Rating Manual section 6 part 3: valuation of all property classes

Section 220: cement works

This publication is intended for Valuation Officers. It may contain links to internal resources that are not available through this version.

1. Scope

1.1 This section applies to industrial plants used for the manufacture of cement.

2. List description and special category code

List description: Cement Works and Premises IF2

SCAT code: 052, Scat suffix V

2.1 Cement manufacture industry

History of the industry

Probably the earliest example of the use of cement was in the building of the Egyptian pyramids where lime was used as a bonding material. Later the Romans produced a cement that was based on finely ground volcanic materials and which had the property of setting under water. In the 18th century Blue Lias lime, which has a clay content was also found to set under water. Developments in cement manufacture continued and attempts to make a cement similar in colour and texture to Portland stone were well advanced by the beginning of the 19th century but it was not until 1840 that at the Swanscombe works in Kent what is known as Portland cement was manufactured using the chalks and clays of the neighbourhood. Subsequently when it was established that Portland cement could be equally well made from limestone mixed with clay or shale the industry developed where those materials could be found.

In the latter part of the 19th century the invention of the ball-mill and the tube-mill transformed the grinding of the raw materials. From 1900 the static kilns originally used were gradually replaced by inclined rotary kilns which then increased in diameter and length until the late 1960s when dry process works were constructed using preheater towers where the kilns were of larger diameter but much shorter length. The early rotary kilns had outputs around 50 tons/day; nowadays outputs of 2,000 tons/day are achieved and this increased output has given rise to greater efficiency throughout the industry and also in the winning and transport of the raw materials.

A major pollution problem facing the industry is that of dust. It occurs at almost every stage of manufacture, being produced during the preparation of the finely ground raw materials, in the pre-heating and burning stages, in the final grinding of the clinker, in the grinding of coal when this is used as a fuel and is also released at the conveying and packing stages.

Public pressure for environmental control has led to legislation and the industry is subject to inspection by Inspectors of Environment Agency. In consequence the industry has found it necessary to install extremely costly plant in the form of cyclones or, more commonly electrostatic precipitators in order to minimise dust emission.

2.2 Cement works process

The object of cement manufacture is to convert chalk, marl or limestone into cement for use in the civil engineering and construction industries.

The basic process is to mix calcareous materials (limestone, dolomites and chalk) with silica and alumina (clay or shale) which are first calcined and then burnt in rotary kilns at a temperature of 1350°C. The chemical reaction at this heat fuses the particles into nodules termed clinker which when cool is ground to a fine powder; gypsum is added at this stage to control the eventual setting time. Coloured and other cements are produced by various additives at the grinding stage.

The principal methods of production in the UK are:-

a.Wet

b.Semi-wet

c.Semi-dry

d.Dry

High alumina cement is produced at only one works in the UK and being of a highly specialist nature it is not covered by these instructions.

The diagram Appendix 1 shows the stages involved in these processes, and the production flow chart Appendix 2 at the end of this section together with the Guide to Referencing referred to in 6.1 should be studied in conjunction with this paragraph.

2.3 Section A - raw material preparation: semi-wet and wet processes

Chalk or limestone is conveyed from the quarry face to a reception point or directly into a roughing mill which breaks the material down. Water is added to form a slurry which may then pass to a wash mill for further mixing. In some works the blending of chalk and clay slurry takes place in ‘doctor’ tanks.

From the washmill or blending tanks the slurry is pumped either to open basins for storage or to the feed end of the kilns.

To prevent sedimentation in the tanks the slurry is agitated by either mechanical means or by compressed air.

In some works, the initial preparation of slurry may take place at the quarry and be conveyed by pipeline to the cement works.

2.4 Section B - raw material preparation: semi-dry and dry processes

The raw material, usually limestone, is considerably harder than chalk and therefore has to be broken down to a fine powder by means of ball, tube or compound mills where the pressure for grinding is generated by gravity with falling balls.

The constituent materials (limestone and shale) are ground to a powder and blown through tubes to reinforced concrete blending bunkers containing compartments enabling each material to be stored separately. The materials are then drawn off through a controlled system in the required proportions and fed to the raw meal silos. At least two raw meal silos are required so that one may be filled and agitated to thoroughly mix the meal, while the other is being emptied.

The raw meal then passes by enclosed conveyor or tubes to the preheater section before entering the kiln.

