharge, it might berequired to cool the solids to very low tem-

PROTECT PUMPS$29 25..).' s #A6)4!4)/. s "%!2).' &!),52% s /6%2,/!$
MONITOR PUMP POWER
s "EST 3ENSITIVITY
s $IGITAL $ISPLAYCOMPACT EASY MOUNTING/NLY  X  X s 3TARTER $OOR
s 0ANELs 2ACEWAY
s 7ALLTWO ADJUSTABLE SET POINTSs 2ELAY /UTPUTS
s !DJUSTABLE $ELAY 4IMERSUNIQUE RANGE FINDER SENSOR
s 7ORKS ON 7IDE RANGE OF -OTORS
s 3IMPLIlES )NSTALLATION

4-20 MILLIAMP ANALOG OUTPUT

WHY MONITOR POWER INSTEAD OF JUST AMPS?

PUMP POWER

Power is Linear-Equal Sensitivity
at Both Low and High Loads
NO LOAD

AMPS

POWER

VALVE CLOSINGPUMPING

FULL LOADVALVE OPENING

No Sensitivity
For Low Loads
NO LOADNO FLUID

FULL LOAD

CALL NOW FOR YOUR FREE 30-DAY TRIAL 888-600-3247
WWW.LOADCONTROLS.COM
Circle 18 on p. 78 or go to adlinks.chemengonline.com/66427-18
CHEMICAL ENGINEERINGWWW.CHEMENGONLINE.COM

APRIL 201737

TABLE 1. EXAMPLES FOR IDENTIFYING PROCESS LIMITATIONS
Product

Process

Solvent

Vacuumlevel

Max. temperature

Polymers

Post treatment

Water

Med. (50mbar abs)

High (300°C)

Pigments/flame
retardants

Vacuum drying

Water, organics

Med. (50mbar abs)

Average (80–100°C)

API

Post drying

Water, organics

Low (8mbar abs)

Low (40°C)

peratures prior to discharge. Since the heatremoval from a dry power is subject to evenlower heat-transfer coefficients, the coolingstep might be time consuming.
Discharge. While fluids or suspensions drain
well from a vessel, draining a dry powder can
be a challenge. Residues after draining arelost in most instances and reduce the cost
efficiency of the dryer.
In addition to the aforementioned basic requirements, supplemental codes and standards, such local laws, pressure vessel regulations, good manufacturing practice (GMP)
rules, pharmaceutical standards, U.S. Occupational Safety and Health Administration(OSHA) requirements and explosion protection measures have to be considered.

Equipment overview
The following section is intended to identify
the key components of a vacuum drying system (Figure 2).
Heat source. With respect to the heating
source for the dryer, available site utilities,
as well as product specifications have to beconsidered. While a supplier of aluminum pigments might ban water as a heating fluid forfire hazard reasons, an API producer might
avoid thermal oil to avoid contamination risks.
Both are secondary aspects, not directly related to the physical operation of heating.
The base specification for a dryer heating
system should consider the following:• Provide a sufﬁcient amount of heat
(Joules) in an energy efﬁcient way• Provide measures to keep a constanttemperature in the system
The correct heating power and capacity
calculation has to consider the following:• Initial heating of all wetted components(equipment) within a reasonable amountof time• Provide sufﬁcient energy to heat the product load to the operating temperature• Provide sufﬁcient energy to evaporate thesolvent load at the given conditions• Compensate for energy losses• Maintain temperature
In most cases, circulating a clear fluid in38

a closed loop is the appropriate method
for transporting the energy from the heatsource to the dryer vessel. For thermal fluids, water, water-glycol mixes or thermal oils
are common.
For its high specific-heat capacity, water
is the first choice as a thermal fluid when thetemperature needs to stay below 150°C. At
process temperatures above 150°C, thermal oil becomes more feasible, since oilshows only a marginal pressure rise at elevated temperatures.
Whether the closed loop is driven by one
heat exchanger for heating and one heat exchanger for cooling, or the system is fed by acentralized plant heating and cooling system
is to be decided based on the site conditions. Proper sizing is important.
Prior to any equipment selection, the physical limitations for the process need to be defined by the process owner. Each and every
process has special demands, including (butnot limited to) the three examples in Table 1.

