Electrical Safety

The environment in a chemical plant is often hazardous, especially when hydrocarbons are being processed and process engineers are called upon to specify or approve the protection method for electrical apparatus installed in hazardous areas. The first prerequisite for an explosion to occur is the presence of the flammable gas – air mixture in an explosive concentration and the atmosphere in a plant can be classified into 3 zones, depending on the likelihood of the hazard being present. The risk is highest in Zone 0, where the hazard is always present. In Zone 1 the risk is lower with the hazard likely to be present under normal operating conditions. The risk is least in Zone 2 with the hazard being present only for short times due to a fault. Guidelines are available in API RP 500 for constructing the Hazardous Area Classification diagram demarcating the plant environment into different zones for various commonly encountered situations.

For Zone 0 application, the only practical option is to adopt the principle of intrinsic safety. An intrinsically safe apparatus (Ex-i) is designed and constructed such that the electrical energy carried by the circuit, even under fault conditions, is lower than the minimum ignition energy of the flammable environment in which it has to operate.

For Zone 1 application there are plenty of options to choose from. In addition to intrinsic safety, the other choices are flameproof enclosures (Ex-d), increased safety (Ex-e) and purged or pressurized enclosures (Ex-p). Flameproof enclosures do not prevent ingress of flammable mixtures from outside, but are designed to withstand an internal explosion and the flame that leaps out of the enclosure is cooled before it reaches the potentially inflammable atmosphere outside. Increased Safety design and construction ensures that there is no arcing, sparking or hot surface that can be a source of ignition. Pressurization of the enclosure by purging it with clean air or inert gas is another way of rendering it non-hazardous. For Zone 2 application, there is one more protection possibility, Ex-n which prevents ignition by avoiding sparks or hot surfaces during normal operation.

Ex-i is the highest level of protection followed by Ex-d and Ex-e. Ex-p and Ex-n constitute the lowest rungs on the ladder. The type of protection to be applied depends on the application and of course on the zone in which the application falls. Cost and maintenance are also important considerations. Ex-i is the most expensive but offers the tremendous advantage of permitting live maintenance within the hazardous area and hence it is the most widely used method of protection for process instrumentation. Ex-e is usually applied for small motors, luminaries and junction boxes. Ex-p is the least expensive option, used typically for instrument enclosures, but also the least reliable because of possible purge failure.

Ex-d enclosure design depends on the type of explosive mixtures being handled, which are divided into 4 groups – I, IIA, IIB and IIC. Ex-d enclosures for Group – IIC gases (hydrogen) require stringent design and certification making them very expensive. Depending on the Zone, Ex-e or Ex-n are often specified for motors on hydrogen service to reduce the cost. The gas groups are important only selecting the right type of flameproof enclosure and are not relevant for other types of protection.

Sankey Diagram

A picture is worth a 1000 words. Sankey Diagrams are attention grabbing flowcharts that help in quick visualisation of the distribution and losses of material and energy in a process. The width of the lines used in drawing the flowchart is proportional to the quantum of material or energy. The irish engineer Matthew Henry Phineas Riall Sankey (1853 - 1921) was the first to use the volume proportional representation of energy flows to analyse the efficiency of steam engines.

The Sankey diagram is very convenient tool to represent energy flow in any equipment or system such as boilers, fired heaters, furnaces after carrying out energy balance calculation. This diagram represents visually various outputs and losses so that energy managers can focus on finding improvements in a prioritised manner. A Sankey Diagram is also a powerful tool to sell concepts and ideas within a group and to the top management. There are many software available in the market to help construct a Sankey Diagram.

Metathesis for Propylene

Historically Propylene has been looked down upon as a byproduct of Ethylene during steam cracking of Naphtha and since Ethylene commanded a higher price, most crackers were configured to maximize the yield of the lower olefin, typically twice as much as Propylene. But this equation is fast changing. With growing applications of Polypropylene, Naphtha Crackers and Refinery FCCU’s are unable to cope up with the rising demand for Propylene. Many options to bridge this supply – demand gap are becoming attractive and one of them is Metathesis, which produces Propylene through a reaction between Ethylene and 2-butenes. Approximately 0.42 tons of Ethylene is required for every ton of Propylene.

Metathesis has been around for more than 3 decades now, but it has caught the eye only now. The first significant application of metathesis for Propylene production was designed by ABB Lummus Global and was commissioned by Lyondell Petrochemical in 1985. Lummus acquired the technology in 1997 and initiated an intense development program to optimize and broaden the technology. Earlier this month Petrochemical Corporation of Singapore’s Metathesis plant went on stream to produce 200,000 TPA Propylene. Metathesis is a term that is going to be increasingly talked about.

Catalysts & Synthesis

Technology & Flowsheet

Celebration of Chemical Engineering

The curtains came down today on IndiaChem 2006, the 3-day trade fair of the Indian Chemical Industry organised by Department of Chemicals and Petrochemicals, Government of India and Federation of Indian Chambers of Commerce and Industry. Probably for the first time we at Indian Institute of Chemical Engineers participated in a trade show of this type with the objective of popularising chemical engineering especially among the youth. Awareness of Chemical Engineering and IIChE was promoted through displays……

…………Impromptu lectures


And handouts of a CD titled ‘A Celebration of Chemical Engineering’

World Without Chemicals?

Europe, the birthplace of many a chemical and the world’s largest chemical producer today, has discovered a new hate-filled dislike for chemicals. Chemicals which impact our daily lives in products from toothbrush to condom are soon going to be treated as poisons, through a draconian provision known by the angelic acronym of REACH (Registration, Evaluation and Authorisation of Chemicals), which is poised to be adopted by the end of this year. Under REACH expected to come into force in April 2007, the onus of proving that a chemical is safe rests with the industry. This marks a paradigm shift from the present regime in which a chemical is deemed safe unless a public regulatory body proves it otherwise.

REACH would require manufacturers and traders to produce tons and tons of documentation and the Helsinki based European Chemical Agency (ECHA) will be responsible for the technical, scientific and administrative aspects of REACH. Industry is also required to withdraw chemicals that cannot be proved as benign and replace them with safer substitutes. Implementing REACH is not going to be cheap and it is estimated to cost the industry 5 million Euros over a ten year period. The prophets of doom ought to remember that the much maligned pesticide DDT saved millions of lives and was responsible for eradicating malaria from Europe and North America. A world without chemicals would not be worth living in!

Self-discipline better than being policed.

The energy intensive chemical industry is out of the ambit of mandatory energy audits, at least for another two years. That was the most important take-home on day one of the two-day seminar on energy conservation organised by Indian Chemical Council. Under the Energy Conservation Act of 2001, 15 industries had been notified as Designated Consumers, chemical industry being one of them. It is mandatory for a Designated Consumer to appoint an Energy Manager, who is expected to develop and implement an Energy Management Plan, and Energy Audit by accredited Energy Auditors was part of that plan.

The reason being doled out for a new shortened list of Designated Consumers that excludes chemical industry from it is rather flimsy. The chemical industry, it is being argued, is far too diverse and disparate to evolve easy norms for benchmarking. How a two-year moratorium will help in making that arduous task any easier is anybody’s guess. But Energy Conservation is far too important an issue to be left to bureaucratic whims and fancies. The inability of supplies to cope with the growing hunger for energy is all too evident. The investments called for are mind boggling and in the short to medium term, energy conservation is the best bet to narrow the gap between supply and demand.

The crying need of the hour for the chemical industry is to discipline itself from within and not wait for it to be policed.