2.5 Section C - burning: wet process

The slurry is pumped from the washmill, blending or storage tanks and introduced into the feed or upper end of the kiln. The rotary kiln is a large cylindrical steel shell lined with refractory brickwork mounted at an inclination of about 1 in 30 to the horizontal on a number of roller supports so that it may be rotated about its axis at about 1 rev/min. Firing is by pulverised coal, oil or gas injected at the lower end.

The slurry on entering the feed end encounters the hot gases which boil off the water. A curtain of chains is hung in the drying zone which become coated with the slurry and assist in heat transfer by offering a large surface to the gas stream.

The raw materials leave the chains as small pellets and enter the calcining zone where the temperature rises past 800°C and carbon dioxide commences to be driven off. The movement of slurry down the kiln is assisted by a system of festoon chains.

Finally the material reaches the burning zone, comprising about one-fifth the length of the kiln with a temperature of about 1350°C; at this temperature the chemical reaction occurs that fuses the material into clinker.

The kilning cycle can take several hours.

At the discharge end of the kiln the temperature of the clinker will have fallen slightly below burning temperature to about 1100°C. Provision is made to cool it to a handling temperature of about 50°C either in radial coolers integrated with the kiln, rotary coolers which are similar in construction to a kiln or in box or Fuller Grate coolers. The air used for cooling becomes heated in the process and is fed to the firing end of the kiln to assist in the combustion of the fuel.

The cooled clinker is conveyed to a store to await grinding (Section D). Storage is usually in steel silos (heat could damage concrete silos).

2.6 Section C - burning: semi-wet process

In this process as much water as possible is removed from the wet slurry by filtering. This is most commonly done in the UK by use of a filter press. This method involves pressing the slurry between plates carrying filter fabric. The resultant cake is cut to nodule size and fed to a grate preheater of the Lepol type or introduced directly into the kiln which may be shortened in the drying zone.

While none at present operate in this country, another method is to remove the remaining moisture after filtering in a preheater utilising hot gases from the kiln. By eliminating the drying zone completely a much shorter kiln is needed and the material already partially calcined is fed directly into the calcining zone.

2.7 Section C - burning: semi-dry process

In this method the material is pre-heated before entering the kiln which has only two zones (calcining and burning) thus reducing its length by nearly half.

The dry meal is conveyed from the blending silos to a nodulizer (a flat pan rotating in an inclined plane) in which the meal is dampened and pelletised before passing into the Lepol grate (a long arch-shaped refractory brick lined structure with a travelling grate) which partly calcines the pellets before they enter the kiln.

The pellets then follow the same path as for the wet process.

2.8 Section C - burning: dry process

The dry meal is conveyed from the blending silos and fed into the top of a pre-heating system (Humbolt or Dopol) which consists of a series of cyclone chambers through which the meal passes and in its passage meets the hot gases rising from the kiln. The temperature of the meal rises rapidly during its descent to about 800°C and the particles partly calcine before entering the kiln.

The kiln has two zones (calcining and burning) and is of shorter length than those used in the wet process.

The particles then follow the same path as for the wet process.

2.9 Section C - dust control

In both the wet and dry processes electrostatic precipitators are used to extract dust from the kiln gases and return it to the process. These are found at the feed end of the kiln and usually take the form of large rectangular steel chambers although in some works smaller cylindrical type units are found. Dust-laden gas enters the precipitator and passes between electrodes and earthed collecting plates, where the discharge between them causes the dust to be deposited on the plates; it is then collected and returned to the process.

In more modern works with high output kilns precipitators may also be found at the cooling stage.

2.10 Section D - grinding

The buildings and plant used in the grinding of the clinker are similar for all processes. The clinker is conveyed from the clinker store mixed with gypsum (usually about 5%) and ground to a fine dust in large rotary ball, tube or compound mills.

2.11 Section E - storage, packing and despatch

The cement on leaving the mills is conveyed, usually by pneumatic means, to silos which are part of or adjacent to packing plant buildings in which the cement is bagged or bulk loaded into road vehicles or rail wagons for distribution.

2.12 Allied production units

Specialised products such as Snowcrete, Whiting, lime and coloured cements are manufactured in plants which are broadly similar to those already described. These and other allied works within the curtilage of the main works should be valued in accordance with the principles outlined in this Section.

2.13. Trade depression

Until the early 1970s the demand for cement was such that the industry found difficulty in satisfying it, but since then rationalisation has taken place and coupled with recessions in the construction industry, have led to the closure of smaller works. Claims for trade depression should be dealt with in accordance with Section 4: Part 3.