Vacuum dryer design
The majority of commercially available vacuum contact dryers are built according to thesame principle: a jacketed vessel — either
horizontal or vertical — with a wall-wiping
agitator. Vertically oriented dryers can takeadvantage of gravity to influence productflow (Figure 3). Vertical vacuum-contact dryers include the following:• An upright cylindrical vessel with a ﬁllingto-height diameter ratio designed for bulk
mixing• A cone bottom to support the outﬂow ofsolids• A jacketed to suit the selected heating
system• A top-entry agitator, designed for solids
applications (re-starting in settled solids)• Valves and safety applications to operatea pressure vessel
Solids impellers circulate the entire contents of the vessel from the gravity filling until
the gravity discharge. The impellers can behydrofoil type, designed to create maximum
flow with the lowest possible power input.
Energy balance is important. Mixing powerby the impeller equals the power into the process. In a temperature-sensitive process, excessive mixing power input might disturb thefragile temperature balance in the product.
The key feature of all agitators in a vacuum
contact dryer is an agitator system that operates with minimum wall clearances andwipes the full wetted surface of the vessel.
Wall clearances from 5 to 15 mm are common and feasible, and require both a pre-CHEMICAL ENGINEERINGWWW.CHEMENGONLINE.COM

APRIL 2017

cisely fabricated vessel and a deflection-free balanced impeller.
Since the process is typically operated
under vacuum, the vessel must be fabricated according to the American Societyof Mechanical Engineers (ASME) Boiler
and Pressure Vessel Code (BPVC), andmust also follow local laws and regulations, as applicable.

Dust filter
By heating a wet solid in the closed
vessel, evaporation will start. The solvents will be condensed in an externalsolvent-recovery system. This migrationof solvents will create a strong gas flowthat may cause dust formation as thesolids dry.
Commercially available solvent-recovery systems are built for heavy duty
services, but not for high amounts ofdust. In order to prevent the plugging
of lines — or simply to keep the solids
where they belong, in the dryer vessel— a dust filter is installed on top of thedryer vessel.
Modern dryers feature heated filter
domes with automatic blowback clean-ing systems that are properly designed
to protect the solvent-recovery systemfrom the dust.
Two types of commercially available
filter elements are discussed here, butothers’ experience might include many
more systems.
The dust-loaded area of the dryer isseparated from the solvent recovery line
by a gas-tight filter plate. This filter plate
carries the filter elements. One possibility is a fabric bag filter mounted on awire cage, while the other is a sinteredmetal or wire mesh (10 μm) cartridge
made of metal wire or metal fibers
The selection of one of these filter
systems is based on owner preference
and on the overall operating conditions(including temperature). While the fabricbag filters are disposable and low in replacement cost, the metal cartridge is reuseable with a high lifetime expectation.
In both cases, proper sizing of the filter
is critical. An undersized filter will lead toan excess pressure drop in the solventrecovery line, with effects on the total
evaporation regime.

FIGURE 3. Vertical solids dryers cantake advantage of gravitational forces forsolids flow

&DOO
WKH([SHUWVIRUDOO\RXUVROLGVSURFHVVLQJ
6ROLGV0L[LQJ
5LEERQ &RQH%OHQGHUV)OXLGL]LQJ0L[HUV
6LJPD%ODGH0L[HUV$SSOLFDWLRQV
$3,VÂ$J&KHPLFDOV%LRORJLFVÂ&DWDO\VWV DOVRIRUKLJKYLVFRVLW\PL[LQJ&HUDPLFVÂ&KHPLFDOV

6L]H5HGXFWLRQ)RRG,QJUHGLHQWV

:HW 'U\6L]H5HGXFWLRQ+HUELFLGHVÂ0LQHUDOV

6WHHO &HUDPLF/LQHG0LOOV

1XWUDFHXWLFDOVÂ3HVWLFLGHV-DUV -DU5ROOLQJ0LOOV

3KDUPDFHXWLFDOVÂ3LJPHQWV

9DFXXP'U\LQJ

3RO\PHUVÂ3RZGHUHG0HWDOV'U\HUV &RPSOHWH6\VWHPV

3URWHLQVÂ5HVLQVÂ9LWDPLQV

Q
UA
EXCELLENCE
I
T
Y






4XDOLW\,QQRYDWLRQ6LQFH®

C O R P O R AT I O N
Environmentally Safe VpCI ®/MCI ® Technologies

ZZZSDXORDEEHFRPVDOHV#SDXORDEEHFRP
Circle 20 on p. 78 or go to adlinks.chemengonline.com/66427-20
CHEMICAL ENGINEERINGWWW.CHEMENGONLINE.COM

