Description of the process
The BIODESTIL process designed for the treatment of highly contaminated waste has the following sections:
INFLUENT SECTION
Odcieki są dostarczane systemem rurowym do zbiornika wejściowego. Zbiornik ten jest wyposażony w układ pomiarowy pH. W tym miejscu do wody ściekowej są dodawane odpowiednie związki reaktywne, dozowane według ilości i rodzajów ścieków w celu optymalizacji wydajności procesu parowania. Dodatki są dozowane automatycznie. Jeżeli ścieki tego wymagają, przed doprowadzeniem do parownika mogą być przepuszczane przez sito.
Depending on the treated waste requirements, the correct dose of reagents for the optimisation of the performance and operation of the evaporation process are applied in the influent section. These doses are applied automatically. Furthermore, and depending upon the nature of the influent, a sieving phase can be introduced prior to the feed to the evaporator.
THERMAL SECTION
The thermal section generates the heating fluid (hot water) required to bring the wastewater to boiling point.
The heating fluid is obtained from the combustion gases generated in a boiler as a result of the combustion of fuel. The fuels used may be varied, and are generally solids, making use of any type of biomass such as almond shells, saw-dust, forest or urban pruning and wood chips. However, conventional fuels such as granulated carbon, diesel fuel or natural gas may also be used.
Furthermore, any excess heat source with a thermal level higher than 80ºC may be used, by adding the necessary optional equipment to this offer. This allows the operational costs of thermal energy to be reduced in proportion to the heat contributed.
Combustion gases are emitted through a chimney stack after treatment with a cyclone, where the nature of the fuel used so requires, in order to reduce particle emission.
The boiler operation is controlled by a thermostat. The thermostat enables fuel to be supplied below the minimum temperature and cuts off the fuel supply when the maximum operating temperature is reached. In addition, the boiler is fitted with a safety thermostat which switches off the boiler if the temperature of the heating fluid increases beyond control.
The boiler enables combustion by primary and secondary air at the same time as a furnace covered in refractory brick. This solution allows greater energy efficiency than conventional boilers. It also obtains better emission values and is more durable. Moreover, the boilers do not require any type of civil work thus avoiding imbalances in the design which affect the later functioning of the boiler.
The heating fluid is constantly re-circulated from the boiler to the evaporator in a closed circuit. The fluid is re-circulated using a centrifugal pump especially designed for working with hot fluids. The heating fluid closed circuit is protected from overpressures by an expansion tank, which is also used to fill the circuit.
EVAPORATION AND CONDENSATION SECTION
This section is the true success story of the Biodestil process. Correct evaporation is able to considerably reduce the contamination parameters independently of the initial contamination load, while the toxic substances in the waste affecting its biological treatment are destroyed. This section has a series of pieces of equipment:
Liquid-vapour separator
The liquid-vapour separator is the evaporation unit where the wastewater boils and separates in two stages, vapour which reaches the condenser, and liquid which accumulates at the base of the evaporator. The liquid-vapour separator is a cylindrical body with an upper and lower cap made of suitable material. The entire separator is insulated to reduce heat losses, thus reducing the operating costs of the plant.
The liquid-vapour separator incorporates the heat exchanger and the level controller. The non-evaporable waste collects at the bottom of the separator, and is then extracted manually by opening a valve when the density reaches a certain value.
Heat exchanger
The heat exchanger is especially designed to ensure the correct boiling of the waste. If the evaporation parameters (speed, temperature, pressure) are not designed correctly, the distillate will be contaminated, due to the variable behaviour of the waste under these parameters. The design of the Biodestil heat exchanger is based on broad experience, giving this equipment a high degree of reliability in terms of both functionality and durability
Level controller
This equipment ensures that the wastewater level inside the evaporator is suitable for the correct boiling of the waste. The level controller automatically closes the feeder pipe to the evaporator when the level inside rises above a pre-determined optimum level. Furthermore, it allows the feed to pass provided that the level is below this value.
