Thermal Detection helps fertiliser manufacturer

The Company is the UK's premier fertiliser manufacturer and is a major supplier to the process chemicals industry.

The primary products produced at the Billingham site include ammonia, nitric acid and ammonium nitrate. Part of the production process involves the control and monitoring of product in a catalyst vessel. As part of an upgrading project, GrowHow required to implement an improved method of determining both the catalyst temperature and its level within the NH3 IV Methanator D303 vessel.

Having had previous contact with Thermal Detection Limited in other applications in the field of temperature measurement, a request was made to us to design a suitable unit to satisfy GrowHow’s requirements. The catalyst vessel was located in a designated hazardous area and to meet the requirements of the project, several points of measurement would be needed. 

This was to be able to correctly identify the catalyst temperature caused by the exothermic reaction and to provide an inferred indication of the product level. For simplicity it was decided that a thermocouple based arrangement would be the preferable route to take.

The final design involved a cluster of six 3.0mm diameter type ‘K’ thermocouples each contained within a 6.0mm diameter guide tube and held within 35mm diameter support rings. Each guide tube terminated at a different length between 1.5 and 5.5 metres.

The ends of the guide tubes were angled such that the thermocouples inside could make direct contact with the inner wall of the stilling tube when the assembly was finally installed.

The thermocouple terminations were housed in a top mounted enclosure and wired back to the control room via an appropriate safety barrier.

Retrofitting units in this manner is often fraught with unpredictable problems, not to mention the transportation of them to site in the first place, particularly when they involve relatively delicate items several metres in length. However, they arrived at site in the condition in which they left our workshop and GrowHow found that the unit was able to be slotted in to the 38.1mm bore of the stilling well without encountering any problems.

GrowHow UK Limited operate from two manufacturing bases, one based in Billingham, Cleveland and the second, together with the head office at Ince in Cheshire.  The Company is the UK's premier fertiliser manufacturer and is a major supplier to the process chemicals industry.

The primary products produced at the Billingham site include ammonia, nitric acid and ammonium nitrate. Part of this production process involves the control and monitoring of product in a catalyst vessel. As part of an upgrading project, GrowHow required to implement an improved method of determining the catalyst temperature within the NH3 IV Methanator D303 vessel.

Having had previous contact with Thermal Detection Limited in other applications in the field of temperature measurement, a request was made to us to design a suitable unit to satisfy these requirements. The catalyst vessel was approximately 7 metres high, 4 metres in diameter and located in a designated hazardous area.

To achieve the desired data it was decided that several points of measurement would be needed. This was to be able to correctly identify the catalyst temperature caused by the products exothermic reaction. For simplicity it was decided that a thermocouple based arrangement would be the preferable route to take.

Since the catalyst vessel was part of the original Billingham ICI Heavy Chemicals complex, it was several years old and the specifications relating to it were few. What was known was that the entry point for the thermocouple assembly was via an entry on the top of the vessel.

However the entry itself was part of a dip pipe with a closed bottom and only having a 38.1mm internal diameter and welded to a 2” ANSI 300 RF flange.

It was realised that in order to ensure a satisfactory response time, a method of ensuring that the thermocouples were in a position to achieve this was a critical part of the exercise.

Several designs were investigated, but the final design involved a cluster of six 3.0mm diameter type ‘K’ thermocouples of varying lengths. Each of the thermocouples were contained within a 6.0mm diameter guide tube and held firm within six 35mm diameter support rings. The centre of the support ring had a 6mm diameter round bar running the entire length of the assembly to provide rigidity. It also extended by a length of 5mm more than the lowest thermocouple to indicate that the bottom of the dip pipe had been reached when being installed.

Each of the guide tubes terminated at a different length between 1.5 and 5.5 metres. The ends of the guide tubes were angled to allow the thermocouples to make direct contact with the inner wall of the dip pipe when the assembly was finally installed.

The six thermocouples passed through a multi-hole, stainless steel sealing gland with a Teflon® sealant. The sealing gland was fitted on one side to a machined stainless steel insert that would slot into the top of the dip pipe. 

The upper section was connected to a stainless steel enclosure housing the thermocouple terminations. These were then wired back to the control room via an appropriate safety barrier.

Retrofitting units in this manner is often fraught with unpredictable problems, not to mention the transportation of them to site in the first place, particularly when they involve relatively delicate items several metres in length. However, they were shipped the short distance to site in a specially prepared wooden case and arrived intact.

GrowHow found that the unit was able to be slotted in to the 38.1mm bore of the dip pipe without encountering any problems. Once fitted and with the flange bolted down, the thermocouples were individually pushed down for the final 15mm so that the thermocouple tips were hard up against the internal wall of the dip pipe. The sealing gland was then finally tightened to maintain their position.

This system has now been in operation for over a year and the data collected has found to be very effective in monitoring the exothermic reaction within the desired timescale.

Consideration is now being given to carrying out a similar installation on another vessel, but this time involving 10 thermocouples with an overall length approaching almost 7 metres.

© Thermal Detection Limited / BulkInside