Circle 07 on p. 78 or go to adlinks.chemengonline.com/66427-07

APRIL 201739

TABLE 2. TYPICAL EVAPORATION TEMPERATURES FOR WATER
Water

Pressure, mbar abs

Boiling temperature, °C

1,013

100

100

45

10

5

TABLE 3. TYPICAL EVAPORATION TEMPERATURES FOR ETHANOL
EthanolPressure, mbar abs

Boiling temperature, °C

1,013

82

100

32

10

5

TABLE 4. TYPICAL DRYING BEHAVIORS
SystemStep 1

Step 2

Step 3

Pigment drying

Evaporate surface
moisture

Transition

Evaporate crystal
moisture bound in thecapillary

Comment

High solvent load, lowdust emission

Dust emission starts

Long duration, lowsolvent load, dust
formation

Solvent-recovery system

FIGURE 4. The solvent-recovery system recondenses thesolvents as the dryer evaporates them40

As the vacuum contact dryer evaporates
the solvents, the solvent-recovery systemneeds to re-condense the solvent, usuallyat the same rate. There are many ways toachieve this objective. This article covers one
method that has shown some advantages
when it comes to collecting the solvent for
further use (Figure 4).
A robust vacuum pump (liquid-ring pumpor dry-running pump) creates the initial low
pressure that will activate the process. Design
criteria for the pump includes the following:• Evacuate the total system volume in areasonable time
• Maintain the vacuum level under changing
process conditions• Compensate for air leakage across the fullsystem• Compensate for inert gas volumes introduced during the process
In essence, the vacuum pump has tokeep the system running while also covering
for losses.
The key component of the solvent-recovery system is the heat exchanger or condenser that is installed on the low-vacuumside of the pump. Properly designed andactivated with the proper cooling fluid, solvents evaporated in the hot dryer vessel will
migrate to the cold surface of the heat exchanger and will be re-condensed.
Condensation on the vacuum side of thepump will result in a huge draft — the condenser acts as a “vacuum pump.” The liquefied solvents are collected in a collection
vessel for further use or transfer. Cooling or

insulating the vessel is recommended when
the system is installed at higher ambient
temperatures.
With respect to the cooling methods,
again the circulation of a clear fluid is one of
the first choices. Based on commonly usedsolvents and the vacuum level achieved,
anything from water (at 8°C) to brine (at–15°C) might be required. One item needs
to be considered: water at 25°C should not
be considered “cold.”
Collecting the solvents is the most precise
method for back-calculating the residual
moisture in the dry product. This can bedone simply by measuring the solvent volume. A small amount of solvents, however,might escape even a properly designed condenser. To catch the saturated solvents, asecond condenser in the exhaust line of thevacuum pump might be required.

Process controls
All of the components mentioned in this article require safe and precise operation. The
large number of signals to be processed andvalves to be handled does not allow manual
operation of such a system, except situations involving small-scale tests in a laboratory environment. Automatic process control
systems that focus on a proper temperatureand vacuum regime are mandatory for industrial vacuum drying.

Drying process steps
As noted earlier in the article, an effective
drying process requires knowledge of the full
picture of the process, including filling, mixing, re-condensing, evaporation of free solvent, evaporation of bound solvent, coolingand discharge of products
Filling. There are many ways of transferring asolvent-loaded wet cake into a dryer vessel.
This could be the subject of an article on its
own, covering all aspects such as contamination, operator exposure levels, explosion
risks and dosing the correct amount. Some
dryers provide a wide opening at the top of
the dryer vessel where valves, dosing or conveying systems, including (but not limited to)material-containment apparatus, can be installed. Gravity will support the filling process.
Mixing. During the filling process, the mixer
may or may not run. However, it has to be
designed for re-starting in settled solids at
any time during the process. Stalling during a drying process should be avoided. In
some rare cases, however, stopping the agitator is even required to overcome a certain
process condition. In essence, an “off-theshelf” agitator will not do the job. Dryer agi-