3. Responsible teams

3.1 The valuation and referencing of this class of property is the responsibility of the Industrial and Crown Team within the National Specialists Unit (NSU).

4. Co-ordination

4.1 Responsibility for ensuring effective co-ordination lies with the NSU Industrial and Crown Team.

Rateability of rotary kilns

British Portland Cement Manufacturers Ltd v Thurrock UDC 1950 cA 43 R & IT 841.

Tunnel Portland Cement Co Ltd v Thurrock UDC and Spencer (VO) 1951 LT 44 R & IT 632.

Jones (VO) v Rugby Portland Cement Manufacturers Ltd 1952 LT 45 R & IT 807.

Rateability of rotary coolers

Gilmore (VO) v British Portland Cement Co Ltd 1957 LT 50 R & IT 129.

It should be noted that the above cases concerning kilns and coolers were decided under the 1927 Plant and Machinery Order. See the relevant Practice Note to determine rateability of these items.

Pipelines

English Clay Lovering Pochin& Co Ltd v Davis (VO) 1966 LT RA 475.

Rugby Portland Cement Co Ltd v Hunt (VO) 1969 LT RA 496.

Air Products Ltd v Case (VO) 1970 LT RA 50.

Russell (VO) v Shell-Mex& BP Ltd 1972 LT RA 65.

Petrofina (Great Britain) Ltd v Harrington (VO) and Hurst (VO) v Shell-Mex& BP Ltd 1973 LT RA 65.

BP Refinery (Llandarcy) Ltd v W G Edwards (VO) 1974 LT RA 1.

6. Survey requirements

6.1 Guide to referencing

A guide to the referencing of cement works is held by the NSU Industrial and Crown Team.

6.2 Plant and machinery

Cement works and allied production units contain a considerable number of items of plant and machinery named in the Valuation for Rating (Plant and Machinery) Regulations. Rateability should be tested in accordance with the principles set out in Section 6: Part 5.

Major items for consideration include kilns, coolers, precipitators, wash plant, storage tanks, silos, Lepol grates (semi-dry works) and Dopol pre-heater system (dry works).

By the application of exception (c) of the 1960 Order (as amended), and subsequently of the 1989 Regulations, major parts of rotary kilns and coolers ceased to be rateable as from 1 April 1974.

However the Valuation for Rating (Plant and Machinery) Regulations 1994 and their replacements, The Valuation for Rating (Plant and Machinery) (England) Regulations 2000 SI 2000 No. 540, and The Valuation for Rating (Plant and Machinery)(Wales) Regulations 2000 SI 2000 No. 1097 2000, do not contain an equivalent to exception (c) and hence the majority of kilns may be rateable if they have a cubic capacity in excess of 400 cubic metres; see the relevant Practice Notes for details. The kiln is the heart of any cement works and its type, capability and performance enables the works to be appraised as an entity and the information set out in the Guide to Referencing should continue to be obtained.

7 . Survey capture

7.1 Rating surveys should be recorded manually in binders held by the NSU Industrial team.

8. Valuation approach

8.1 Method of valuation

Cement Works are highly specialised hereditaments rarely, if ever, let and the appropriate method of valuation is the contractor’s basis (see Section 4 Part 3).

Where hereditaments include a mineral element the Mineral Valuer (MV) will advise on the value to be attributed to the mineral element.

8.2 Unit of assessment

The unit of assessment should be ascertained in accordance with general rating principles.

Close liaison is necessary with the MV responsible for the valuation of workings or quarries contiguous to or associated with the cement works. Where not self evident, the parts of the property to be valued by the MV should be discussed and agreed.

8.3 Site

The site should be valued in accordance with the general principles set out in RM 4:7. Cement works were originally established close to the source of raw materials and are therefore often sited in rural locations remote from other industry.

The presence of road and rail communications, sources of labour, the continuing availability of a ready source of raw materials and access to markets for the finished products are all matters which must be weighed in the valuation.

8.4 Unit of comparison

Broad methods of comparison are based on kiln capacity and include:

a. Rated output

b. Actual output

c. Notional output

Rated output denotes the designed optimum output. Experience has shown that this is often difficult to obtain and sometimes unreliable because of the variation of factors taken into account in its calculation as between one works and another.

Actual output although usually more readily obtainable is affected by factors which may not properly be taken into account in the valuation.

Notional output broadly accords with actual optimum output. It is a method of comparison devised by adopting a unit of output of clinker tons per annum which, applied to the ARC of the whole hereditament, or to specific sections thereof produces a comparative unit of ARC per clinker ton. It also affords a means of testing actual output.

