Colonial Coal Mining
The story of the Rotowaro Carbonisation Works is integrally linked to that of coal mining as an allied operation designed to reduce waste and increase profitability without increasing the onus on workers. Many of the workers came from jobs in the adjacent coalfield and lived at Rotowaro Township, the lives of both workforces and their families were integrally entwined. For this reason the growth and changes to colonial coal mining are outlined here to set the scene for detail of such a coal slack processing plant.
Early coal mining activity was largely focused on the South Island's West Coast and as with elsewhere in the world, the nature of the industry meant that the miners lived in coal towns established around the mining activity or in satellite camps. The miners of colonial New Zealand largely lived in their own world in environments that were both harsh and inaccessible, unlikely to have been developed, but for the coal seams. The degree of isolation and remoteness was not as marked with the development of the Waikato and Otago/Southland coalfields. As transport improved so miners were able to move on to more diverse towns such as Greymouth and Huntly. As migrants, these transplanted British colliers also suffered isolation, driven by fear from the colonial coal masters of the late 1870s of 'the twin evils of Methodism and unionism'. Confirmation of this status saw the miners labelled as outsiders who lacked the 'pride of colonials' described at the time as having, 'lower ideas of life', 'inferior morals and stronger prejudices' than the general population. They became isolated by nationality as well as occupation, even in the 1940s when coal towns were noted for a discordant 'foreign twang'. Although the coalfields had a male dominated work force, many miners brought families to New Zealand with them and their wives were often from mining families and had worked above ground in British coalmines.
Early mining in New Zealand was owned and operated by private operators with shipping companies monopolising this through absentee owners. Over time, government support, encouraged by the colliers, was viewed by owners as interference. Government involvement gradually moved to actual investment in mining companies and ultimately to nationalisation of the industry. For the miners, despite many failed attempts, it was not until 1923 that a national body, the United Mine Works formation was established as a coherent response to wage cuts in1922-3. For miners in bigger towns such as Huntly establishment of a local borough council in the first decade or the twentieth century became an opportunity for union influence, as did school committees.
Early living conditions in the towns and camps supporting coal mines, were insanitary and few homes reached a standard of comfort in city homes of blue collar workers. Government looked to the coal towns of the Waikato fields to change this situation. There were shortages and rents were believed to be too high, but at Rotowaro and Pukemiro it was seen as possible for these to be made into 'extremely attractive garden villages' and for Huntly having the potential to becoming a 'model suburb'.
The rapid growth of the dairy industry and associated factory demands along with the expansion of domestic and industrial markets in the booming Auckland area, were the major factors for the amalgamation and expansion of the existing pits in the Waikato, by the Taupiri Coal Company. Begun in 1876, coal production in the Waikato increased by 400 per cent by 1914 and its share of the national product had risen from 7 to 15 per cent. This trend gathered momentum and by 1935 Waikato had eclipsed the West Coast as the leading coal centre at the expense of Otago Southland. Mostly migrants, nearly 2,000 newcomers made this growth possible.
Turning Waste to Profit: Coal Waste Processing Plants
Prior to the construction of the Rotowaro Carbonisation Plant, briquette producing plants were constructed at some collieries to utilize the slack coal that otherwise had to be dumped as waste. The disposal of slack coal had already been recognised as a matter of national importance as early as 1891. Around that time, construction of a briquette plant seems to have started at the site of the Brunner mine. However, this project was abandoned before it was finished. In 1892 a briquette manufacturing plant that belonged to the Grey Valley Coal Company was operating in Christchurch. According to a contemporary newspaper account this was the only machinery of its kind in the Southern Hemisphere at the time. The plant was situated in the south-east corner of the city. It produced six ton of briquettes per day with demand outstripping supply. In 1906 a briquetting plant was constructed at the Seddonville State Mine. In 1909 a briquette plant was operational near Westport processing slack from the nearby Stockton coal mine. This may refer to the same plant since the newspaper article mentions the arrival of an expert to introduce a new process in coal briquetting. In December 1912 this facility was dismantled after the lease of the site expired.
The most significant works established in New Zealand to turn slack coal in to profitable product was established at Rotowaro Coalfield.
The Inception of the Carbonisation Works
The rapid growth and success of the Waikato Coalfield, provided the company with the not only the ability but also the necessity to invest in establishing a coal slack processing plant. The Rotowaro Carbonisation Works was established to dispose of the huge amount of waste coal (slack) that was generated at the Rotowaro Mine that had been operated by the Taupiri Coal Mining Company since 1917. Because of its size the slack was commercially unviable to sell and large quantities had to be dumped to meet demand for the screened grade of coal.
It not only required the availability of extensive dump areas, but also presented a significant fire hazard and was an enormous waste of a potential energy source. The coal commonly mined in the Waikato tends to disintegrate on exposure to weather. Thus nearly 45 percent of all coal mined ended up as slack waste after having passed through a three-quarter inch (1.905 centimetre) square mesh screen. As a result, in the Waikato alone, around 150,000 tons of slack coal was produced annually. Even though the Auckland Power Boards' steam generating station at Kings Wharf used about 80,000 tons of that, it still left the region with a significant amount of coal waste to deal with.
Investigations into other uses for the slack were also instigated by the anticipated effect the governments hydroelectric power scheme would have on the market for slack coal. It was widely known that the Kings Wharf steam generating station would be closed once the Arapuni Hydroelectric station was brought online. This would result in the loss of a major client for the Waikato coal mine owners. Therefore they began to investigate English and continental systems of coal processing that would turn slack into a commercially viable product.
At an early stage coal carbonisation was considered to be an option and by 1923 various carbonisation processes were investigated.
Subsequently, in 1924 a small experimental carbonette press was acquired and experiments using New Zealand coal were carried out. It soon became clear that New Zealand coal was not suitable for producing carbonettes without a binding agent. Other issues identified were suitable heaters for the moulds, the size of the coal, the nature and amount of binders required and the pressure required for moulding carbonettes.