CHEMICAL ENGINEERINGWWW.CHEMENGONLINE.COM

APRIL 2017

ing the dry solids will consume additional
production time. In addition, the stainless-steel mass of the dryer equipment
also needs to be cooled. In cases wheretime is of the essence, it might be beneficial to separate the functions and transfer
the hot solids by closed pipe into a designated cooling vessel directly below thedryer. This procedure saves the energy
required to cool the equipment mass.
Maximum yield after discharge is important for the cost balance of the drying
system. In a single-product manufacturing process, leaving residues in the drying
vessel for the next batch may be permitted. However, in a typical pharmaceuticalor fine chemicals process, “cross-contamination” of products is banned.
With a cleverly designed vessel and aflexible agitator, the equipment can bemade to suit the flow characteristics of the
product. A vertical vessel will, by nature,drain better than a horizontal drying vessel.
A cone bottom supports outflow far better
than a flat or dished bottom. The agitator
must be in a position to rotate at elevatedspeeds, including the changing the direction of rotation for discharge. Also, surface
polishing and surface linings can help toreduce friction as the solid product flows.
Scaleup. Scaling up a drying process
requires both small-scale testing capabilities and scaleup experience. Once
successfully dried at a 25-, 50- or 100-L
scale, scaleup rules can be used to predict the following:• Drying time
• Solvent load, energy demand• Residues after discharge• Particle size changes due to shear on
the product• Wear of the agitator parts due to exposure to the productAs a basic rule, a safe scaleup requiresthat the geometry of the small-scale testdryer is geometrically similar to the production-size dryer.
Scaleup works best when the trials
have been carried out under identicalphysical parameters (such as pressure
and temperature) as the full-scale process. If this is not possible, correction
factors have to be applied to the scaleup
formula. The scaleup rules consider thefollowing items:• The ratio of volume-to-heated-surfacearea of the small-scale dryer to thefull-scale dryer• A temperature correction factor inmoving from small scale to full scale, if
42

the values deviate from one another• A factor to account for the inﬂuence of
agitation speed on the evaporation
If all data are available, safe scaleup by
a factor of 200 is readily achievable.

Concluding remarks
The information included here describes
the basic concept of a vacuum contactdrying system. This type of system canbe applied to many chemical applications by designing the components accordingly. The following are some of thetypical situations:• Selection of wetted parts with respect
to corrosion (most commercially available metals)• Designing the components for GMP
standards (food and pharmaceuticalindustries)• Designing the components for criticalsolvents, such as organic solvents• Designing the components for severesite conditions (outdoor and weather
protected)• Designing the components for highdemands on cleanability (cleanroom
environment)• Designing liquid cleaning systems(clean-in-place; CIP) for the dryer vessel• Designing the components for out-ofspeciﬁcation applications (high temperatures and pressures)
Aside from plant experience and knowledge of the process, cooperation with a capable dryer company opens a wide rangeof possibilities beyond vacuum contact drying. Applications include solvent extraction
from herbs and spices; all-in-one reaction
systems for paints and pigments; food pasteurization and drying; and all-in-one chemical reactor/dryers.
Q
Edited by Scott Jenkins

AuthorEberhard Tritschler is product manager
for sales at Ekato Systems GmbH (Käppelemattweg 2, 79650 Schopfheim, Germany; Phone: +49 7622-6907-808;
Email: eberhard.tritschler@ekato.com;
Website: www.ekato.com). Tritschler has
served in sales and application engineering at Ekato Systems since 2005, andprior to that, worked in sales and application engineering at several other Ekato
divisions. Tritschler holds a bachelor's degree in mechanicalengineering from the Technical School of Engineering in Lörrach Germany, and has also earned a degree in business administration from the HWK School in Schopfheim, Germany.
Aside from his day-to-day business duties in the sales organization of Ekato Systems, Tritschler also speaks at customer
seminars, tradeshows and business schools. He has special
expertise in the mechanical aspects of vacuum contact drying,as well as extractions and all-in-one reactions in batch-type
mixing vessels.

