(recommendations how to winterize a concrete-mixing plant)
According to the statistics, only half of customers in our latitude buy concrete-mixing plants already winterized, which is a result of insufficient funds. Many of those who purchase summer versions of plants “upgrade” them to all-season later as the initial costs are being covered. And those who do not manage to “winterize” have to stand idle as a result of concrete-mixing plant being frozen. So what does an owner of a summer “breadwinner” have to know while getting ready to autumn-winter season?
First of all one has to determine, at what minimal ambient temperature it is worth producing concrete-mortar mixes. If we refer to southern regions of Russia or Ukraine it is reasonable to count upon not less than –5°С -8°С and to sacrifice 15-20 winter days with lower temperature. For other regions one has to decide either to sacrifice two-three cold months or to make considerable capital investments. But anyway in our opinion operation at temperatures below –15°С makes sense only when it is really necessary.
So, the main stages of winterizing the inner space of a concrete-mixing plant are:
1. Winterizing the inner space of concrete-mixing plants, winterizing the inclined gallery of a feeding conveyer or a skip hoist loader, winterizing (panelling) of aggregate bins.
Almost any company is able to winterize a concrete-mixing plant on its own. There is only a question which materials will be used for that and how accurate will it be carried out. Good if a summer version of a concrete-mixing plant has a framework allowing comparatively fast winterizing. But if there is no framework and its creation will be commissioned to people who might be irresponsible, the plant after winterizing may look like an ugly monster. Frameworks must be manufactured with due regard to drainage, must carry maximal winter and snow load specific for the region. Usually rolled steel is used to make frameworks: U-section №8÷10 on perimeter, bridging pieces and arcs – equal angle iron 63÷75 mm.
Choice of panelling (walling) material depends on a region where the concrete-mixing plant is installed and temperature, at which it is necessary to guarantee operation of the plant. In southern regions operation at near-zero temperatures may be ensured by means of panelling with profiled sheets of 0,8 – 1,2 mm thickness, which will protect expensive equipment from precipitation rather than from cold. But as for real winterizing of a concrete-mixing plant, it should be factory 3-layer winterizing sandwich-panels with foamed polyurethane or other filler of more than 50 mm thickness. Besides it is very preferable to have two types of panels (walling and roof), surely with cover strips and other leakproof materials. In general it would be a perfect choice to entrust such work to a specializing expert company.
2. Aggregates heating, service water heating, concrete-mixing plant internal space heating, operator’s cabin heating
Sellers of concrete-mixing equipment often do not install all the necessary equipment for cold weather operation even on winter variant of the equipment. A buyer purchasing equipment does not know himself at what temperatures will his concrete-mixing plant operate, what kind of fuel will be used for heating, which method of aggregates heating is the most progressive and efficient as well as other aspects of this issue. Answers usually come later as the concrete-mixing plant operates, local market of heating agents and other companies’ experience are being studied.
The most energy-consuming process is aggregates heating. Aggregate bins should be (except for panelling with an insulation) correspondingly improved: additionally equipped with winterized cover having an open-close mechanism; depending on heating method the tubular revolving register air grids or injectors for jet steam or a special diffuser system for hot air injection are installed in the inner space of a concrete-mixing plant. Choice of reasonable heating method and corresponding selection of necessary heating equipment – up to concrete-mixing plant’s owner.
The most widespread and conservative system – feeding hot water from ordinary boiler to tubular revolving register air grids via circular system (ø108 – ø159mm), built into aggregate bins. Via a water heater-heat exchanger this very boiler could heat service water to be added to the concrete mix, and by means of ordinary cast iron radiators heat the inner space of a concrete-mixing plant. Advantages – comparatively cheap boiler and pipe equipment, which does not demand the staff to have special skills; wide variety of boilers working on gas, liquid or solid fuel; if there is a heating line nearby – possibility to get heat conductor from central boiler house. Disadvantage – low system efficiency and therefore long initial heating up of materials in a bin (e.g. after a night). Experience of companies using such a system has shown that in order to heat aggregates, water and concrete-mixing plant SB-145-4 premises at -10÷15°С one needs 500÷600Mcal/h of thermal power. For reference – SB-145-4 concrete-mixing plant (manufactured by Betonmash company, Slavyansk, Donetsk region) has performance of up to 40m³/h, aggregate bins 120 t (4 compartments), service water tank 2000l, winterizing – sandwich-panels of 50 mm thickness.
A more modern unfreezing (heating) system – direct injection of jet steam into aggregates through special injectors. This technology is successfully implemented by Interblock engineering company (Russia, interblock.ru) which uses Canadian ST series snap-action steam generators. According to company’s information the technology is highly efficient, provides 110-160°С steam supply in 15 seconds after starting the steam generator. Moreover such technology demands no installation of smoke flue (end products of fuel combustion are not emitted into atmosphere) and complex water treatment systems. Drawbacks: aggregates are saturated with condensed water vapor which needs to be drained from under the silos, besides there are oil remainders of combustion products in aggregates as the steam generator works on liquid fuel.
The most innovative and progressive method – warming aggregates up with hot air using SIMUN generators and heating water with GEYSER boilers manufactured by IONE S.r.l or analog BOOSTER equipment by Sauter company (Switzerland, sauterag.com). Hot air 200 - 260°С under 0,2 – 0,4 bar pressure is fed through perforated diffusers to the lower part of aggregate bins, heating them efficiently. At the beginning of heating process injection of water into hot air is allowed to increase heat emission and speed up unfreezing. The fuel combustion gases do not get into hot airstream, in a heat exchanger they give up their heat for heating water, cool down to 40-60°С and are removed beyond circuit via a low-temperature tube. Advantages of such system – aggregates are being heated and dried at the same time, high efficiency, eco-friendly technology. Disadvantage – expensive equipment - heating equipment for a concrete-mixing plant with performance 40-60m³/h costs about 90000 EUR, The price may make 110000 EUR if it includes installation of a generator, boiler and fuel reservoirs in a special container.
Certainly the best way of choosing the heating method would be to visit the company using it, preferably not in the first year. Only in such way you could get objective information from original source. In this case you would get objective information about advantages and disadvantages of each method, maybe even learn some new ones, which were not mentioned above.