Introduction
The subject of sewage sludge has become one of the main operational and management problems of sewage treatment plants in recent years, as the restriction on spreading in agriculture has increased disposal costs. If dewatering can be defined as a consolidated technology, which has recently seen the advent on the market of both screw presses and advanced centrifuges, for drying the technological development is still ongoing and we position ourselves on the market as a valuable technical partner for the realisation of even the most complex systems.
BELT DRYING
Low-temperature belt drying essentially exploits heat transmission by convection rather than radiation. Compared to a rotary drum, higher retention times are maintained by reducing speed and operating temperature. The machine itself is more complex but allows any residual heat energy from the plant to be used (typically water at around 80°C) and from an authorisation point of view, the procedure is simpler (there is no combustion chamber for heat production). The material to be dried is evenly distributed and then moved on special air-permeable conveyor belts. From a constructional point of view, the construction takes place in modules developed in length.
ROTARY DRUM DRYING
Rotary drying is one of the main drying methods existing in unitary chemical engineering operations. Drying takes place in rotary dryers, which consist of a cylindrical shell rotated on bearings, if necessary slightly inclined to the horizontal. The feed of wet material occurs at the upper end of the dryer and proceeds through it by virtue of the rotation, the flow-breaking effect and the possible inclination of the shell, delivering the dried product to the other end. The direction of gas flow through the cylinder with respect to solids is mainly dictated by the properties of the material being processed. Co-current flow is used for heat-sensitive materials, even for high inlet gas temperatures, due to the rapid cooling of the gas during the initial evaporation of surface moisture, while for other materials, countercurrent flow is appropriate to take advantage of the higher thermal efficiency that can be achieved in this way. In the first case, the gas flow increases the solid flow rate, while in the second case, it reduces it. The preferred method of heat transfer is the direct method (direct exchange between gas and solids). The direct dryer consists of a metal cylinder lined on the inside with insulating refractories, making it suitable for operation at high temperatures. The accessory components of the direct heated rotary dryer include a combustion chamber for operation at high temperatures. The gases are forced through the cylinder by an aspirator (especially when a low pressure drop heater is used) or by a combination of aspirator-blower, which is suitable for maintaining precise control of the internal pressure even when there is a high pressure drop in the system. The characteristics of the material to be dried determine the feeding method, normally a screw conveyor. The feed is controlled and uniform in terms of quality and quantity. The advantage of the rotary drum is its simple construction, high efficiency, low routine maintenance costs and durability.
MUD.
FIDIA ENGINEERING S.r.l.
Sede legale: Via Enrico Fermi 32 – 24020 Scanzorosciate (BG)
Sede operativa, magazzino e officina: Via A. Moro 1 – 24020 Scanzorosciate (BG)
Cap. Soc. € 500.000,00 i.v.
R.I. BG, Cod. Fisc. e P.I. 02887960165
Cod. Univoco SUBM70N
REA 331280