File:Demolition of a Controversial Factory - geograph.org.uk - 1125754.jpg

English: Demolition of a Controversial Factory. This is the Furnace Building on the former site of Ferro Alloys and Metals Ltd. See also 1038032.

The now skeletal building was constructed in around 1974 housing a brand new Nichols-Herreshoff furnace (or roaster) to convert Molybdenum Concentrates (molybdenum in its naturally occurring form of MoS2) to the oxide (primarily the trioxide) form.

Molybdenum's major use is as an alloying element in steels. Its primary function is to increase hardness, which it does without severely increasing the density. It also maintains this hardening effect to high temperatures, so is present in large amounts (up to 6% or more) in high-speed tool steels.

It is also present in similar amounts in high-grade Stainless Steels, particularly those used for reaction vessels and in architecture. In these alloys it has the effect of stabilising the chromium increasing the corrosion resistance.

Molybdenum sulphide cannot be used to add molybdenum to a steel because sulphur is highly deleterious. Hence the need to convert it to the oxide.

The simple equation for this reaction is:

2MoS2 + 7O2 = 2MoO3 + 4SO2

This plant replaced two hand-ravelled furnaces and included a bank of electrostatic precipitators to recover solids from the exit gases, state-of-the-art at the time.

The roaster was a cylindrical structure about 40 ft in height and 15 ft in diameter. Within it were 10 brick levels or hearths. A central rotating shaft ran vertically though the furnace attached to which were arms (two per hearth) and attached to those arms were angled "teeth". The molybdenum ore was fed via a screw onto the outer edge the top (no. 1) hearth. The teeth on this hearth were angled inward so that as the arms rotated they pushed the powder toward the centre of the furnace. This hearth (and all the odd numbered hearths) had a hole at its centre so that the ore fell onto the next hearth down (no. 2) which was bricked up to the shaft. The teeth on this hearth were angled outward, so the material passed toward four holes which lay on the outer edge, through which the powder fell on to hearth no. 3, to be gently teased inward again.

By this means the material zig-zaged down through the structure until, after between two and a half and three hours, technical grade molybdenum oxide (or roasted molybdenum concentrate) flowed from a single hole in hearth number 10. Each hearth was equipped with at least one, and up to four, gas burners by which heat could be applied into the furnace. By adjusting these burners, the speed of the feed and the shaft, and the control of where the hot gases were allowed to escape from the furnace the temperature of each hearth could be controlled for optimum production and quality.

The conversion of molybdenum sulphide to molybdenum oxide (by the above equation) is exothermic, so when in full production, the majority of the heat maintaining the temperature of the furnace came from this reaction, rather than the gas burners.

The furnace occupied the right-hand side of the building as seen from here, so that side had a series of mezzanine floors giving access to all levels of the furnace. At the very top there was a full floor level with the top of the furnace where the feeding equipment was located. The level of this floor can still be made out as the balcony on the right was accessed directly from it. Originally a walkway ran along the length of the roof from the access ladders which can still be seen. For a few years in the early 1990s a weather station was mounted there, so I used to climb up a couple of times a week to check on that. The left-hand side of the building was open from ground to roof level and contained product storage hoppers and a blending plant installed in 1981.

The furnace ran continuously with shut-downs at Christmas ( 1 - 2 weeks) and the Wakes Weeks (2 - 3 weeks). The Glossop Wakes Weeks were traditionally the last two weeks in July, which was rather inconvenient as most years only the second of these fell within the school holiday.

The furnace was operated by two men; the charge-hand was responsible for keeping the furnace in good order, this mainly consisted of observing the flow of the material though the plant by means of four inspection doors on each hearth level and manually clearing blockages using long-handled rakes and pokers, he was authorised to make small adjustments to the furnace operating parameters (Burner levels, outlet damper settings, shaft speed and such); the second-hand mainly ensured that the feed was supplied with ore and the outlet hoppers were filling correctly.

To cover the entire week a shift system consisting of four teams was operated. Shift times were 06:00 to 14:00, 14:00 to 22:00; 22:00 to 06:00 Each team worked six days on; two days off starting back on the next shift. This resulted in a 24 week cycle.

The new roaster was capable of processing much more molybdenum than the previous plant and as a result produce much more sulphur dioxide than the small (approx 120 ft) brick chimney which serviced it could possibly disperse and the company applied for planning permission to erect a 400 ft steel chimney - this was the calculated minimum height to allow for the acidic gases to disperse from the narrow confines of Glossopdale. There was some debate and in 1977 the company was allowed to erect a 300 ft chimney on an unusual 10 year temporary planning permission - on the understanding that the company would undertake within that decade to ensure the reduction of the SO2 emissions (a clause completely outside the council's jurisdiction to enforce).

By the end of 1978 the erection of the "Glossop Chimney" seen here to the right, was complete.

When the furnace ceased production in September 1995 (after many wranglings, which I will chronicle elsewhere) it was the last remaining molybdenum roaster in the United Kingdom. While the site continued to be used to process molybdenum for a further ten years, from then-on the incoming material was molybdenum oxide.

After the furnace ceased production it remained in place for a while and was finally broken-up for scrap in 1997. For a while the building was used for storage (ground floor only) until an oxide briquetting plant was relocated into it in 1998. Briquette production ceased in 2000 and the building was again used mainly only for storage.