In 1925 Waikato coal was sent to England, Belgium and Germany for trialling in a number of processes so as to obtain a report on its suitability for carbonisation. The German trials turned out to be the most favourable. Earlier research of coal processing technologies carried out by the government had already indicated that the coal mined at the Waikato mines had characteristics similar to German coal.
Choosing a Carbonisation Technology and Purchasing a Plant
As a result of these series of experiments and trials the German Lurgi process was chosen. This process was owned by the Metallgesellschaft AG based in Frankfurt, Germany. The Lurgi process was the most common carbonisation process in use at the time for processing lignite, the lowest grade of coal and the type mined in the Waikato at the time. It is brownish-black and has a high inherent moisture content. The process was in use in Canada, the USA, Greece, Hungary and Germany.
The Lurgi process uses externally heated steel retorts for low-temperature (max. 650° Celsius) carbonisation to improve the quality of the fuel, creating virtually smokeless carbonettes. This was achieved in three steps.
1. Coal slack was carbonised at a low temperature to leave between 7 and 10 percent of volatile matter, thus creating a semi-coke.
2. As by-products tar, oil and pitch were produced.
3. Carbonettes were created from the semi-coke using the pitch created as a by-product as part of the binder required.
The aim was to produce a high-grade, smokeless fuel that would be useable for railway and domestic purposes and also for power plants. It was foreseen that 40,000 tons of high grade carbonettes, 2000 tons of diesel oil, 320 tons of fuel oil and 2900 tons of pitch could be produced per year. In 1929 the Waikato Carbonisation Ltd was set up as a subsidiary of four local coal companies. It was responsible for the processing of the coal slack and returning the revenue back to the coal companies.
A slack processing plant was acquired from the Lurgi Metallgesellschaft to be erected near the Rotowaro mine. There it could handle all slack coal produced at the Taupiri Company mines efficiently. If necessary, additional slack would be available from the nearby Pukemiro and Renown mines. Before making the final decision regarding the purchase of the plant the mining companies were promised that the Railway Department would purchase substantial amounts of carbonettes once the plant was running. This undoubtedly had an influence on the decision to buy the plant.
The Construction of the Plant
In November 1929 D.G. Whitwell arrived in New Zealand to make preparations for the construction of the plant. He was the main engineer in charge and represented Fuel Industries Ltd who owned the British rights to the Lurgi Process. In the same year W.G. Heptinstall, a Canadian engineer, was appointed manager of the Rotowaro Carbonisation Works. He was a very experienced engineer, having been in charge of the Lurgi Carbonisation Plant in Saskatchewan, Canada.
The main parts of the plant were shipped from Europe in February 1930. August Finkenbeiner, a representative of the Metallgesellschaft accompanied the plant to supervise its construction. He was later joined by a second engineer, Mr Müller, who not only assisted in the supervision of the plant but was a carbonisation expert also.
The plant arrived on 22 April 1930 on the Ruahine. Since the New Zealand government recognised the importance of the plant and the need for its technology, most was landed duty free. One hundred railway wagons were needed to transport the plant from Auckland to Rotowaro. In addition to the material purchased from the Lurgi Metallgesellschaft, several parts needed to be constructed in New Zealand. These included the hoppers for the Retort Building, the steam boilers, the various bunkers, the bricks and the conveyors.
It took almost a year and 60 New Zealand staff to erect the plant. In May 1931 the plant started operating on an experimental basis. On 10 June 1931 the plant was officially opened by the Hon. W.A. Veitch, the Minister of Railways and the Hon. A.J. Murdoch, Minister of Mines. The opening was attended by around two hundred guests, many having travelled from Auckland on a train powered by carbonettes produced at the carbonisation works. Among the guests were members of parliament, leading business and industrial figures and local government representatives. At its opening the plant was hailed as a major technological advance and it was stated that it would be the first of many plants that would serve the coal mining centres. However, it would remain the only low temperature carbonisation plant in New Zealand. It was not until 1958 that another low temperature carbonisation plant was built in the Southern Hemisphere. Research has shown that although some Low Temperature Carbonisation plants using the Lurgi technology are still operational elsewhere in the world these are all of a much later date. All plants contemporary to the Rotowaro Carbonisation Plant have been closed and subsequently demolished.
The Initial Years of Carbonette Production
Predictions about the level of demand for carbonettes were not initially realised. The main factor that impacted on the reduced demand, production and operational ability of the plant was the Great Depression and ironically, at a time when creation of employment was so crucial, this lack of demand meant that the plant was only able to operate for six months of the year through to 1934. However, the mining operation was also reduced during that period, to two or three days a week, thus significantly reducing the amount of slack coal produced. This situation did not help the struggling Carbonisation Works, which made barely enough money to pay for its operating expenses. Despite these difficult circumstances a second carbonette bunker was erected in 1933 to increase cooling capacity.
In 1934 the Railway Department failed to renew its contract after tests had shown that the carbonettes were not suitable for its locomotives. It seems however, that this decision was, at least to some extent, governed by the relatively high cost of the carbonettes compared to the normal sized coal the Waikato mines produced.
The government took notice of the situation the Carbonisation Works was in. It also realised that large amounts of slack were still being wasted and in 1935 the Hon. P.C. Webb, Minister of Mines, stated in his annual report that: 'the unnecessary wastage of coal has always given me the greatest concern'. Subsequently, in an attempt to increase demand the government started an intensive advertising campaign for carbonettes in 1935. At the same time, in an effort to try and to minimize the amount of coal wasted, screens with a smaller mesh were installed at the Carbonisation Works to increase the amount of slack coal being processed. The advertising campaign resulted in the demand for carbonettes increasing to 17,000 tons in 1936 and 21,000 tons in 1937. From 1937 the demand outstripped the supply of slack coal and thus solved that problem for the Waikato mines. From 1936, carbonettes were sold at Woolworths in cardboard boxes. Initially, carbonettes were also shipped to Nelson, Dunedin and Bluff, but this practice was discontinued when demand in the North Island could not be met.
