Science behind Technology

Vertical Ice Condensing Technology Sublimax Technologies

The system...

There are two shell and tube heat exchangers or sublimatorsthat operate alternately.

One freezes water vapor from the process. In the other the ice is melted using hot water and then the sublimator is cooled again by injecting short bursts of ammonia liquid.

The arrangement of vertical sublimators with the ammonia separator below has a number of advantages over the oldersystem where the ammonia separator is above a pair of horizontal sublimators.

The vapor inlet duct above the top of the tubes allows vapor to spread itself evenly over the whole tube bundle.

The tubes are held in a tube sheet at the bot-tom but at the top they are fed with ammonia by individual small bore pipes so that they are free to expand.

There is plenty of room between the pipes for ice to build up without bloc-king the vapor fl ow.

Major advantages

■ Economical Lower utilities costs (electricity, steam) to give overall lower operating costs

■ Clean Very low effl uent water fl ow. No release of odors

■ Safer Lowest possible refrigerant mass. Refrigerant naturally drains by gravity back to tank

■ More Reliable Simple straightforward design with only 2 condensers

■ Fully Self Cleaning Effi cient removal of fatty matters due to the vertical design

■ More Compact Reduced fl oor space requirement

■ Top oil quality Minimized absolute pressure drop allowing the very lowest deodorizer pressure

■ Universal Suitable for any type of deodorizer or other low pressure application

Science behind Technology

Economics

The chart below shows the progress that has been madeover the years in reducing deodorizer energy. Ice condensing is the latest step in this progression.

Until the 1970’s it was common for deodorizers to have no heat recovery. The energy required for heating the oil was the biggest energy consumer. The fi rst bar on the chart shows the typical energy consumption for a deodorizer processing 20 ton/hour of oil with 200 kg/h of injection steam at 3 mbar.

The light blue represents the energy used for heating the oil, the dark blue is the injection steam and the red is the energy used by the vacuum system.

Recovering heat from the deodorized oil to heat the un-deodorized oil was the fi rst major advance. The second bar shows the effect of 80% heat recovery.

The second bar shows that in a deodorizer with conventional ejectors and heat recovery that the steam ejectors now account for the vast majority of the energyused. Many deodorizers are operating in this condition today. Rising energy costs are now forcing more and moreprocessors to consider using refrigerated vacuum equipment as a way to reduce energy consumption.

Using chilled water at 5°C to 10°C instead of normal cooling water dramatically reduces the amount of steam required for the vacuum ejectors. This is shown by the third bar. A small amount of electrical energy is required to run the refrigeration equipment but the overall energy consumption is much less.

The next step in this progression is to use a Sublimax system to freeze the condensable vapors using an ammonia refrigeration system operating at about -30°C.

An ice condensing system has about 40% of the energy use of a chilled water vacuum system and 20% of the energy consumption of a vacuum ejector set using cooling tower water. Even if electrical energy is three times more expensive than energy in the form of steam an ice condensing system has only one third of the running costs.

Ice condensing costs more to buy in the fi rst place than a conventional ejector system using normal cooling water but the operating costs are so much less that the return on investment can be very quick. The speed of payback depends on the relative costs of steam and electricity but the illustration opposite is very typical.

Schematic diagram of the improved SUBLIMAX DC system (Desmet Ballestra)

Science behind Technology

Sparge steam from deodorizer 200 kg/h

Non-condensable 10 kg/h

Operating time 8000 h/year

Steam costs $ 18/T

Waste water $ 2/m³

Electricity $ 0.05/kWh

Cooling water $ 0.05/m

On this basis the cost of running a conventional ejector set for a year is:

Steam, cooling and effl uent treatment $ 348000

The cost of running an ice condensing set is:

Electricity, steam, cooling water and effl uent treatment $ 107000

Annual saving $ 241000

Assume installed cost of ejector set $ 150000

Assume installed cost of ice condensing $ 800000

Payback time 2.7 Years

Sublimax gives extra savings compared with horizontal sublimators

Parameter Value Horizontal condenser Value Sublimax®

Sparge steam 450 kg/h

Non-condensables 15 kg/h

FFA 9 kg/h

Inlet pressure condenser 1 mbar

Ammonia temperature -35.5°C -30.5°C

Power consumption chiller 291 kW 240 kW

Power consumption NH3 pump 0 kW 11 kW

Power consumption water pump 0 kW 2 kW

Total electrical power 291 kW 253 kW

Mass ration water/air 1 kg/kg 0.6 kg/kg

Motive steam desaeration 420 kg/h 336 kg/h

Cooling water desareation 52.5 m3/h 42 m3/h

Science behind Technology

For more information on Sublimax Technology for your specifi c process,contact your local Desmet Ballestra offi ce!

Application

Refrigeration System The Sublimax System is ideally suited to working with an ammonia compression refrigeration system. Ammonia is the most effi cient refrigerant to use and the unique vertical design of the sublimators minimizes the amount of ammonia in the circuit.

If for some reason it is not possible to use ammonia on a particular site then Freon type refrigerants such as R507 can be used instead.

Most installations use compact and reliable screw compressors but it is also possible to use piston compressors which offer high effi ciency and are particularly good for lower capacity systems.

Deodorizer CapacitiesThe Sublimax System is suited to a very wide range of deodorizer capacities. The table below shows the range of capacities that can be handled with a deodorizing steam rate of 12 kg/T of oil.

Deodorizer capacity

T/day 300 600 800 1200

Sublimator surface area

m2 51 106 142 206

Deodorizer pressure

mbar 2 2 2 2

Mass fl ow sparge steam

kg/h 150 300 400 600

Gas temp. sublimator

inlet°C 80 80 80 80

Sublimax Characteristics in brief■ The ammonia fl ows down the tubes as a falling fi lm giving

improved heat transfer and a very low hold up of ammonia compared with the traditional system where the tubes are fl ooded.

■ The improved heat transfer allows the Sublimax to operate at a higher ammonia temperature compared with the horizontal system leading to lower refrigeration capital and running costs.

■ The separator can be placed directly below the sublimators to minimise piping costs or installed in a compressor room some distance away if preferred.

■ Ammonia and melt water can freely drain out of the vessels.

■ The long cycle time of at least 4 hours reduces the electrical load for cooling the standby sublimator.

Savings of annual operating costs by Sublimax® as compared toHorizontal sublimators using the same cots as above

Electricity $ 15200

Steam $ 12100

Waste water $ 1300

Cooling water $ 4200+

Total 32800 per year