IChemE SYMPOSIUM SERIES NO. 153 # 2007 IChemE

INHERENT SAFETY THROUGH INTENSIVE STRUCTURED PROCESSING:THE IMPULSE PROJECT

Parastoo Khoshabi1 and Paul. N. Sharratt2

1e-mail: Parastoo.khoshabi@postgrad.manchester.ac.uk2e-mail: paul.sharratt@manchester.ac.uk

Safety, health and environmental (SHE) issues are important factors that need to be taken into

account in any process and ultimately plant in order to avoid or minimize any harm to employees

and environment. The main aim of the “IMPULSE”� project is to innovate through targeted appli-

cation of structured processing equipment such as microreactors, compact heat exchangers and thin

film devices. Substitution of batch plant by continuous plant in pharmaceutical and fine chemical

plant is another aim. There is expected to be a considerable difference between the safety, health

and environmental performance of traditional and “IMPULSE” plants. In this paper an initial com-

parison of hazard issues in batch and IMPULSE continuous (IC) plant is made, and the methods

used to analyse the situation are discussed. The comparison of conventional and IC plant is con-

sidered for the hydrogenation process as case study in terms of SHE (safety, health and environ-

ment) issues. While in the IMPULSE plant major releases and hazards are clearly less likely for

IC, the potential for operator exposure and minor problems may be greater. It is concluded that

further work is required to assess the overall balance of changes in SHE performance to be able

to inform designers.

KEYWORDS: inherent safety, environment, IMPULSE, process intensification

“in a healthy society, engineering design gets

smarter and smarter; in gangster states it gets

bigger and bigger”

Peter Beckman

INTRODUCTIONIf a system remains non-hazardous when subject to alldeviations that might lead to danger, the system is calledinherently safe. According to (Kletz 1998) this arises fromdesigning a safe plant and not by adding equipment to thesystem to make it safe. This can be achieved by preventingproblems at their root causes; therefore inherent safety hasan important role during process design.

Nowadays, industries are looking for shorter leadtimes, higher quality for their products as well as lowerenvironmental discharges and safer plant. It has beensuggested that in order for the chemical industry tosurvive in the developed world, radical and novelapproaches are needed. The main aim of the IMPULSEProject (Integrated Process Units with Locally StructuredElements) is to innovate through application of structuredprocess equipment such as microreactors, compact heatexchangers and thin film device (Sharratt, Matlosz andBayer 2006). Substitution of batch by continuous plant inpharmaceutical and fine chemical plants is another aim.The IMPULSE approach is application driven – in otherwords the novel devices being deployed with the aim ofdelivering the best possible process outcome; this is distinctfrom the early approaches of Process Intensification where

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the target was equipment size, not business success. Inthis context, business benefit is taken to include safety andenvironmental performance.

The novel, IMPULSE devices will be smaller com-pared to conventional devices. There should be a consider-able difference between traditional and IMPULSEtechnologies in terms of fire and explosion risks, harmfulemissions and efficiency. In order to find out whether, andin what ways IMPULSE continuous plant is inherentlysafer than batch, a comprehensive assessment is required.

Green chemistry has also emerged as a response togrowing public fear of chemicals and the chemical industry.Green chemistry is the design of substances and processesthat eliminate the use and generation of hazardous material.Green chemistry is a central approach to pollution preven-tion and seeks to introduce innovative scientific solutionsto the environmental problem. Anastas and Warner (1998)provide 12 principles for green chemistry, which includerequirements for the avoidance of hazardous substance,materials and energy efficiency and reduction of accidentpotential.

A main strategy in developing inherently safer chemi-cal process is process intensification. Reduction of inventoryof hazardous substances or energy leads to reduction of theconsequences of failure to control that hazardous substance(Barton and Rogers 1993). Safety of a plant should be basedon reduction of possible damage. Safety devices are notperfect and will probably fail at some point; they are nottotally reliable. In a chemical plant with large content ofhazardous material or energy, the result of the failure ofthe add-on safety devices can be large. In a small plant theinherent capability to cause damage is reduced, so small

�www.impulse-project.net IMPULSE is an EU Framework 6 Integrated

Project for the deployment of novel “structured” processing devices.