In 1936 a gas engine generator was installed to generate part of the electricity demand of the factory.
From 1936 the plant operated for 10 months a year. The remaining two months a year were necessary for staff holidays and maintenance. When both retorts were operating it took 60 men to keep the plant running. The men worked in a shift system, since it was necessary to keep the plant going for 24 hours a day, seven days a week because starting and shutting down the plant each took between 10 and 14 days. The average employee worked 42 hours a week, receiving higher rates for Saturday and Sunday shifts.
During the initial period the markets for the by-products were very slow. Light oil was distilled in the tar distillation plant and used as a weed killer and fuel oil. Initially, the tar produced yielded about 30 per cent of the pitch required for the carbonisation process. The additional pitch needed for the production of carbonettes was imported from Trinidad. In 1938 the original tar distillation equipment, which by then had become seriously corroded, was replaced with a Wilton continuous pipe still. This increased the tar production to about 70 per cent of pitch required for the production of the carbonettes. That same year the company was awarded a contract to provide creosote for the timber treating plant built by the Forestry Department near Rotorua. This turned the production of the heavy distillates into a profitable business. Additionally, during the war substantial quantities of creosote were exported to India and large quantities were used in New Zealand for the preservation of sand bags used for defence purposes.
During World War Two petrol shortages led to the manufacturing of gas producers to power private cars and trucks. To meet the demand for fuel for these, the company marketed its char under the name 'Waicarbo' which was subsequently sold all over New Zealand. At its peak production reached 1000 tons a month.
Production Post War
With the end of World War Two the demand for 'Waicarbo' stopped, and was replaced with a similar, but larger, fuel developed and sold under the name 'Raycarbo'. This was mainly used for 'Esse' stoves and heaters. Although the demand for Raycarbo never increased above circa 800 tons a year, by this time the carbonettes had become very popular as a household fuel and for commercial use in bakers ovens and sales remained steady between 1946 and 1960.
By the mid 1950's the plant produced a range of products: carbonettes, screened carbonised coal, creosote, pitch and gas. By 1956 the government owned two thirds of the company, the other third was owned by Pukemiro Collieries. A drop in sales in 1962 was countered with another extensive advertising campaign and sales returned to levels previously achieved.
In 1964 the economic life of the 1930's retorts came to an end and investigations were undertaken looking into replacing the plant. Lurgi came up with an offer of a new plant with three new retorts including a treatment facility for phenol solvents with a cost estimate of around 20 million German marks. The price was probably deemed too high since this offer was never followed up. In 1968 the plant became solely government owned under the State Coal Mines Department. By 1974 the demand for carbonettes had fallen again but this was offset by demand for char by New Zealand Steel Ltd for its steel production process.
The First Explosion in the Plant
On 7 March 1974 an explosion occurred at the distillation building. The explosion was described as looking 'like a volcano erupting from Huntley, nine miles away'. Another witness, reportedly working nearly half a mile (800 metres) away felt a blast of hot air on his back. When he looked around he saw a fireball rising to 400 feet (120 meters) in the air. The explosion seriously wounded one man, who died later in hospital, and set several nearby buildings on fire. The still building was gutted and the main retort building was severely damaged. Although repairs were undertaken immediately the production of carbonettes, creosote and pitch had to be stopped, the production of char for New Zealand Steel continued though.
Upgrading the Plant
In 1976 Lurgi Metallgesellschaft was again asked for a quote for replacing the retorts, but no action was undertaken. The following year plans were prepared to replace the entire plant with a modern Australian char plant of similar capacity as by now char was the most important product manufactured at the plant. This idea was abandoned in favour of a partial upgrade of the complex. Work carried out included the reconstruction of one of the retorts, the installation of new tar recovery machinery and new carbonisation machinery. This was carried out in between 1979 and 1981 for a total cost of 1.4 million dollars.
In 1981 a wood charcoal barbecue briquette production facility was built near the No 2 carbonette bunker and screening plant. However, this did not prove to be an economic success. In 1986 the production of carbonettes stopped permanently. The plant continued to produce Raycarbo fuel for the domestic market, char for New Zealand Steel and creosote for Railways for the treatment of railway sleepers.
In 1985 the building known as the Rotowaro Carbonisation Works Adit (also known as the Mine ventilation Fan Structure) was registered as a class C building (Record no. 4282). At the same time the Store Shed (or Loco Shed) was registered as a class C building (Record no. 4283). In 2001 both were changed to Historic Place Category II registrations. These buildings were not a part of the Carbonisation Works, but of the Rotowaro Industrial Precinct located to the northeast. These buildings were both related to the actual mining activities carried out at the nearby underground Rotowaro Mine.
The Second Explosion in the Plant and its Subsequent Closure
In 1987 another explosion occurred at the plant, this time at the retort building, followed by a major fire. Operation of the plant ceased while options were being considered. Although the company was insured adequately for the repairs to be carried out, new safety regulations meant extensive changes were necessary for production to resume. The decreased demand for Raycarbo and char made new investments economically unviable and subsequently it was announced on 24 July 1987 that the plant would cease operations permanently on 7 August 1987. At the time of closure it employed 25 workers and management staff. Following closure the company went into liquidation. This left the workers without any redundancy payments and it took until September 1994 before the government finally decided on a $1500 ex gratia payment to those workers.
The workers' attitude towards the Carbonisation Works has always been ambiguous and changed over time with the changing attitudes towards health and safety issues. In the early days the emissions from the works, although smelly and dusty, were supposedly healthy and it was said that anybody suffering from the whooping cough just had to be sent to the plant and that would cure them. Others called it 'the filthiest place that was ever made' and complained about the black, greasy sort of dust it emitted which was almost impossible to clean off. However, the carbonettes it produced were a great success, especially with the workers getting them for nothing or at a very low price. With regards to the safety issues one interviewee casually remarks that starting the plant was 'rather a dicky business'. The general public's view of the place has also been one of extremes over the years. For some it is 'Waikato's number one environmental problem' that should be completely cleaned up. Others have documented the works for exhibition purposes or as part of an art and design course.
