GENERAL PROCESS CONSIDERATIONS IN THE SELECTION OF AGITATORS FOR SIMPLE APPLICATIONS AND IMPELLER DESIGN

Classification towards Purpose

a. Blending of miscible liquids

Easiest of agitating applications and normally axial turbine or hydrofoil impellers are preferred. Jet mixing by recirculation with an ordinary pump is equally good at lower cost

b. Dissolving

In dissolving, we want provision of high flow rate and low shear past the solid surface. Unless the solid is polymeric or sticky or viscous in nature, it is an easy operation. Data solicited are solid percentage, physical characteristics with interim changes, temp, solubility and permissible dissolving time.

c. Dispersion (liquid- liquid, solid-liquid)

Dispersion refers to mixing of non-miscible liquids or of solids in liquids, into somewhat homogeneous mass whose stability is measured by its life before reasonable separation occurs. Power input varies greatly depending on purpose and impellers generally used are pitched blade turbine, or saw tooth cutter. This is most critical of mixing problems and unless properly understood, the design is liable to fail.

d. Heat exchange

Used to speed up heat transfer by forced convection. Apparently simple but for critical applications, following data helps.

Tank dimensions and details of jacket and coils, preferably G.A.drawing.

Heat transfer co-efficients

Specific heats and thermal conductivities

Temp. of batch at start and end of cycle

Temp. – Viscosity curve of components

Whether solid suspension is included

e. Emulsification

Imparting a high power to break the molecular chains and to form the oil-water emulsion with a non-ionic surfactant. Other applications are mainly in paints & lubricants sector. Some emulsion may be steady for years and some break within minutes. Static mixers are preferred than agitators for high instantaneous power resulting better emulsion but washing pump & pipeline is problematic.

f. Solids suspension

It is simple physical (like mixing) operation but power consumption varies greatly on purpose e.g. a> complete motion of solids, b> complete suspension of solids, c> complete uniformity. Power req. is in ratio of 1: 2: 5 for said operations.

g. Chemical reaction

It can be considered as combination of blending, dissolving, heat transfer, extraction, gas dispersion, and solid suspension etc. Usually an easy task from agitator designer’s point but to be sure, pilot plant study is always recommended. A haphazard selection is vulnerable and over design (like peripheral impeller tip speed) has various detrimental effects on the final product.

h. Extraction including washing and leaching

This is normally a continuous counter- current (fluidized bed) process like solid suspension involving water to be well mixed up with other ingredients and the ingredients separates out by gravity separation. Usually of interest for mining people.

i. Gas dispersion, absorption, and stripping

Gas is impregnated from bottom as small bubbles and intimately distributed throughout the liquid usually resulting a chemical reaction. Generally curved vane impeller or multiple turbines are preferred with high speed. Fully baffled tanks should be tall and narrow in construction. Pressurized chamber accelerates the process. A better way is by static mixer employing a liquid pump and a pressurized semi- permeable solid wall to impregnate gas under pressure.

j. Crystallization

It is opposite of dissolving and is accomplished by cooling a saturated solution or by heating to drive out the solvent. The heat transfer requires a good flow. Satisfactory handling of crystals is of prime importance. Pilot plant data are desired. Generally crystals deposit at the bottom but if process deserves to be uniformly suspended, much study on the crystal structure & sensitivity is to be made for speed selection. Fluid-foil or aerofoil impellers with high flow and low shear are suggested.

NOW LET US TRY TO UNDERSTAND BASIC IMPELLER DESIGN.

As like fan (for air handling) or hydel power turbines, much research has been conducted towards agitator impeller design and it is a very wide subject with much more further scope to research and improve. Impeller is designed mainly keeping in mind the purpose or application and sometimes custom built.

The basic designs are as follows.

