Evolution of the Biocentre Process

The History 

 

Background 

 

Thermal treatment of raw wastes entered the waste management hierarchy in the UK one hundred and forty years ago 
with the construction of the first municipal incinerator in Nottingham. These early incinerators were extremely 
primitive, consisting of a series of combustion cells that were loaded manually with mixed municipal wastes. Upon 
completion of combustion resulting fused and toxic slag in the cells had to be removed by manual raking before a new 
charge could be loaded. There was no treatment of the exhaust emissions – they were simply exhausted to atmosphere 
via chimneys. 

 

The early plant became superseded by mass burn units where the exhausts were cooled in spray towers in an attempt 
to remove as much of the fly ash as possible. However, the plants were still inefficient and wasteful, in that none of the 
heat from combustion was recovered. This issue was later addressed by delivering the hot gases from combustion to 
specially designed boilers, where the steam could be used for district heating and electrical power generation.  Plants 
of this type replaced the early mass burn units and became common, but increasing environmental regulation required 
an almost continual process of modifications to reduce or eliminate pollutant emissions to atmosphere (Dioxins, 
Furans, toxic fly ash) and to ground (bottom ash and furnace slag). 

 

Although the heat recovery incinerators enjoyed popularity for many years, the steady increase of recycling initiatives 
began to have an adverse effect upon them. As more and more of the higher calorific fractions were recovered, the 
calorific value of the residual fractions going to incinerators reduced, generally to a level of around 9.5 MJ/kg. At that 
level the residual wastes are hardly combustible, and they frequently required the assistance of supplementary fuels to 
improve combustion. This dramatically reduced the efficiency and economic viability of plants generating power or 
supplying district heating.  In some plants an attempt was made to screen out the materials that were detrimental to 
combustion (mainly organics and inerts such as glass and soils), and to thereby increase the calorific value of the 
remainder. That, however, left the problem of how to dispose of the screened out fractions, and while aerobic 
digestion was possible and was implemented, the resulting product was too contaminated for use as a compost. It 
could only be landfilled, thereby limiting the value of incinerators as a disposal route. 

 

Development of the UK MBHT Process For Fuel Production 

 

In the late nineteen-seventies, in an attempt to find an alternative to incineration, the concept of using the wastes as a 
raw material for a solid fuel that could be consumed in industrial boilers was conceived, under the generic title of 
Waste Derived Fuel (WDF). Five plants were built – four sponsored by the Department of the Environment and one 
commissioned independently by East Sussex County Council (ESCC). The DoE plants were of a common design, but they 
suffered from their being unable to effectively separate contaminants from the fuel products, and they were not a 
commercial success. The ESCC design was fundamentally different, and the fuels it produced were of a much higher 
quality and calorific value. The ESCC design incorporated Mechanical Biological and Heat Treatment (MBHT) stages. The 
fuel products produced found ready markets at attractive prices in power stations and industrial consumers, to the 
extent that the plant did not have the production capacity to satisfy the demand.  

 

The ESCC MBHT plant was successful largely because it was designed according to a different philosophy. The early DoE 
plants were simply seen as a means of disposing of wastes, with the products being almost an afterthought. However, 
the engineers who designed the ESCC plant (Tony Manser and team) took the approach that if the plant was going to 
be of value to waste management, then it should be seen to be a commercial producer of a value-added product for 
which the raw material happened to be wastes. The design philosophy targeted product quality and not waste disposal. 
The process was designed to eliminate contaminants to the greatest extent possible. As a result the calorific value was 
much higher because the process removed the non-combustibles and contaminants at several stages, reducing the ash 
contents to similar to those of coal, and also reducing the moisture content to less than eight percent. This created a 
fuel that was made almost entirely out of paper and card, with some wood, plastics, and traces of textiles.  

 

 

Evolution 

 

This MBHT technology then evolved through a series of five plants, further improving the separation and treatment 
processes without major changes to the original design, and employing increasing levels of automation culminating in 
the two large fully automated plants built for Slough Heat & Power and Castle Cement in 2003 and designed by 
Advanced Recycling Technologies (ART) Ltd founded by Tony Manser and others in 1991. The intellectual property of 
ART was acquired by Biocentre Technologies Ltd in 2012 with the intention of developing a series of MBHT process 
plants throughout the UK. 

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A fuel production plant built by ART in 2003 – processing 230,000 tonnes a year of wastes with no atmospheric 
emissions. 

 

While the calorific value of the products is important, the removal of inert contaminants is equally so. 
The only boilers in which one can burn raw wastes or low-grade waste derived fuels (WDF) are those specifically 
designed for incinerators, and they are very different from conventional boilers. If one tried to burn those materials in 
an industrial boiler it would destroy it in weeks. Superheaters clog up with fused ash and suffer from massive high 
temperature tube erosion that can reduce a tube thickness by several thousandths of an inch a week — which means 
the tubes burst in about three months of service. Gas pass tubes also suffer badly from grit erosion, and those in the 
furnace are attacked by flame erosion since the flame length from crude wastes is much longer than from conventional 

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fuels. Since the chloride and Sulphur contents in raw wastes and low grade WDF are high, boiler air heaters in the 
exhaust gas passes suffer from condensation of hydrochloric acid, and the Sulphur combines with moisture at 
temperatures below 250°C to form Sulphurous acid which, being unstable, breaks down into Sulphuric acid.   

