   |
The annual world trade in fertilisers in the mid-1990s amounted to approximately
120 million tonnes, which represented around 8% of all sea-borne bulk trade.
The international fertiliser trade is a huge industry, which ranks fourth
after coal, iron, and grain in terms of value.
The various steps involved in the manufacture of finished fertiliser
products, from raw materials through intermediate products, are shown below.
AESSEAL plc have formed an alliance with a number of fertilizer manufactures
with the common goal of reducing seal failures and increasing up time. Traditionally
two main seal support methods are used in this industry when sealing slurries
and or the chemicals associated with fertilizer manufacture, which within
themselves have been identified as large volume water consumers whilst not
providing the anticipated seal life. These two methods are indeed again
the quench to drain method (API Plan 62), and the flush method (API Plan
32).
As previously discussed, these seal support methods have major limitations
in normal process industries, however, using seals when pumping fertiliser
constituents brings additional sealing challenges.
For example, Phosphoric Acid and pond water are less than desirable liquids
to seal as compared to cold drinking water. Mechanical seal faces do not
like heat nor do they like dirt and solids. When phosphoric acid is being
sealed at normal process temperatures it does provide minimum lubricating
qualities for the faces. The problem is that as the process changes so does
the acid providing the film on which the mechanical seal faces run. If the
acid gets too hot it will vaporise and when the temperature is too low the
solids in the acid can come out of suspension. Both of these conditions
will create adverse face conditions and greatly reduce the reliability needed
to seal Phosphoric Acid.
Pond water is more difficult to seal than is Phosphoric Acid. Hot pond
water is aggressive in nature, and due to its chemical make up it grows
crystals that are very abrasive. Pond water does not provide the seal faces
with any lubricating qualities, short or long term. Film stability is compromised
here as well.
In the past, packing and single seals with high-pressure flushes have
given the ability to run mechanical seals with a limited degree of success.
The price paid for this success is shortened seal life, dilution of the
acid strength, higher energy costs to drive off the water in the evaporation
process and the continuous flow of water being added to the pond water system.
All of these issues give way to higher plant operating costs.
The costs associated with water being added to the process are very high.
The evaporation costs can be around £0.15 ($0.27/€0.22) per litre
per hour (£0.55 / $1.00 / €0.83 per gallon per hour). Water to
ground costs are very high as well. If the plant is in the liming process,
the costs are considerably higher. Liming costs are somewhere around £1,611.11
($2,900.00/€2,416.66) per year per litre per minute (per year per gallon
per minute). There are two cost concerns here, one being the neutralisation
of the pond water itself and the other being the loss of the Phosphoric
Acid contained in the pond water. Plant costs and savings are easily seen
here.
In this single application:
WATER SAVINGS
328,369,896 litres per year /
86,746,150 galls (US) per year
WATER COST SAVINGS
£1,154,737.20 per year / €1,732,105.00 per year /
$2,078,527.00 per year
| << back |