BY SHIREESH SWAMI
In one of the green field chemical marketing terminal located in Middle East, 29 chemical storage tanks were proposed to be installed in a very compact plot area. The client wanted to increase the terminal capacity to the extent possible in the given plot. It was neither possible to add more tanks nor to increase the diameter of the tanks due to insufficient plot area.
Out of the 29 tanks, 20 tanks were internal floating roof tanks and remaining 9 tanks were fixed roof tanks. In order to increase the storage capacity of the terminal, TCE team explored various options, deliberated on the cost effectiveness of the designs, safety aspects and proposed the following suggestions;
a) As it was not possible to increase the diameter of the tanks, it was proposed to increase the height of all the 29 tanks from 25m to 27m taking advantage of code provisions. This resulted in increase of 2 meters of operating level and the corresponding volume in each tank.
b) Instead of conventional floating roof design with carbon steel, full contact type, low height aluminium internal floating roofs were suggested for all the 20 tanks.
c) Aluminium dome roof was suggested for fixed roof as well as internal floating roof tanks resulted in lesser depth of roof structure due to reduced weight and hence more height was available for the rim seal travel in case of floating roof tanks. This allowed increased maximum liquid level of the tank and hence higher volume.
Suggestions mentioned in b) & c) above resulted in additional height of about 1.5 m available for liquid storage in each of the floating roof tanks.
Combined effect of all these three suggestions from TCE yielded net increase of about 12.5% storage volume of the terminal.
These suggestions also resulted in many intangible benefits such as;
a) Better quality as the dome roof structure, panels and floating roof panels were factory fabricated under close quality control
b) Faster installation with smaller capacity cranes and no welding and other NDTs as the connections are bolted.
c) Reduced vapour loss due to reduced emissions as aluminium dome reflects the infra-red or heat rays coming from the sun there by reducing the cost involved towards vapour recovery.
d) Enhanced safety of the terminal due to reduction in emissions and vapour cloud.
e) Expenses towards painting of the aluminium dome roofs and floating roofs are eliminated as no painting is required.
f) No major impact on the tank foundation due to increase in tank heights as the total weight of the dome roof, dome roof structure, floating roof and rim seals was reduced by almost 30%. (As density of aluminium is 1/3rd of steel density).
The raft foundation designed for tank height of 25m (on which all the tanks were anchored) was checked for the additional weight due to liquid and metal and there were no major modification needed.
All the suggestions were incorporated in the design and the terminal is due for commissioning after successful hydro-testing of the tanks. Such unique, customised value added solutions demonstrate TCE’s in-house capability of providing customised, cost effective and state of the art solutions for chemical and industrial plants.