The background
With nearly half its revenue coming from agricultural products, the voice of the farmer is an important one for Tata Chemicals. A critical finding from farmer customer surveys in India showed that farmers were unhappy with the scarcity of di-ammonium phosphate (DAP) fertiliser, one of Tata Chemicals’ products. The reason for this was that the DAP plant had low uptime, caused by a variety of factors.

 

DAP is produced by having phosphoric acid react with ammonia and crystallising the resulting slurry in a granulation process. The granulator itself is a rotary drum designed with a slope to help transport the material through the drum. Ammonium phosphate slurry is sprayed into the rolling bed of the granulator. The granulator also contains four ploughshares that enable the further ammoniation required for the final product.

 

The issue with the standard equipment was that material would build up and accumulate over the ploughshares inside the granulator. This meant that the entire production line would have to be stopped and the build-up manually broken up. Apart from the downtime of the plant, this was also a safety concern due to confined vessel entry.

 

This build-up may also lead to other process problems such as recycle duct choking, fines hopper choking, ammonia scrubber choking, reactor overflow, etc, all of which often led to several hours of plant stoppage and, consequently, loss in production.

 

What the Tata Chemicals team did was completely rethink the way the granulator worked. By changing the original design, the team solved the problem of build-up and thereby increased productivity, reduced material loss, increased output and revenues, and also improved plant safety. Remarkably, the total cost of implementing the new design was only Rs10,000. The impact — and the payoff — in terms of higher revenue, is more than Rs50 million per year.

 

The innovation
Traditionally, granulators contain four ploughshares. The Tata Chemicals team redesigned the DAP granulator to work with only three ploughshares. They also changed the position and angles of the nozzle sprays inside the drum to optimise for maximum efficiency.

The innovation was not as easy as it sounds. When the team changed the internal arrangement of ploughshares, a new problem arose: there was a slight over-agglomeration of DAP granules at the granulator outlet, leading to oversized granules being produced. The team then concentrated its attention on changing the spray distribution pattern inside the granulator.

 

Another problem that occurred was the loss of ammonia from the granulator. By the cutting down on one ploughshare, the ammonia spray zone inside the granulator bed got reduced and excess ammonia gas escaped from the granulator. This caused a decrease in ammonia scrubber efficiency. To overcome this hurdle the team analysed where the ammonia loss was occurring inside the granulator and adjusted the ammonia flow distribution to minimise the loss.

 

The payoff
This is the first time in the DAP manufacturing process that a granulator has been run with three ploughshares. The innovation hugely reduces the build-up formation over the ploughshares. As a result, plant uptime and revenues have increased, and that too, without any capital expenditure. The plant production has stabilised because frequent start-stops are now being avoided. In addition, the plant has achieved better technical efficiency of raw materials (phosphate and ammonia), which contribute nearly Rs20 million to savings. The process can be replicated in other plants, for instance, the NPK fertiliser manufacturing plant.

 

There is also a strong environmental impact as the solid particulate matter level (SPM) in the stack has gone down from 150ppm (parts per million) to less than 120ppm without any additional investment. This has a big safety impact on the surrounding community, as well as in helping to reduce the carbon footprint. But the biggest benefit is to the Indian farmer, who is assured of better supply of a vital fertiliser.