For the cement industry
Why dry out refractories?
Prevailing design technology for Dry-Cement Plants requires the installation of large volume of expensive refractory to cater for the high-temperature process. Newly installed refractories require a carefully controlled initial heating. If this initial heating is carried out too rapidly or erratically, then different rates of expansion between adjoining refractory areas may occur, creating stresses which cause severe cracking. Alternatively residual moisture may be converted to steam too quickly, resulting in explosive spalling.
Both these events will naturally impair the efficacy and life-expectancy of the refractory.
Most conventional process heat sources do not afford the close temperature control, particularly in the lower ranges (during which time steaming will normally take place) and so are less than ideally suited to carry out this initial dry-out or heat-up.
Further, temporary radiant heat sources, such as Flexible ceramic heating pads or blankets, will tend to "bake" the refractory surface, trapping moisture and driving it to the cold face and although the refractory hot face may appear adequately dried, the entrapped moisture will subsequently tend to create spalling when the plant is on stream.
It has become widely accepted in most Industries that the only truly effective means of drying out refractories is to deploy some form of convective heat source, passing large volumes of hot gases over the refractory surface.
This creates a "scrubbing" action on the object refractory, which hastens the heat-transfer process through the refractory thickness, ensuring that both residual and chemically- bonded moisture is rapidly and safely driven off.
(The Pratteln theory propounds that all surfaces comprise a series of layers which can be progressively disturbed by a "rubbing" or "scrubbing" action)
High velocity burners - the practical and effective solution
For over 30 years, the Hotwork-INTERNATIONAL has provided a refractory dry-out service to Industries worldwide, based on the use of its High Velocity gas or oil burner system. In the last decade, its deployment in the Cement Industry has become significantly more widespread.
This burner system is portable and highly flexible in terms of the required space for deployment. It is possible to position burners through virtually any reasonable-sized (150mm dia. +) orifice, so that the heat-input can be positioned in the most appropriate manner to provide uniform temperature distribution throughout the entire volume of the object plant.
The burners have a very high (some 100:1) turndown ratio, enabling temperatures to be accurately controlled at all stages from 80 to 1400 °C.
Each burner has an output which is fully adjustable up to 2.5 Million Kilocalories (10 million BTU) per hour, and is capable of passing some 5000 Nm³ per hour of hot gases when connected to its combustion air fan.
These hot gases are emitted at an outlet velocity of some 150 metres per second, which creates a turbulent atmosphere within the object plant, thus promoting the highly effective “scrubbing” action necessary to rapidly and safely drive off moisture.
The above-mentioned flexibility (in terms of physical deployment) renders the system ideal for the initial dry-out of the large and complex structures (notably the Dopol Tower) of the conventional modern Cement Plant. Heat input can be effected in all areas and levels of the plant, so that a uniformity of temperature is achieved in the initial dry-out process. Such temperature uniformity, as well as ensuring that the refractory is thoroughly dried-out before process heat is introduced, also minimizes mechanical stresses resulting from differing expansion rates in adjacent refractory areas, and helps to maximize plant campaign life.
In addition to the dry-out of Rotary Kilns, Kiln Sections, and Annular cooling pods after refractory repair, Hotwork-INTERNATIONAL has carried out initial heating and drying on various items of ancillary plant, such as:
- Dopol Towers
- Gasifier and associated Cyclone
- Kiln Ignition Hood
- Calciner
The following pages show sketches indicating burner and thermocouple deployment on two examples of such applications.
A typical heating cycle is shown below:
The extended holding periods at 200°C and 600°C assure a good “soak” of the refractories throughout the plant, eliminating the possibility of residual moisture subsequently causing cracking or explosive spalling.
Dry out of a cement plant gasifier, syphon and cyclone using the Hotwork-International high velocity burner system
Dry out of vement plant double-tower using the Hotwork-International high velocity burner system
The complete service
Hotwork-INTERNATIONAL is pleased to provide detailed offers and proposals, without obligation, for dry-out of refractories on receipt of relevant plant details.
On confirmation of order, it would be normal practise for a Hotwork-INTERNATIONAL engineer to visit site in advance of the scheduled start-date, to carry out an engineering visit, and to fully discuss all aspects of the operation with the relevant responsible plant personnel, in order that the respective responsibilities of the plant and Hotwork are clearly defined and understood, and that the plant is then able to carry out any necessray preparatory work to assure that the available “window” for the dry-out operation is not exceeded, and that unecessary delays before start-up are avoided.
Hotwork-INTERNATIONAL can provide burners suitable for operation on Propane, Natural Gas or light (diesel) oil. (Where oil is used as burner fuel, a compressed air supply is also necessary for oil atomizing purposes).
Typical burner assembling situation - GAS
Our burners have a max. capacity of 250 Nm3/h natural gas and max. 5000 Nm3/ combustion air.
Flames supervision by UV-cells. In case of flame failure, gas supply will be stopped within 2 s by safety shut-off electrovalve.
Pos.3: High-velocity-burner chambers for gas
| lenght | 2,4 m |
| form | cylindrical |
| max.diameter | 380 mm |
| cone diameter | 160 x 160 mm or 210 x 210 |
| weight | 55kg |
| connections to the burner | gas NW 50 ND 16 flange |
Pos.1: combustion air fan
| current consumption | 15 kW, directly starting |
| voltage | 220/380 V, 3 phases, neutral, earth, 63 A |
| dimensions | 800 x 1000 x 1320 (+ 800 x 1000 x 1850) (L x B x H), installed on wheels |
| weight | 460 kg |
| sound absorbing | 83 dba |
Typical burner assembling situation - OIL
Our burners have a max. capacity of 200 l light oil and max. 5000 Nm3/ combustion air.
Flames supervision by UV-cells. In case of flame failure, fuel supply will be stopped within 2 s by safety shut-off electrovalve.
Pos.3: High-velocity-burner chambers for oil
| lenght | 2,4 m |
| form | cylindrical |
| max.diameter | 380 mm |
| cone diameter | 160 x 160 mm or 210 x 210 |
| weight | 55kg |
| connections to the burner | light oil ½" quick action coupling compressed air ¾" quick action coupling |
Pos.1: combustion air fan
| current consumption | 15 kW, directly starting |
| voltage | 220/380 V, 3 phases, neutral, earth, 63 A |
| dimensions | 800 x 1000 x 1320 (+ 800 x 1000 x 1850) (L x B x H), installed on wheels |
| weight | 460 kg |
| sound absorbing | 83 db |
The only additional requirement (other than general plant preparation which would be defined in individual offers) would be the assistance with regards to movement of our equipment on site (e.g.fork lift truck/hoist/craneage).
The Hotwork-International High Velocity Burner system has been proven, over many thousands of diverse applications worlwide, to be an ideal method of drying-out new refractories in virtually any type of furnace, vessel or ductwork.
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