A. Marine Propeller

Looks like a table fan blade. Suitable for high flow and low shear e.g. blending, dissolving, heat transfer, etc. Unsuitable for solid suspension, dispersion, extraction, gas dispersion, etc. flow efficiency- 50-60%. Getting outdated but manufacturers with their old proven designs are still sticking to that.

B. Pitched Blade Turbine

Looks like a table fan blade. Suitable for high flow and low shear e.g. blending, dissolving, heat transfer, etc. Unsuitable for solid suspension, dispersion, extraction, gas dispersion, etc. flow efficiency- 50-60%. Getting outdated but manufacturers with their old proven designs are still sticking to that.

C. Hydrofoil

Hydrofoil is supposed to be a foil in water and looks like pitched blade turbine with an angled cut on the lower periphery. Its flow efficiency is better than marine propeller, replacing the later in most applications and is most desired for mixing purposes but unsuitable for high shear application.

D. Aerofoil

aerofoil is having a classic stand fan blade type look and its properties are almost like hydrofoil impellers. Of interest for mining people for mineral washing and beneficiation for energy efficiency.

E. Curved Vane

Curved Vane impeller looks like straight Pelton wheel designed to hold moving particles for some time e.g. for air absorption.

F. Stator Rotor

Old outdated design supposed to bring highest shearing action and usually specified for oil-water emulsion.

G. Saw Tooth Cutter

Saw Tooth Cutter is reasonably good for handling medium to high viscous liquids. It is most economic for emulsification. Bad design for blending simple solutions as well as handling semi solids (grease, honey etc.). Suggested for oil-water emulsion, lubricants, paints, etc.

H. Anchor

Anchor (with its namely look) is used for heat transfer from bottom or scraping viscous liquids.

I. Helical Ribbon

Helical Ribbon looking like screwed ladder or double helix model of our gene. With its diameter close to tank diameter, is used for viscosity above 80 poise.

Another very effective design for handling viscous fluid is to use pitched blade turbine placed at bottom of draft tube (equaling 70% of tank dia.) at medium speed.

IndianOil tweaks work rules for health, safety and business continuity

New Delhi, April 08, 2020

While the frontline COVID-19 fighters such as doctors, nurses, paramedical staff, and state administration services are engaged in a pitched battle with the virus, there are many more unsung heroes who are doing an equally commendable job of maintaining a constant flow of essential goods and services for communities across the nation.

Among them are those who are keeping the flame of the cooking gas 'on' in kitchens and ensuring smooth movement of the nation's wheels. These are none other than your friendly LPG delivery men, petrol pump attendants, tank-truck drivers, etc., backed by the refinery & supply/distribution personnel of the IndianOil family.

Since the commencement of the nationwide 21-day lockdown, IndianOil has put in place a comprehensive strategy to ensure the health and safety of all its stakeholders, while also ensuring business continuity.

Swift steps were taken to facilitate a work-from-home arrangement for employees in non-critical locations, through mobile communications, digital connectivity and dedicated portals. While supply locations, including refineries, pipelines, LPG bottling plants, terminals, depots and aviation fuelling stations continue to operate with optimised manpower to maintain supply of POL products.

Besides assuring millions of customers through the media and public announcements that there is no shortage of fuel supplies anywhere in the country, the Chairman, Mr. Sanjiv Singh, and other Directors have been interacting with the employees on a regular basis through video and written messages. A high-level committee headed by Mr. Ranjan Kumar Mohapatra, Director (HR), has been formed to deal with all the matters related to COVID-19, with a daily reporting mechanism not just on work assignments but also aspects of well-being of employees across the country.

As Mr. Mohapatra says, "Unprecedented times require an unprecedented response. For years, IndianOil had been using digital tools like video-conferencing to avoid unnecessary travel. The Corporation is now using this technology extensively for conducting meetings with Petroleum Ministry officials, among senior management and task-force teams, reporting channels and other office groups very effectively. It has also come in handy to keep track of the well-being of our teams working at various locations. We are pushing the envelope every day when it comes to new ways of working and remaining connected as a team spread across the country."

