A cool idea for fertiliser facility

Jon Lawson

Femke Schaefer reports on how a ‘blackbox’ cooling solution is helping to enhance the growth goals of a fertiliser provider enhance the growth goals of a fertiliser provider 

Yara is a popular provider of sustainable crop nutrition solutions, supporting farmer profitability through knowledge, optimal quality and productivity. It has a leading position in nitrogen applications, and has become a total solutions provider in the market for emission control solutions. The Porsgrunn facility, about 140km southwest of Oslo in Norway, produces NPK and CN fertilisers.

NPK fertilisers are primarily composed of three main elements: nitrogen (N), phosphorus (P), and potassium (K), each essential in plant nutrition. Nitrogen helps plants grow quickly, increases the production of seed and fruit, and betters the quality of leaf and forage crops.

Nitrogen is also a component of chlorophyll, the substance that gives plants their green colour, and also aids in photosynthesis. Phosphorus, also a key player in the photosynthesis process, supports the formation of oils, sugars and starches. Additionally, phosphorus encourages the growth of roots, and promotes blooming. Potassium assists in photosynthesis, fruit quality, the building of protein, and the reduction of disease.

Yara’s current annual production capacity is: 500,000 tons of ammonia; 1,350,000 tons of nitric acid; 2,000,000 tons of NPK; and 810,000 tons (as solids) of CN.

The company started a scheme known as the Bamboo project a couple of years ago. Bamboo is a fast growing plant, which makes it the perfect synonym for the fast growth plans of Yara.

As part of this programme, the plant management has decided to increase the production capacity. One of the bottlenecks it wanted to overcome is the cooling capacity of the plant during the summer period.

As standard solutions could not achieve the required output temperature (i.e. as low as possible without having freezing problems), Bronswerk was requested to prepare three customised options to realise the preferred air conditions.

The main difference between the three options could be found in the degree of compliance with the specifications.

All of the three solutions would have the same thermal performance, however the ‘blackbox’ option, which chosen by Yara, would be the fastest and most  economical solution within the project requirements.

This option was named blackbox because the solution was the focal point, and no stone was left unturned in finding it.

Bronswerk allocated all possible resources to conduct extensive research resulting in a suitable (customised) solution. The difficulty in finding this solution lay in increasing the production performance while meeting the demands and staying in compliance with the restrictions of Yara.

The result was an air-conditioning unit different from standard solutions in terms of temperatures and allowable pressure drops.

Bronswerk was more than up to the challenges of debottlenecking and revamping existing installations to improve the capacity within the actual plot size limits while keeping the original equipment intact as much as possible.

Process optimisation

The proposed solution was especially designed to meet the critical design demands (to cool back-washed ambient air of a temperature of 13°C (100% RH) to a temperature of 2°C (100% RH). 

First, the unit needed to be able to cool down to 2°C without the risk of ice formation. Bear in mind that standard units are only able to cool down to 7°C before ice formation starts.

Secondly, the unit needed to be able to withdraw 2m3 per hour of moist from the air for the air cooling to be efficient. The natural working fluid used for this process was R717 (ammonia). To use this medium to cool down the air and to extract the moisture, an in-between circuit was designed, consisting of a compressor, heat exchangers and ducted bundles, as shown in the illustration.

There were only a few concerns. Firstly, because of applying two bundles in an existing channel the resulting pressure drop of the installation had to be compensated in some way.

For this reason Bronswerk provided the new set up with two new fans, eliminating any kind of pressure loss in the process. Furthermore, the system will be not in operation throughout the whole year. This will mainly occur during winter times when the air has less humid. For this reason a by-pass system was applied, enabling Yara to shut off the unit thereby preventing unnecessary usage.

Last but not least, droplets needed to be separated from the cooled down air. Therefore two demisters were applied on both sides of the bundles to extract the water from the air.

The project status

At the moment Bronswerk is finalising the remaining activities for this project, which will be in full operation at the end of 2016. The first major results are expected in spring 2017 but the forecasts are very positive. The research, combined with a suitable process solution, engineering and hardware supply, make this project one of a kind and underline both companies’ ambitions to be role models within the industry when it comes to process optimisation and sustainability.

For more information, visit www.engineerlive.com/process 

Femke Schaefer is with Bronswerk.

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