The Rotowaro Carbonisation Works as a whole was registered in 1991 (Record no: 7013). Subsequently, in 1992, two buildings within this historic area, the Main Structure (the Retort Building) and the No 2 Screening Structure and Bunker were registered as Category I Historic Places (Record nos. 4171 and 4172 respectively).
Since its closure the Rotowaro Carbonisation Works has been targeted by looters and thieves. Metal as well as wooden parts have been removed from the various buildings. The main building targeted has been the No 2 Screening Structure and Bunker. This building, mainly constructed out of wood, has had large timber sections removed over the years. Other buildings have had metal parts such as its cladding and machine parts removed, probably to be sold as scrap metal. After the creation of the bund (see below) the looting has diminished somewhat, as the ponded water makes it harder to get to the structures. However, even though the looting has affected some buildings more than others it has not compromised the overall integrity of the plant or destroyed essential elements that communicate how the plant operated.
Cleaning up the Site
Soon after the company went into liquidation appeals were made to clean up the site. It was recognised that over the years it had been allowed to spread it contamination beyond its 10 ha site without constraint because the plant started operating long before the Town and Country Planning Act of 1958 and the Water and Soil Act of 1967 and so was not subject to any controlling authority. It meant that the Carbonisation Works could, after the introduction of both these laws, quite legally get by on its existing use right and keep discharging any waste of cooling water into the Awaroa Stream. Even after 1976, after a water right was issued to allow for these practices, little attempt was made to clean up the discharge before it entered the stream. Even when a fine was issued, this did not improve the situation because 'it wasn't a particularly big fine'. When in 1981 the water right expired and was not renewed, the company did stop discharging into the stream and started a waste incarceration programme. Its capacity proved inadequate and the company began storing the waste on site thereby creating three ponds that eventually overlapped to create one big pond measuring about 2000 m2. The company tried to use micro organisms to reduce the toxicity of the ponds, but that failed because of the sheer volume of toxic waste produced.
After the company went into liquidation some work was done to minimise the risk posed by the ponds. These consisted mainly of shoring up the sides of the ponds and roofing them over to prevent rainwater getting in and causing overflow. However, over the years the banks started showing signs of seepage and collapse and by late 1990, shortly after the elections brought in a National government, it was decided that action had to be taken. The previous Labour government had rejected the idea of a clean-up following advice from the Treasury department saying that the government was not legally responsible for the site. During the election run-up, the local National candidate had promised that 'Waikato's number one environment problem' would be cleaned up. Initially the National party seemed to back out of their promise, but it decided in December 1990 to ignore Treasury's advice and agreed to fully fund a cleanup operation.
Waikato Regional Council (now Environment Waikato) drew up a plan for the cleanup and managed the actual work on behalf of the Crown. This cleanup started in early 1991. Liquid from the ponds was pumped into trucks and carried off to the Kinleith Pulp and Paper Mill in Te Kuiti, where it was incinerated. In total about 11,000 cubic metres of stored liquid was removed. The empty ponds were subsequently filled with the remaining liquids, totalling about 4000 cubic metres. This sludge was treated by means of bioremediation, the first time this was carried out in New Zealand. Extra nutrients and air were added to the mixture to stimulate bacteria to break down the contaminants. By August 1995 this resulted in about 500 cubic metres of relatively dry, inert material. This was mixed with clay, locally spread over land, covered with clay and contoured to direct any runoff away from the Awaroa Stream.
Expansion of the Nearby Opencast Mine and Creation of the Bund
From 1992 onwards Coal Corp expanded the opencast mine to the east and south-east of the carbonisation works. As a result of the expansion the nearby Rotowaro Industrial Precinct was completely destroyed. This was the location where the two category II buildings were located. The expansion covered part of the registered Rotowaro Carbonisation Historic Area, destroying several buildings, including the fitters workshop and the new storeroom. It also destroyed the footprint of a number of buildings that had already been demolished by then, such as the old staff lunchroom, the electric shop, the old administration office, the weigh bridge and the old laboratory. The overburden that was removed to get to the underlying coal was used to create a bund around the site. The bund was created by digging a key into the underlying stable clay deposits and filling this in with the overburden material. The purpose of the bund was to prevent contaminated water running into the Awaroa Stream. As a result the bunded area flooded with water up to 2 metres deep, thereby effectively prohibiting access to the buildings.
This was an undesirable environment for the steel buildings to be subjected to, especially since the water table fluctuated throughout the year. Therefore, it was decided in 1995 to insert a drain in the bund for water to be released into the adjacent Awaroa Stream. However, the drain was not opened until late 1998 or early 1999. Water testing was carried out and the water was not deemed to be an environmental problem. This alleviated the water problem somewhat although during wet periods the site is still partially inundated.
Since 2003 new steps have been undertaken to identify methods to remove the remaining contaminants from the site and to identify means to stabilise the heritage structures and elements of the plant. The goals of this remediation were to ensure that the site does not have a significant adverse effect on the Awaroa Stream, to ensure that the site should no longer pose an unacceptable risk to the public and to reduce the rate of deterioration of the structural elements by identifying methods of stabilisation. For that purpose a study was undertaken in 2007 funded by the Ministry for the Environment, the NZHPT and Solid Energy New Zealand. As a result, a remediation action plan is currently being produced that will be undertaken during the summer of 2008-09.
The Rotowaro Carbonisation Works was the first plant of its kind in New Zealand and despite intentions otherwise, it remained the only one that was built. The Lurgi low temperature coal carbonisation process was in use in several countries worldwide in the period between 1920 and 1950. In some countries it is still being used today, albeit with variable success.