Condenser
The condenser removes the necessary calories from the vapour which has been generated to provoke total condensation. This equipment, as with the heat exchanger, has been designed on the basis of long experience, thus guaranteeing that it will operate correctly and be long-lasting.
The coolant used in the condenser is water. The water used for cooling is taken from the fully treated water which means that there is a self-supplying system within the Biodestil process, thus avoiding almost any consumption of coolant water and producing almost zero waste.
Vacuum pump and condensed water extraction pump
The evaporation operation is carried out at below atmospheric pressure. This allows the waste to reach boiling point at a temperature below 100ºC. In this way, the evaporation energy requirements are reduced, and therefore fuel requirements are lower than for evaporation at atmospheric pressure. The vacuum generated is produced using a liquid ring vacuum pump. The condensed water generated in the condenser is extracted using a suitable centrifugal pump.
COOLANT SECTION
The coolant section uses a liquid coolant (water) to condense the vapour generated in the evaporator in the condenser. The coolant is driven, in a closed circuit, from the accumulation tank in the cooling tower to the condenser.
In the cooling tower, the water to be cooled falls in a current of air generated by power fans. A large part of the water evaporates and is transferred to the air in the form of vapour. The energy required for evaporation is obtained by reducing the temperature of the water which reaches the bottom of the tower without evaporating. This cold water at the bottom of the tower is then used as coolant in the condenser.
The cooling tower loses water through evaporation. These losses are replaced using the final treated water or water from the mains.
STRIPPING - SCRUBBER SECTION
This process is used on those occasions when the final ammonium nitrogen content of the leachate to be treated exceeds the limits established for disposal.
This section has two parts: stripping and scrubber.
In the stripping section the condensed water from the evaporation and condensation section is pumped to the upper part of the stripping and falls against the flow by means of an air stream through a filling. In this process, the ammonia and other contaminating volatile substances present in the condensed water are transferred to the air stream and are thus removed from the water. To help the desorption process, a basic reagent may be added to the waste prior to reaching the stripping process.
In the scrubber, the opposite takes place: here, the ammonia and other volatile substances desorbed in the previous stripping process are fixed into a stream of re-circulating water. An acid reagent is added to the stream of water to fix the ammonia in the water and thus concentrate it. The scrubber air output is used as the stripping fan intake, and therefore the process is closed, thus preventing emissions and smells.
BIOLOGICAL SECTION
The steam condensed in the condenser lacks substances that are not easily biodegradable since only substances which are more volatile than water were able to evaporate, and these substances are of a simple composition. The condensed steam is fed into the biological reactor through a centrifugal pump. This biological reactor allows adequate contamination output levels for public watercourses.
The pH value of the biological reactor is altered in order to adequately adjust the pH values of the distillate to feed it into the reactor.
The process which takes place in the aerobic reactor is a complete mixture process, all points in the reactor have the same properties, in terms of microorganisms and air. The biological oxidation produced consists in the assimilation of organic material present in the distillation, in the presence of oxygen and nutrients.
The main reactions of aerobic treatment are:
- Synthesis reaction: this involves the assimilation or incorporation of nutritive elements into the cytoplasm of the microorganisms, thus producing new molecules. In this reaction, part of the organic material is used as an energy source and the rest to create new organisms.
- Oxidation or endogenous respiration reaction: this consists of the autoxidation of the cellular cytoplasm by the microorganisms and is produced when there is a lack of organic material used as food. When this occurs, nutritional elements used in synthesis are released. A fraction of the cytoplasm is transformed into water and carbon dioxide, so that the microorganism mass is reduced.
The biological reactor is designed so that the water retention time is adequate to ensure the total biodegradation of the waste. The oxygen will be transferred through a system which is adapted to the oxygen and reactor dimension needs.
To recirculate and drain the sludge a decanter with a central settling tank for feeding and Thompson profile of the treated water output is used.