The Corporation is sharing important information extensively through its social media handles, besides seeking celebrity endorsements on the importance of COVID-19 precautions.

Digital technology is also being leveraged for information-sharing. For example, IndianOil's intranet portal is being used for sharing all the health advisories at one single point of access. Another digital intervention is the manner in which enquiries on life certificate of retired people are being received. Any retired person can give a life certificate, which is a self-certification done online or through an app.

At all its locations right up to petrol pumps, IndianOil has put in place an appropriate code of conduct for work, hygiene and social distancing. No event is being held that requires people to gather, and assembling of people is not allowed at any location for any purpose whatsoever. An SOP (standard operating procedure) has been developed, wherein locations are required to distribute masks and maintain hand-sanitisers at key touchpoints. At operating locations, all touchpoints such as entry gates, office work-spaces, control room machinery, and tank-truck filling areas are sanitised by spraying two or three times in a day. The Corporation has taken up in-house production of hand-sanitisers and masks wherever possible.

IndianOil has been delivering on an average of 25 lakh cylinders every day to the doorsteps of its customers for the past few days. A system has been developed at the entry of LPG bottling plants so that whenever trucks carrying empty cylinders enter the bottling plant, they are sanitised by spraying and fumigation. Proper queuing of drivers within designated markings near supply & distribution areas is being maintained to avoid clustering of people. Hand-washing facilities ensure hygiene at the main gates and canteens. Monitoring of food distribution is done and hot water is also available at canteens. Packed food as well as protective gear such as face masks, hand-wash, etc., are being arranged for tank-truck drivers.

All location personnel are briefed clearly and thoroughly on safe practices to avoid virus transmission. Hourly announcements on preventive measures against COVID-19 are made using public address systems at security gates. Flex posters at plants provide information on ways to avoid virus transmission. Thermal scanning is performed at gates for all people entering the premises. Leaflets carrying awareness information are distributed among drivers. Stay and food arrangements have been made for contract workers and migrant labour at operating sites wherever needed. Local public in areas surrounding the plants is also being advised regarding safety and hygiene issues.

Ways and means of working effectively post the current crisis are also being explored based on learnings from experiences gained from the present situation.

The Corporation has taken steps to cover petrol pump attendants, POL tank-truck drivers, packed and bulk LPG truck drivers, LPG deliverymen, DGR guards patrolling the pipeline routes, etc., at the frontline of its business under a medical insurance policy, which will also include any COVID-19 related ailments. Over 3.2 lakh people, who are a part of the extended IndianOil family, will be covered under this scheme, including the families of the insured.

Similarly, for such people manning the supply chain, IndianOil has proposed an ex-gratia COVID-19 insurance cover of Rs.5 lakhs in case of death due to COVID-19. The amount is payable to the next of kin of the deceased.

A special attendance portal has been developed for employees working from home to mark daily attendance during the lockdown period. Steps are being taken not to expose vulnerable groups such as older employees, pregnant women and those with medical conditions to front offices. Local teams are keeping in touch with families of employees who are posted elsewhere on office work and even retired employees to enquire after their health, well-being and support requirements.

The Corporation has developed an exhaustive e-learning portal "SWADHYAYA" that comprises close to 400 e-learning modules created with in-house expertise. The learning modules that can be accessed anytime on any device cover all aspects of refining, marketing and pipeline transportation in addition to topics on general management.

As Mr. Mohapatra, Director (HR), IndianOil, says, "IndianOil is looking at any and all ways to remain a learning organisation. Our employees have accessed and completed over 1.5 lakh courses during the 21-day lockdown period. We are ensuring inter-divisional movement of people at the same place to reinforce work teams and provide relief to people working in shifts. Most departments have worked out creative assignments such as updating of manuals, development of learning content, plans for the year 2020-21, etc."

John Prasad K.

Chief General Manager

Corporate Communications

Indian Oil Corporation Ltd.