Although the process originates from Germany only one example of a carbonisation plant using the Lurgi process has been found. In 1935 a brown-coal processing plant was built in Espenhain, near Leipzig. The main purpose of the plant was to generate power for Germany's heavy industries. To maximise the amount of coal used the plant applied the Lurgi-spulgas technique to manufacture carbonettes from the slack coal. These would then be used as a fuel in power plants generating electricity and steam. After World War Two the plant came under Soviet control and even became a Soviet company until 1954. The plant produced large amount of tar, cokes and oil products for over 50 years. In the 1980's environmental awareness led to large public protests because of the pollution caused by the outdated equipment. Just prior to the German Reunification the socialist German Democratic Republic decided in February 1990 that all carbo-chemical systems in the Republic should be closed. On 27 August 1990 the plant at Espenhain was closed down. It was replaced in 2004 by a solar power plant; the biggest in Europe at the time of its construction. At the start of World War Two twelve brown-coal processing plants were operational in Germany. These used the low temperature carbonisation process to make synthetic fuel, in order to make Germany independent from foreign supply for its war efforts. However, these did not manufacture carbonettes for the domestic market and no longer exist.
The United Kingdom
No references have been found to carbonisation plants using the Lurgi technique in the United Kingdom. At the time the Rotowaro Carbonisation plant was first considered research showed that carbonisation technologies used in the UK were not suitable for coal found in the Waikato. This suggests that the Lurgi technique is not suitable for coal deposits commonly found in the UK. In the beginning of the twentieth century several coal carbonisation plants were constructed. However, most of these did not produce carbonettes for the domestic market, but rather gasified coal to supply power houses and towns with gas. The Phurnacite plant in Abercwmboi, Wales, operated in a way similar as the Rotowaro Carbonisation Works. The Phurnacite plant was opened in 1939, in an area that had been mining coal successfully since 1851. Like at Rotowaro, waste coal was crushed, dried and mixed with pitch to produce carbonettes. The Phurnacite plant produced approximately 1 millions tons of carbonettes per year during its peak. By the mid 1970's demand dwindled for carbonettes and awareness of its environmental impact caused the plant to be closed in 1991, after an attempt to upgrade the plant had failed. Since it was closed the plant has been destroyed.
In 1929 in the Gelliondale Briquette Plant was constructed in Victoria. The plant did not carbonise coal slack; instead it produced briquettes by binding raw coal slack with pitch. This plant produced briquettes between 1934 and 1944. In 1950 the plant was closed down. Today only some of the footings remain. In October 1956 a Lurgi Gasification Plant was opened at Morwell, Victoria. The Lurgi process was selected because the by-products were expected to improve the economic returns of the plant. However, this plant did not produce carbonettes for the domestic market, rather producing 15,000,000 cubic feet (424752.7 cubic metres) of gas per day to supply Melbourne with town gas. The plant ran until 1970 when it became economically unviable due to the advent of natural gas.
In 1920 a carboniser with auxiliary buildings was constructed by the Canadian Lignite Utilization Board near Bienfait, Saskatchewan, Canada, between two major collieries, the Western Dominion Colleries and the Manitoba and Saskatchewan Coal Company of Winnipeg. This plant became operational in 1921 but none of the carbonizing processes used were successful, forcing closure in 1923. In 1929 a Lurgi plant was erected in Black Diamond (Alberta, Canada) under supervision of German engineers. The plant went into production in 1930 and although good quality briquettes were produced they would burn from spontaneous combustion during storage. Since this problem could not be solved the plant was shut down. The plant was bought by John H. Macdonald of Winnipeg who, with help from three hands from a Lurgi plant in Dickinson (North Dakota, USA), managed to run it successfully until 1963. Subsequently the plant was sold on again and it successfully produced char until 1982, when it was shut down permanently. The only Lurgi plant located in the USA known to have produced carbonettes is the one in Dickinson. No further information has been obtained about this plant. In 1984 a coal gasification plant started operating near Beulah, North Dakota. This plant uses the Lurgi technique to produce natural gas. It also produces many by-products and is running profitably. Currently this is the only commercial coal gasification plant operation in North America.
At least two carbonisation plants have been built on the Indian subcontinent, one in Neyveli and one in Dankuni. The one in Neyveli was part of a larger complex of power stations and coal processing plants located on one of the largest Lignite coal reserves of India. The briquetting and carbonisation plant was built in 1966 using equipment supplied by a consortium of West German firms. As with the other low-temperature carbonisation plants the by-products were an important argument to build the plant. This plant stopped operating in 2001. The Low Temperature Carbonization (LTC) plant in Dankuni was commissioned in 1990 but has been incurring losses since it started operating. Coal India has been trying to sell this plant for a number of years now but so far no serious buyer has been found.
The Rotowaro Carbonisation Works is located in the heart of the Waikato coal belt approximately 8 km south-west of Huntly. The facility is located alongside the Awaroa Stream, a tributary that feeds into Lake Waahi. To the south and southeast of the plant, pit Awaroa 4 of the Rotowaro open cast mine is located. This is one of several large opencast mining pits that either have been or are still being exploited by Solid Energy NZ Ltd. The Rotowaro Coalfield is surrounded by farms and large tracts of Pinus radiata (Radiata pine). Historically the site sloped gently towards the Awaroa Stream. However, since mining began in this area overburden deposits have altered the physical landscape dramatically. The overburden has been used to fill low-lying swampy areas, to create bunds of various sizes to prevent surface water runoff into the Awaroa Stream and to create ponds for the treatment of waste water using biological means. As a result, the natural drainage flows have been severely disturbed and has created a situation where the area of the remaining buildings is flooded most of the year.
The geology of the site is as follows: on top of the old surface there is a layer of fill materials of variable thickness. This was deposited during the 1992 clean-up and constitutes the overburden from the nearby Awaroa 4 pit when it was prepared for coal mining. The most prominent feature is the bund created between the Carbonisation Works and the Awaroa Stream. This bund is about 10 metres high. The Carbonisation Works is built on a layer of Taupo volcanic ash. This layer is between 1.5 - 3 metres thick. This ash layer is situated on top of a fire clay layer of variable thickness. The layer of fire clay covers the underlying coal deposits, the Waikato Coal Measures.