 

Crude wastes and low grade WDFs also contain high levels of silicates, and these fuse on boiler tubes in the high 
temperature zones. Because they fuse at lower temperatures than the rest of the fly ash they migrate to the tube 
surfaces. Silicates (sand) were once used by blacksmiths when welding iron together by forging, because silicates have a 
fluxing property. Meanwhile, boiler tubes always have a rust coating, but once that is established it protects the tube 
from further corrosion. The silicates flux that away, allowing the acidic flue gases to once more attack the tubes every 
time the soot blowers are operated, and again leading to tube failures in months. 

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Dioxins and furans 

 

There is also the issue of dioxins and furans (Polychlorinated Dibenzodioxins and Poly chlorinated Dibenzofurans) with 
which conventional boilers cannot deal. These are not manufactured products, but they do arise from a number of 
sources, including municipal incinerators, forest fires, coal-fired power stations, and many other natural and man-made 
combustion processes. 

 

The EU Waste Incineration Directive (WID) require boilers burning wastes or low grade fuel to maintain an exhaust gas 
temperature of 250°C in order to prevent dioxins and furans from reforming. Industrial boilers are trying to get the 
maximum amount of heat energy possible from fuels, rather than heating the local atmosphere. In many incinerators 
this issue is addressed by using oil-fired after burners in the exhaust gas passes, but that rather defeats the object of 
burning waste derived fuel in the first place. Fuels made in the Biocentre MBHT process are sufficiently free from 
contaminants, and in the next generation of plants no longer include plastics, so that they do not create dioxins or 
furans in measurable quantities. This was demonstrated as long ago as 1985 by the then Associated Heat Services Ltd  
in the first of their combustion plants to use the fuel, where tests for dioxins and furans did not discover detectable 
quantities of either. 

 

The sophistication of the Biocentre process, and its ability to remove contaminants including heavy metals, is such as to 
offer the treatment of a wide range of wastes including household wastes without any need for any separation at 
source. This is a potentially important contributor to the reduction of waste management costs that have been growing 
exponentially for a number of years. It has been achieved by many years of research and development by ART Ltd and 
later Biocentre Technology Ltd, leading to the creation of mathematical modelling computer programs and data bases 
that permit processes to be designed with confidence. 

 

In recent years the desire to reduce the reliance upon fossil fuels and to substitute renewable low carbon footprint 
biofuels in their place has led to a growing interest in how waste materials could be exploited. This has resulted in the 
WRAP (Waste and Resources Action Programme) classification scheme for biofuels derived from wastes. In this scheme 
there are five classes established according to the pollution potential, metals, ash, moisture and heavy metals contents, 
ranging from Class 1 (best) to Class 5 (worst). The position of Biocentre fuel products in this classification scheme are 
shown in the table below: 

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Biocentre fuel “BC17”  * 

 

Component                                WRAP Limit                     WRAP Class 

Biomass content                       >80%                               Class 1-2 
Net CV                                        >15 MJ/kg                      Class 1-3 
Moisture content                      <10%                                Class 1 
Chlorine content                       <0.1 %                              Class 1 
Ash content                               <10%                                Class 1 
Bulk density                              >650 kg/m3                   Class 1 (optional) 
Mercury content                      <0.02 mg/MJ                 Class 1 
Cadmium content                   <0.1 mg/MJ                    Class 1 
Sum of heavy metals              <15 mg/MJ                     Class 1 

 

Biocentre fuel “BC12”   ** 

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Component                              WRAP Limit                      WRAP Class 

Biomass content >90% Class 1 
Net CV >10 MJ/kg Class 3-4 
Moisture content <20% Class 3 
Chlorine content <0.6 % Class 2 
Ash content <20% Class 2 
Bulk density >650 kg/m3 Class 1 (optional) 
Mercury content <0.02 mg/MJ Class 1 
Cadmium content <0.1 mg/MJ Class 1 
Sum of heavy metals <15 mg/MJ Class 1 

 

NB. 

 

* Biocentre BCV is the most highly refined biofuel developed from the historical and evolved processes. 
** Biocentre BFB is created by an additional process developed in 1986 to convert the organic fractions of wastes 
into washed peat-like fuels. 

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MBHT – Mechanical, Biological and Heat Treatment 

 

MBHT is the generic term for the processing technology developed by Tony Manser and associated engineers. It is a 
sophisticated form of Mechanical and Biological Treatment (MBT) of wastes which includes fuel refining stages, 
including a flash dryer. The specification and quality of the output fuel is closely controlled – and achieves the high 
levels of performance quoted above which allow the fuel to be used as a direct replacement for washed singles coal or 
wood pellets / chips. Biocentre uses its proprietary version of MBHT.