9. Valuation support

9.1 Valuations for cement works are held on the Non-Bulk Server (NBS).

Practice note 1: 2017: cement works

1. Market appraisal

According to statistics supplied by the Mineral Products Association, production of clinker and cement in Great Britain has fallen between the pre AVD calendar years of 2007 and 2014. Cement Sales, which include imports, have fallen by a similar proportion. The relevant tonnages are:

Year

Clinker Production

Cement Production

Imports

Cement Sales

% Imports

2007

10,228,000

11,887,000

1,376,000

13,026,000

10.56

2014

  7,197,000

  8,958,000

1,817,000

10,568,000

17.19

Change

    -29.63%

    -24.64%

   +32.05%

   -18.87%

 

Although demand for Cement has fallen, three older, high cost, wet process works were taken out of production after 01 April 2008. Two of these have been partially or totally demolished and there is no intention to re-open the third. These works produced just over 2,000,000 tonnes of clinker in the 2007 calendar year.

2. Changes from the last practice note

The Practice Note for the 2010 Rating List covered Responsible Teams, Co-ordination, and Special Category Code which are now dealt with in the Rating Manual section for the class.

3. Ratepayer discussions

There have been no discussions with the cement industry.

4. Valuation scheme

There is no scheme of valuation as Cement Works are valued by a limited number of specialist caseworkers who are part of the Industrial and Crown Team of the National Specialists Unit. The properties will be valued using the Contractor’s Basis of Valuation with the majority of costs being derived from the Valuation Office Cost Guide. Costs of more specialist items, which are particular to Cement Works, and are not the subject of Cost Guide entries, will be provided separately. Allowances have been made in previous Rating Lists to reflect differences in the variable costs of producing Clinker and these will be reviewed to take account of any changes in their relativity at 01 April 2015.

Practice note 1: 2010 - cement works

1. Co-ordination

1.1 This is a Class dealt with by National Specialists Unit – Industrial Team.

1.2 Responsibility for ensuring effective co-ordination lies with the Specialists within the NSU-I.

1.3 For further information see Rating Manual - section 6 part 1: Practice Note 1 : 2010.

1.4 The R2010 Special Category Code 052 should be used. As a NSU Class the appropriate suffix letter should be V.

2. Valuation guidance

2.1 The valuation of cement work hereditaments is the responsibility of NSU-I in Leeds.

2.2 For the 2010 Revaluation the NSU-I will notify all Business Units of the appropriate RVs to be entered into their Local Rating Lists.

Appendix 1: 2010: cement works

Cement works stages involved in the principle processes of manufacture

Appendix 2: 2010: cement works

Production flow diagram

Appendix 3: 2010: cement works

Production sections

Referencing Prefix Letter

Production Section

Included Buildings and Plant

A

Raw Material Preparation (semi-wet and wet processes)

Tipplers

Crusher Houses

Rough Mills

Screening Mills

Mixer Tanks

Slurry Storage Tanks

B

Raw Material Preparation (semi-dry and dry processes)

Raw Material Stores

Crusher Houses

Tube Mills

Blending Silos

Raw Meal Storage Silos

C

Burning Plant

Chimney Stacks – Flues

Precipitators

Rectifier Houses

Raw Meal Nodulisers

Pre-Heating Plant (Lepol Grate, Humbolt or Dopol Systems)

Kilns and Coolers

Kiln Houses

Fuel Plant, Coal Stores

Oil Tanks etc.

D

Grinding

Clinker Stores

Grinding Mills and

Mill Motor Houses

Compressors and

Compressor Houses

E

Storage, Packing and Despatch

Storage Silos

Packing Plant Buildings and

Despatch Docks

Warehouses

Wharves

F

Not allocated

G

Snowcrete

Completed Production

Unit (as for cement)

H

Whiting Plant

Complete Production Unit, which includes Washmills, Slurry and Settling Tanks, Drier Houses Storage, Packing and Despatch

J

Coloured cements/Snowcem

Mixing Mills

Storage, Packing and Despatch

L

Lime Plant

Complete Production Unit which includes:-

Lump Lime Storage

Hydrating Plant

Storage, Packing and Despatch

K

M

Not allocated

N

P

Administration

Offices (other than process control)

Despatch Offices

Weighbridges

Staff Welfare Facilities

Laboratories

Q

Maintenance

Workshops

Stores

Transport Garages

Facilities