Currently the site is not managed. This has led to a wild cover of vegetation, mainly gorse, flax and pampas grass. The bund still impounds rain water on the site, immersing the foundations of at least part of the buildings. The water table fluctuates throughout the year, creating very unfavourable preservation conditions for the buildings. As described previously, the site is under constant threat of theft looting and vandalism.
The 26 buildings/structures are ordered and described in the sequence in which they are used in the carbonette production process from conveyor belt through to final product. (See Appendix 6.2 of the registration report for a plan of the lay-out of the site and the location of each individual structure.)
Built in 1930-1, original feature of the complex.
This conveyor was one of two that fed the slack coal from the screening plants at an adjacent colliery to the coal bunker for storage.
A steel framed structure with corrugated iron cladding.
Built in 1930-1, original feature of the complex.
Storage facility for slack coal with a capacity of holding 1000 tons. Slack coal was transported to the bunker by means of an enclosed belt conveyor approximatley 300 metre in length. The slack was transported to the adjacent retort house through an automated plough device dragged to and fro by means of a chain along the length of the bunker outlet near the base. This plough trickled a mix of coarse and fine coal slack onto a belt that conveyed it to the bucket elevator which is part of the Lurgi Retort Building.
Free standing steel framed building with a corrugated iron roof; the lower half is clad with steel panels. This building is largely intact and in good condition.
Magnet House aka The Electric Sub-station
Built in 1930-1, original feature of the complex.
Since the building is no longer extant no description is available for this structure. It does however show on photos taken around the time of the construction of the plant. This building housed an electromagnetic machine which removed any pieces of iron or steel which may have found their way into the slack.
Historic photos show it was a small, probably square, building with a gable roof. All that remains are remnants of the foundations. From photos taken in 2007 it seems to be have been constructed from steel and brick.
Built in 1930-1, original feature of the complex.
Supplied the gas required when the retorts were started up and closed down.
The Gas Producer consists of an insulated metal furnace, six feet (1.83 m) in diameter. This structure has a light coating of surface rust and the base holding-downs have deteriorated.
Central Control Room
Built in 1979-81 as part of the rehabilitation of the plant.
Used as a control room and a lunch room.
A concrete block building. It was covered with a corrugated iron roof that has since been removed. The concrete block that remains is in a reasonable condition.
Lurgi Retort Building
Built in 1930-1, original feature of the complex.
It houses the two Lurgi Spulgas retorts which produced the semi-coke and gas that powered the rest of the plant. The retorts operated continuously, 24 hours a day, seven days a week. After being conveyed to the top of the building by the bucket elevator the slack was deposited into electrical hoppers. Subsequent processing took place in three stages. During the first stage, the drying, hot gas of about 300 degrees Celsius was forced through the slack to force out the inherent moisture. This process took about five hours. This was followed by the second step, the carbonisation. The dried coal fell through chutes into the lower section of the retorts where it was carbonised by passing through gas at a temperature of 600 - 700 degrees Celsius. This gas was subsequently directed to the Machine House for processing and cleaning. During the third phase, the semi-coke was cooled to about 200 degrees Celsius at the lowest level of the retort. From there it was discharged onto a conveyor belt and transported to the Char Crusher.
A five story steel framed structure. The upper levels were initially sheathed in brick and had four oblong windows extending from a depth of two floors on the side walls. Similar windows were located on the end walls. The building was topped with a gabled roof, broken for most of it length by a monitor. Although some of the original exterior remains, the brick cladding on the south-western half of the building as well as the corrugated asbestos roof was replaced with corrugated iron. This was carried out during the refurbishment of the plant that took place between 1979 and 1981. The building is basically a 'skin' protecting the retorts and the workers operating the machinery. It consists of two parts, the principal heavy structure that supports the hoppers and retorts and a lighter secondary structure supporting the floors, walls and roof. Some of the corrugated iron cladding is missing; otherwise the building is generally in a good condition.
Built in 1930-1, original feature of the complex.
This building housed the machinery for cleaning the raw gas after it had been directed from the Retort Building. Here the gas was passed through a pre-cooling unit where the gas was cooled down to 110 degrees Celsius. After that it flowed to a Thiessen disintegrator that removed the bulk of the tar, then through an auxiliary tar separator and finally onto the water-cooled tube coolers where the light oil was condensed. The original four condensers were placed outside the Machine House, two of which are still present. Tar oils extracted during the gas clean process was conveyed to open tanks in the Tar House. As part of the 1979-81 refit a new tar and oil recovery unit was constructed near the end of the machine house, replacing the old disintegrator. The south-western end of the building including much of the roof and wall cladding was removed to accommodate the new machinery. However, the original gas cleaning machinery remained in the north-eastern half of the building.
A metal framed building with brick in filled walls. It had a gable roof with monitor; both were originally clad with corrugated asbestos sheeting. On the north-eastern half of the roof the original cladding is replaced with fibrolite. The building is stable at present; the remaining machinery has relatively light surface rusting.
New Tar Recovery Unit
Built during the refurbishment of the plant in 1979-81.
The new tar and oil recovery unit that was constructed near the south-eastern end of the machine house. The roof and exterior wall cladding were removed to accommodate the new machinery.
The New Tar Recovery Unit is made of steel.
Built in 1930-1, original feature of the complex.
Here tar from the gas cleaning process was collected in open tanks set in the ground. From there tar was pumped to large tanks near the Tar Distillation Plant where it was stored before further processing.
Low, partly underground building with concrete walls that extend about half a metre above ground level. The walls of the gable ends are brick clad. The gable roof is broken by a central monitor made of brick with a corrugated steel roof. The monitor has three small windows on each side. The structure seems to be in reasonable condition.
Oil Tar Tanks
Later addition to the plant, date of installation not currently known.
This is where tar was stored before it was to be processed in the distillation plant.
This structure consists of metal tanks covered by a gable roof clad with corrugated iron supported by metal support posts. The tanks are situated in an open metal container preventing spillage in case the tank is damaged or starts leaking. The building and tanks are in reasonable condition.