IChemE SYMPOSIUM SERIES NO. 153 # 2007 IChemE

plant can be considered safer (Stankiewicz and Moulijn2004). Nevertheless, there is also a need to reduce prob-ability of hazards as much as possible – it is possible thatthe increased complexity of small plant might result inmore frequent problems and therefore increased risk.

In order to support comparison of the IMPULSE con-tinuous (IC) plant with conventional plant the main Safety,Health and Environmental issues for a typical Pharma-ceutical plant are listed in Table 1. This table also summar-ises existing understanding of the means to assess thecorresponding risk for IC plant, or equally identifies gaps.

INHERENT SAFETY AND IMPULSEIt is important to find the best choice of technology in orderto apply in a system. Choosing between IC and conventional

Table 1. Major SHE hazards in pr

Hazards in

pharmaceutical

plants (batch) Due to

Runaway reaction † Loss of reactor

cooling or agitation during

an exothermic reaction

Reactor over

-pressurization

† Overcharging with

compressed gas or liquid

† Excessive vapour generation

Fire and explosion † Due to handling flammable

solvent or finely

divided organic powders.

Dust explosion † Size of PM� ,75

microns form

exposure mixture in air.

† Lower explosive

limit 15–60 gm m23

† Upper explosive

limit 2–6 kg m23

† Secondary dust explosions

which come from the ignition

of very large dust clouds

have the most severe

consequences

Occupational

health

† Due to uncontrolled exposure

to harmful substances.

† Due to exposure to harmful

physical conditions

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batch manufacturing methods requires deep consideration.IMPULSE is trying to achieve inherent safety through oneor more of

. having all equipment as small and safe as possible

. allowing substitution of dangerous materials with lessdangerous by being able to process them in ways notpossible in traditional plant

. attenuation of the operating conditions and

. intensifying the process to minimise inventories.

To move beyond the simple argument that “smaller isbetter” needs a more detailed analysis. Reasons for havinglarge reactors are low conversion and slow reaction orboth. If the conversion is low, reactants should be recoveredor recycled which leads to increasing inventory, particularly

imary pharmaceutical manufacture

Protection

approaches

IC plant issues/risk assessment

† Emergency venting

† Containment

† Crash cooling

† Reaction inhibition

Lower because of

lower inventory

† Adopting suitable

operating procedures.

† Using relief pressure valve

Lower risk as devices

can withstand

higher pressure, also

lower storage of

pressure energy in

smaller devices

† Testing the materials

used for fire and

explosion potential

† Safe process design

(considering key factors

such as gas and vapour

limits, flammable and highly

flammable liquids, finely

divided powders and dusts)

Lower risk because of

lower inventory and

stronger device

† Eliminate potential

ignition sources

† Adequate earthling of metal

conductors and

electrostatic charges

† Explosion venting, inerting

suppression and containment

Not clear

† Containment, PPE,

automation

Not clear, but more

complex plant with

more joints may

be a concern

IChemE SYMPOSIUM SERIES NO. 153 # 2007 IChemE

in batch reactions. In continuous plant it will tend to lead toadditional plant items to carry out the separations, withadditional opportunities for leakage. While acceleration ofreaction by catalysis or higher temperature/pressure arepossible there are problems. Development of catalyticsystems is expensive and difficult, especially where the reac-tion is not one of the set of commonly catalysed reactions(such as hydrogenation). While running under moreextreme conditions can reduce reactor volume substantially,there is a trade-off of increasing the hazard per mass ofprocess fluid, as well as increasing the likelihood of cor-rosion. In general, plants with vapour phase processingwill have lower inventories than liquid phase processes,but this is rarely feasible for pharmaceutical processes thathave large, thermally sensitive molecules of low vapourpressure.