CHEMICAL ENGINEERINGWWW.CHEMENGONLINE.COM

APRIL 2017

Solids Processing 2017 Special Advertising Section

Continuous cleanroom pastillation
Sandvik’s Rotoform pastillation system is available in GMP
versions for pharma, cosmetic and food applications

A

trically around the stator. Product droplets
are deposited onto a stainless steel belt.
Indirect cooling via the endless steel
belt eliminates any risk of cross-contamination between product and cooling water,while a hot-water-based belt cleaning system eliminates the risk of cross-contamination between batches.
All working parts that can come into contact with the product are stainless steel foreasy cleaning and maximum hygiene. The
structural materials have a very low surface
roughness. All components (i.e. gaskets) inside the Rotoform are made from materials
compatible with the respective product.
The whole machine is covered withhoods, with an extractor fan to avoid pollution of ambient air. The control system is
supported by cameras that transmit images
to an outside terminal.
The Sandvik Rotoform system is widelyused across the food, cosmetic and pharmaceutical industries for products such as
chocolate, lipstick and suppository mass.
www.processsystems.sandvik.com

chieving a successful pharmaceutical
audit for cleanroom pastillation requires
a GMP-compliant production unit with professional documentation. The Sandvik
Rotoform granulation system meets thisUniform pastillation thanks to Rotoform
requirement and converts liquid melts into
solid pastilles.
Every aspect of the Rotoform system has
been designed to ensure GMP compliance.
All piping connections are quick-release
types for easy cleaning, and the Rotoform is
powered by a maintenance-free drive belt.
Rotoform uses a heated cylindrical stator supplied with liquid product, and aperforated rotating shell that turns concen-

Industry events for solids handling

PHOTO: © MESSE DÜSSELDORF/CONSTANZE TILLMANN

and packaging to the chemical process industries. Below is a short calendar of themost important of these events in the U.S.
and Europe this year:

Packaging in action at interpackAlarge number of dedicated exhibitions,conferences and training sessions
shows the importance of solids handling

CHEMICAL ENGINEERING

May 4–10, 2017
interpack 2017
Messe Dusseldorf, Düsseldorf, Germany
May 10–11, 2017
SOLIDS Dortmund
Messe Westfalenhallen Dortmund, Germany
May 16–18, 2017
Toronto Powder & Bulk Solids
Toronto Congress Centre, Ont., Canada
June 19–21, 2017
Eurodrying 2017 – European Drying
Conference
University of Liège, Liège, Belgium
September 14, 2017
Bulk Solids Handling Workshop
organized by Chemical Engineering
Sky Philadelphia, Pa., U.S.
September 26–28, 2017
POWTECH 2017
Exhibition Centre Nuremberg, Germany
September 27–29, 2017
The 2017 Powder Show & ConferenceGreater Columbus Convention Center,
Columbus, Ohio, U.S.
October 4–5, 2017
SOLIDS Rotterdam 2017
Ahoy Rotterdam, Rotterdam, Netherlands.

WWW.CHEMENGONLINE.COM

APRIL 2017

A small footprint
takes a big step
EKATO’s new lab dryers are
flexible and versatile

E

KATO SYSTEMS Germany is promoting a
range of “desktop-type” laboratory-scale
dryers. With working volumes of 3–6 l, the
VPT3 dryers cater to a growing demand fordrying tests in vertical apparatus, and also
allow small batches of product to be manufactured. Scale-up is easy because the design matches EKATO’s
full-scale dryers.
The base modelin this plug-and-playsystem is a drying
vessel with a water
jacket for heatingor cooling. The variable-speed motor accepts both the EKATOPARAVISC impeller
for free-flowing solids
and the EKATO ISOPAS
impeller for pasty
products.
Working pressures range from
–1 to +2 bar g.
Vacuum is provided by a membrane vacuum
pump with condenser and condensate vessel.
Working temperature is up to 131°C.
Contact parts
EKATO VPT3 laboratory
are made fromdryers handle bothstainless steel,free-flowing and pasty
with other mamaterials, and are ideal
terials available
for process development
on request.
Control is
via a touch screen, with an electric motor
used to lift the vessel lid. A data logger andan interface for remote data transfer areavailable on request.
Just like EKATO’s production-scale dryers, the VPT3 dryers can handle thick pastelike products just as easily as low-viscosity
suspensions. For shear-sensitive active
ingredients that require gentle drying, the
EKATO PARAVISC impeller combines uniform product circulation with good heattransfer. Varying the shaft speed allows experimenters to find the operating point that
reliably achieves the shortest drying times
or the best product properties. A rental unit
is available.
www.ekato.com

75