Old Tar Distillation Plant
Built in 1930-1, original feature of the complex.
This building originally housed two pot stills where pitch required in the binder process was produced from the tar that was a by product of the coal drying process. These stills held 10 tons each.
The building housing the tar distillation plant is a tall, iron framed structure with brick cladding. The tallest section has a medium gable roof, the other three sections have shed roofs, one of which has since been removed. The roof and part of the exterior is now clad with corrugated iron. The structure seems to be in a reasonable condition. Some of the relatively light steel framing is rusting below water level.
Built in 1930-1, original features of the complex.
Part of the original Tar Distillation Plant; they are located to the north-east of the building. As the name suggests, these were used to cool the pitch after the distillation process.
The Pitch Coolers are made of steel.
Added in 1938, replacing the old tar distillation plant.
After the pot stills had become seriously corroded by 1937 the original tar distillation plant was replaced with a Wilton continuous pipe still. This still was capable of treating 105 gallons (477.34 litres) of tar per hour and could produce either pitch or distillate, the latter being used in the production of creosote.
The Wilton plant was housed in an extension of the Old Tar Distillation plant building. This was little more than an open shelter added to the rear of the building. The shelter consists of a gabled roof made of corrugated iron on iron supports.
Char Crusher aka Semi-coke Crushing and Screening Plant
Built in 1930-1, original feature of the complex.
This was where the semi-coke was transported to after having been processed in the retort building. Originally this building housed a roller crusher. However, the hard and abrasive semi-coke caused uneven wear on the roller. As a result, the crushing equipment was replaced at an early stage by a hammer mill. At the same time a vibrating screen was installed. This separated the finer material that was fed directly into the coke bunker adjacent to the carbonette building. The remaining larger material was crushed in the hammer mill before being conveyed to the coke bunker. During World War Two another screen was installed. This separated anything over 3/16” (0.48 cm) which was subsequently sold as 'Waicarbo', a fuel for gas-producer driven motor vehicles. After World War Two this was replaced by 'Raycarbo', larger-size fuel (> 12 mm) used in slow-combustion stoves, space heaters and domestic water heaters.
Only a lower section of wall of the crushing plant remains today. Based on that it seems to have been a steel framed brick clad building. Little of the fabric of this building survives and the remnant wall is in a poor condition.
Built in 1930-1, original feature of the complex.
This building is where the carbonettes were produced. Crushed carbonised coal was transported to this building from the coke bunker by means of an enclosed conveyor. Once inside, the crushed coal was mixed with a binder of coal tar pitch or bitumen. This substance was subsequently heated and delivered to the steel-framed carbonette presses that produced the egg-shaped carbonettes. From here they were transported by a water sprayed conveyer to the carbonette bunker.
The carbonette plant is an iron framed building infilled with a single skin of bricks laid in stretcher bond. The gabled roof, which is clad with corrugated asbestos roofing material, is broken by a centrally located monitor. The monitor is clad in corrugated iron. The building is generally in a reasonable condition. However, the steel is not particularly heavy and is suffering from rust where it is below water.
No 2 Control Room
A later addition to the plant since it does not show on the 1941 aerial photo, the 1951 insurance plan or the 1974 plan. It is therefore likely that this was added as part of the 1979-81 rehabilitation of the plant.
This building functioned as a control room for the plant.
The No 2 Control Room is a free standing wooden framed building with fibre cement cladding. It has a gabled roof clad with corrugated iron. The structure seems to be in reasonable condition.
Built in 1930-1, original feature of the complex.
The building where the crushed carbonised coal was stored before it was transported to the carbonette plant where it would be used to produce the carbonettes. The storage capacity of the bunker is 250 tons. This building is located adjacent to the carbonette plant at its north-eastern corner.
The bunker is a free standing metal framed structure. At the third storey level the frame is clad in sheet metal and corrugated iron. The bunker has a gabled roof covered with corrugated iron. The coke bunker seems to be in a reasonable condition.
Built in 1930-1, original feature of the complex.
After the carbonettes were produced they were conveyed to one of two carbonette bunkers. The turn station was placed at the end of the water sprayed conveyor. The turn station provided conveyance either to the left, where the No 1 carbonette bunker used to be located or to the right, where the No 2 carbonette bunker is situated.
This is a small corrugated iron clad shelter with a barrel-shaped roof. It stands on tall, braced iron uprights. The steel above the ground beam is in reasonable condition although much of the cladding is missing.
No 2 Carbonette Bunker and Screening Plant
Constructed in 1933 in addition to the first carbonette bunker to increase storage capacity for carbonettes for the drying process.
Carbonettes delivered by conveyor to the top of the building were diverted to one of the two drying floors the structure housed. There they were left overnight to cool down. After cooling the carbonettes tumbled down the inclines on either side to be released through chutes located at regular intervals along the external side walls. These could be opened manually to release the carbonettes into railway trucks situated on the rail sidings under the chutes. Dust or fragmented carbonettes fell through the cooling floor battens to the ground under the structure.
The carbonette bunker is a double floored cooling structure and screen. It has an open timber framework comprised of 7” x 7” (17.78 x 17.78 cm) upright posts on concrete piles. It features diagonal bolted bracing (8” x 4”) (20.32 x 10.16 cm), 6” x 4” (15.24 x 10.16 cm) and 6” x 6” (15.24 x 15.24 cm) struts and 3” x 1” (7.62 x 2.54 cm) timber battens spaced 1” (2.54 cm) apart clad the wall and the floors. The gable roof is broken by an open sided monitor and is sheathed with corrugated asbestos. The roof line extends well beyond the side walls (7'6”) (228.6 cm) and is supported by struts which connect to a beam that runs the length of each exterior wall. Generally speaking the building is in reasonable condition. However, several timber beams have been removed after the plant was shut down. Since the structure is sufficiently redundant and has little load in it, it is not in danger of collapsing. Some of the remaining timber beams have been infected with borer. This possibly caused the collapse of a small part of the southern end of the building. Additionally, the bases of some of the wooden supports have rotted away. In the past this problem has been remedied by splicing in new sections. However, some of the original wooden supports are still decaying.