Clearly, some types of hazard are much reduced bymoving to intensive, continuous processing. For example,in a semi batch reactor in operation one or more reactantis in the reactor and the last reactant can be added duringthe progress of reaction. As the process progresses, theaccumulation of unreacted material can happen due tofailure of the mixing process or exhaustion of the catalysts.In general, even at high pressure and temperature a smallreactor is safe as it has little material and in the extremecase of loss of all material, it is still nearly impossible tohave a serious incident.

Issues that need to be engineered in order to controlhazards in IMPULSE plants include:

. Equipment is smaller in size but maybe more in number

. More sophisticated to operate / more complex, soadditional concerns around control reliability

. Higher probability of failure of some devices – forexample microreactors often have very thin internalwalls that may be less thick than a typical corrosionallowance in a standard plant item

. There may be more connections (and potentially moreleaks)

. Under more severe operating conditions devices may bemore prone to blockage, failure

. More maintenance may be required.

By contrast, advantages are as follows:

. Smaller inventory

. Larger surface area belongs to small plant; therefore,additional cooling capacity is not required.

. They can be built in whole or part off-site at specialistworkshops, allowing higher engineering standards tobe delivered easily.

. Devices can be passive (i.e., no moving parts like agita-tors ) so IC can be more reliable

. Greater heat loss/ cooling capacity

. Physically stronger

. Lower accumulation.

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METHODThe IMPULSE project is developing a number of industrialcase studies in applications in a range of industry sectors –and by the end of the project all of these will be assessed fortheir SHE and Sustainability performance. The workreported here concentrates on the application to pharma-ceutical production, and in particular hydrogenation. Inorder to understand the scope and nature of real industrialissues and concerns and to investigate the current hazardissues and what would change with an equivalent IC plantthe following approach has been adopted.

. Survey of safety issues for an existing hydrogenation(questionnaire) for IMPULSE partners, including identi-fication of concerns in moving to IC plant (Case StudyA);

. Consideration of a specific hydrogenation process (bothan exisiting batch process and an IC equivalent) (CaseStudy B);

. Gap analysis to identify areas for further analysis;

. Generation of further research targets to fill the ident-ified gaps.

In this paper, the first two are addressed.

CASE STUDY AIn order to have a better understanding of the hazards a surveywas carried out at one of the companies participating inIMPULSE which operates a range of batch chemicals pro-cesses, including hydrogenation. The questions weredivided into 7 sections such as training, cost, monitoring,hazards, storage and handling of H2. The questions were putto the technologists responsible for the technical support ofan operating multi-purpose hydrogenation unit in the UK.

The company’s response to the questionnaireindicated that in order to achieve a safe plant variousdifferent hazard identification approaches are used, such asCOSHH, studies based on the 6-stage ICI hazard assessmentsystem, COSHH assessment, manual handling assessment.More detailed studies are done by third parties such as con-tractors/consultants.

It was concluded that in the hydrogenation plant manysafety precautions are taken and safety assessment delivers ahigh level of performance. Their major worry is about thenature of hydrogen. As it is highly flammable they believedthat reducing the inventory would certainly reduce thehazards and capital cost. However, they also believe thatthe novel technology has its own problems. For example,the need for reactors with wide processing capability isone of the main concerns. In addition the presence of impu-rities might be a big driver in novel technology so getting ridof impurity is another substantial concern. Whether movingfrom conventional plant to novel plant is cost effective ornot is another concern; as usual money is important. It isimportant for the people who invest for it to know the costeffectiveness of moving from conventional plant to theIMPULSE plant. SHE issues might be a big driver forH2. The risk most probably will change in IMPULSEplant – for example the pressure in the conventional plant

IChemE SYMPOSIUM SERIES NO. 153 # 2007 IChemE

is not a concern because pressure in the conventional planttends to be near atmospheric pressure. By contrast, pressureis a main concern in novel plant. The leakage from valvesand flanges might not be a concern in novel technologythough leakage from pumps might be as the numbers ofpumps are more in novel plant compared to the conventionalplant. It seems that in order to satisfy the plant technologiststhat the novel technology is safe, more evidence required.