Built around 1940 at the same time the second screen was installed in the Semi-coke Crushing and Screening Plant.
This building was initially used to store the 'Waicarbo'. After World War Two 'Raycarbo' was stored here. Both were delivered from the Crusher building by conveyor and from here loaded into railway wagons by means of a simple iron chute.
This open sided shelter is little more than four iron uprights supporting a gable roof. The supports for these uprights were created by filling four forty-four gallon (200 l) drums with concrete. The drums were subsequently removed leaving concrete pillars. A corrugated iron roof, broken by a louvered monitor also clad with corrugated iron, covers the timber rafters. This building is in a poor condition, having never been particularly well built with the uprights lacking any bracing.
Storage Tanks and Creosote Shed.
These tanks are located on higher ground at the south-eastern end of the plant. Some of these are original; others are later additions.
These tanks were used to store creosote. The purpose of the shed is not clear.
Two types of tanks are located here. There are thirteen large drum-shaped tanks lying on their sides. They are made of steel and all connected with each other and the plant by means of steel piping. In addition there are eight round structures, also made of steel. These are of a similar model as the later Tar / Oil tanks elsewhere but of a smaller size. The shed is a simple square building with a wooden frame; the walls are clad with corrugated iron. It has a simple shed roof also covered with corrugated iron. The condition of the tanks is unknown.
Creosote Tank Tap
Probably a later addition to the plant since it does not show on the 1951 insurance plan. It does however, show on the 1974 plan.
This is where the forty-four gallon (200 l) drums were filled.
A steel construction. Because the area has been completely covered by gorse this structure has not been assessed in recent years.
Tar / Oil Tanks
Later additions to the plant. They are not shown on the 1951 insurance map, but do show up on the 1974 plan. Therefore, they have probably been added sometime during this period.
These tanks were used to store tar and creosote. Creosote was a by-product of the tar distillation process and sold to the Forest Service for use in its timber treatment plant. Some creosote was also sold on the local market.
These are large round structures made from steel with iron roofs. They seem to be in a reasonable condition.
Conveyor Belts between Structures
Most have been built in 1930-1 as part of the original construction of the plant; a few have been added later as more buildings were erected on the site.
The function of these was to convey raw materials, partly processed slack coal or finished products from one part of the plant to another for further processing or storage.
The conveyors are made of steel; some are partly or wholly covered with corrugated iron. The condition of the various remnants of lengths of conveyor belt varies greatly. Some parts are in good condition, bar missing some of the cladding, other parts are in very poor condition, not only having lost the cladding, but also having collapsed to the ground, covered in rust.
The current building was probably erected in the late 1940's early 1950's, allegedly replacing an earlier bathhouse at the same location. However, nothing is visible at this location on the aerial photograph taken in 1941.
An auxiliary building associated with the carbonisation plant. This provided a place where the workers could get cleaned up and changed after their shifts ended.
The bathhouse is a timber framed building set on a concrete pad. The frame is clad with fibrolite fixed with galvanised flashings. It has a gabled roof, clad in corrugated asbestos, which is broken by a central monitor. The monitor features six light windows with pivotal sashes. After it had been built a false ceiling was put in which would have thwarted ventilation through the windows. Above this false ceiling the earlier electric light can still be seen. Squat, six paned windows located around the building just below the eaves allowed in light without compromising privacy. Inside, it had a centrally located shower partitioned into two bays fitted with a total of 16 shower heads. Water was provided from an elevated cistern at the south-eastern end of the building. Simple timber seating and bays of lockers ran around the external walls. At each end of the bathhouse a simple cast iron stove was installed providing warmth. The bathhouse is in variable condition. Some of the timber parts of the building are still sound, other parts have been infested by borer or are rotting away.
The existing boiler house was probably built in 1949-50, replacing the original one from the early '30's.
This building housed two Babcock and Wilcox steam boilers that provided steam for the entire plant, including the bath house.
The walls are structural, brick laid in garden wall bond, in contrast to the brick sheathing on an iron frame characteristic of the buildings originally built in the early '30's. The four corners of the building are defined by a brick pier. A concrete bond beam runs along the top of the walls. It is covered by a gable roof sheathed in corrugated steel which has also been used as cladding for the gable ends. This structure is in a reasonable condition.
a German plant using the low temperature Lurgi carbonisation process was ordered from the Lurgi Metallgesellschaft, Frankfurt, Germany.
1930 - 1931
arrival of the plant on the Ruahine and start of the construction.
1979 - 1980
Complex partially upgraded.
Plant was closed permanently
1991 - 1995
a first clean-up was carried out, a bund was created to protect the Awaroa stream, part of the plant was demolished as a result.
1992 - 2001
expansion of the adjacent opencast mine destroyed the nearby Rotowaro Industrial Precinct and part of the Carbonisation Works.
Brick, concrete, fibrolite, steel, corrugated iron, asbestos, timber.
Public NZAA Number
11th November 2009
Report Written By
F. van der Heijden, G. Henry
Wood, Brian, The Heritage and Environment of Coal Gorge and the Brunner Suspension Bridge, Greymouth, 2004.
Len Richardson, Coal, Class and Community: The United Mineworkers of New Zealand, 1880-1960, Auckland, 1995
D. Allardice and B.C. Young, Utilisation of Low Rank Coals, 2000
A. Stranges, 'Germany's synthetic fuel industry, 1927-1945', in John E. Lesch, The German Chemical Industry in the Twentieth Century, Springer, 2000
A fully referenced registration report is available from the NZHPT Lower Northern Area Office. A copy of the registration report from the original registration completed on 22 August 1991 is also available, on request.
Please note that entry on the New Zealand Heritage List/Rarangi Korero identifies only the heritage values of the property concerned, and should not be construed as advice on the state of the property, or as a comment of its soundness or safety, including in regard to earthquake risk, safety in the event of fire, or insanitary conditions.