CASE STUDY BA hydrogenation process operated by another IMPULSEpartner was considered. This hydrogenation step is onestage in a longer synthetic chain. Initially, a comparisonwas made of all safety issues for the exisiting process andan outline design for an IC hydrogenation process. Here,an attempt was made to develop a side-by-side comparisonof all of the safety issues in the two types of plant. Anexcerpt of the results is given in Table 2.

It can be seen from Table 2 even at this stage that ourknowledge of the detailed design of the IC plant is not

Table 2. Excerpt of comparison of equipment hazards in C

Issues/features

Current

process IC

Manhole Yes No

Leakage of H2

from flanges

Yes Probably small flanges

are involved and

may have more

Leakage of N2

(used for inerting)

Yes Probably fewer flanges

will be used so the

leakage is lower,

possible that inerting

not needed

Exothermic

reaction

Yes Less likely and very

small inventory

Existence of

solvent storage

Yes ?

Pressure 45 psi High p

Number of flanges 25 ?

Existence of

agitator

Yes Probably not

Existence of

ventilation system

Yes Hydrogenation would be

in a well-vented place

Quality of construction – It may change e.g. due

to corrosion a better

alloy and protection

layer is needed.

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sufficient; for example there is no information aboutpossible changes to the operation temperature, pressureand so on. However, just using common sense it can befound out that the hazards of having runaway reaction isless due to having less inventory, the possibility of humanerror may be less due to using computers rather than relyon humans. Furthermore, the possibility of injury to employ-ees is low due to not having the operators around the systemcontinuously. The operator most probably would be in acontrol room and controlling the system. Thus, in case ofhaving explosion (which in any case would be small dueto low inventory) the operator is away from the system sothe risk of injury is much reduced.

CONCLUSION AND FUTURE WORKWhile major releases and hazards are clearly less likely forIC, the potential for operator exposure and minor problemsmay be greater – more work is needed to resolve this.Also, as the IC plants are going to be compact comparedto conventional plant so this technology probably requires

ase Study B hydrogenation process and assumed IC process

Hazard concerns

related to these issues

in Case Study B

Hazard concerns

related to these

issues in IC plant

Operator exposure

in inspection

None

Fire and explosion due to

high amount of leakage

Lower inventory,

reduction of leak rate,

but possibly more leaks

Operator suffocation Eliminated?

Explosion Lower volume (less energy)

Flammable Probably still required

– P is great but V is less

and E ¼ PV So released

energy is small

Having higher leakage Probably less leakage,

though the number of

pumps might be more

than conventional plant

Breaking the agitator Maybe or having kind of

rotating disks

Failure of

ventilation system

Need to consider ventilation

in smaller, tighter plant

– Corrosion

IChemE SYMPOSIUM SERIES NO. 153 # 2007 IChemE

new identification and qualification methods; all of themethods found in the literature are for conventional plantwith significant spacing between plant items. As IC plantis smaller it might be possible to use energy integrationand possibly even renewable energy sources. Anothertheme that has emerged is the relation between size ofplant and risk, as well as how this risk changes in movingfrom traditional batch to IC plant.

REFERENCESBarton, J. and R. Rogers (1993). Chemical reaction hazards,

Institution of chemical engineering, Rugby, UK.

Hendershot, D. C. (2006). “An overview of inherently safer

design.” Process safety progress 25(2): 98–107.

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Khan, F. I. and P. R. Amyotte (2004). “Integrated inherent

safety index (I2SI): A tool for inherent safety evaluation.”

Process safety progress 23(2): 136–148.

Kletz, T. A. (1998). Process plants: a handbook for

inherently safer design, Philadelphia, Pa.; London: Taylor

& Francis.

Sharratt, P. N., M. Matlosz and Bayer T. (2006). IMPULSE- the

challenges in adopting a new processing paradigm. CHISA,

Prague, Czech republic.

Stankiewicz, A. J. and J. A. Moulijn (2004). Re-engineering

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Inc.