In Ukraine, most of the CHP / TPPs, due to the existing schedule, require conservation of the main equipment. At the same time, it is important that the method of equipment preservation is not only reliable, but also low-cost. Today, the most common methods require the use of expensive and, not least, environmentally hazardous chemical methods in which work surfaces are treated with octadecylamine. It is worth saying that in world practice this option for protecting equipment has not found wide application.
In addition, there is another way — to transfer phosphate water chemistry regimes, which are traditional, to the use of foreign reagents (such as Helamin and Epuramin), famous for their preservative properties. This option is also not cheap.
For example: mothballing a 300-megawatt power unit with octadecylamine costs at least 100,000 hryvnias, and the cost of disposing of the spent composition, as a rule, is not indicated.
As for the work of the Ukrainian thermal power industry, it has a number of specific features: limited funding, heavily worn out equipment, peak operation, etc.
Based on this, a number of rules for the conservation of equipment of Ukrainian CHPPs, TPPs are distinguished:
the presence of a sufficient long period of use;
financial accessibility and expediency;
compliance with current regulatory documents;
reliability, efficiency in fulfilling the assigned tasks;
meeting the requirements for environmental safety;
maximum uniformity for all types of equipment.
The rate of development of parking corrosion on the surfaces of equipment primarily depends on the degree of moisture content of the corroding metal. For example, for boiler steel, which is in an atmosphere of clean air, the maximum relative humidity parameter is 60%. If this value exceeds 60%, the rate of development of atmospheric corrosion increases sharply.
*** According to studies, at an increased humidity level (from 60% to 100%), corrosion processes proceed 100-2 thousand times faster than under “dry” conditions corresponding to the norm (for example, with an air humidity of 30-40 %).
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Why carry out the conservation of equipment of CHP, TPP?
Let us prove the need for conserving the equipment using an example. The weight rate of parking corrosion of boiler house steel is on average 0.05 g/(m2 h). This is subject to the free supply of oxygen and relative humidity within 60%. The norm for power equipment is 0.03 g / (m2 h), which indicates a decrease in wall thickness of approximately 0.057 mm per year.
Thanks to reliable conservation of TPP / CHP equipment:
the safety of power equipment is ensured;
reduce the cost of restoration and repair of units;
technical and economic parameters of stations are supported;
In addition, the costs of production processes are reduced.
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Basic methods of conservation of equipment of thermal power plants, thermal power plants
Methods of conservation of equipment are determined by the relevant package of regulatory papers.
Based on the distinctive features of the thermal scheme, as well as the duration of stay in reserve, the safety of equipment can be carried out by the following methods:
heated air currents or dried air;
by filling with deaerated water while maintaining excess pressure;
corrosion inhibitors, nitrogen or hydrazine-ammonia agent;
ammonia composition or gaseous from cylinders;
contact inhibitors MSDA, M-1, etc.;
ammonia means Trilon B;
inhibited air currents;
From the point of view of environmental feasibility, reliability and efficiency, of all the above proposed options, the most preferable method is the conservation of CHP / TPP equipment with dried air.
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Rotary dryer for equipment conservation: how, why and why
Preservation of equipment with dry air involves the complete extraction of moisture from the object with a decrease in humidity to a level of 40%. With such an indicator, the parking corrosion rate, remaining constant throughout the circuit, decreases to the required 0.03 g/(m2 h).
In order to avoid the appearance of “dead zones” in the conserved object, special attention should be paid to the choice of dehumidifier equipment, among which rotary air dryers are advised to give preference.
How does a rotary air dryer work?
The rotary type technique has excellent adsorbing characteristics. In these devices, the design of the rotor surface resembles a honeycomb. This design solution promotes laminar air flow (dry and regenerative), which reduces friction losses.
Air is supplied to the dryer rotor surface in such a way that the dried air flows pass through 85% of the rotor surface, and regeneration air passes through the remaining 15%, which is preheated to the desired temperature. At the same time, the excess pressure of water vapor contributes to the effective exchange of moisture between the sorbent and air, and the quality control of regeneration is carried out by the temperature of the regeneration air flows. Moreover, the regeneration air cleans the rotor from dirt and dust that enters the dryer with the working air.
By adjusting the temperature of the regeneration flows, the ability to maintain the relative humidity of the working air at a given level becomes quite real. And thanks to the rotation of the rotor, the process of sorption of the working air flows is combined with the regeneration of the sorbent (at the same time, the overflows of air flows are minimized due to the presence of compaction of the sectors). You can use the installation without reference to the sewerage system, because. condensation is completely absent.
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Features of Rotary Air Dryers
Rotary type equipment is equipped with a complex system for adjusting the humidity level with a capacity setting sensor and a control unit. The instrument display shows the actual relative humidity as a percentage. Moreover, the control unit can be preset for alarm/control parameters as well as for maintaining the desired relative humidity level.
Rotary dryers comply with the following European standards:
standard EN 50082 (part No. 2) — industrial environment, electromagnetic compatibility standards, general immunity standards;
standard EN 746 (part No. 2) — requirements for the safety of the system for the processing of fuel and gaseous food products;
standard EN 50081 (part No. 1) — standards for electromagnetic compatibility, as well as emission requirements;
standard EN 60204 — general requirements for the safety of machines and electrical equipment.
*** Based on the performance of the rotary dryer (from 240 to 7.6 thousand m3/h), the unit consumes 1.51-82 kW of electricity.
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Features of dry preservation of equipment: boilers, turbine units, compressor
In the thermal power industry, rotary air dryers are used for the conservation of boilers, including a superheater, radiant heating surfaces, an economizer, electrostatic precipitators, flow components of turbines, a gas section, a generator, etc.
Due to the connection of a regular compressor of a rotary air dryer to the suction, the reliability of the operation of air circuit breakers is increased, the appearance of an oxide film on current-carrying parts is prevented.
For the conservation of equipment with dried air, the most reliable method is the closed circuit principle. In this case, all component devices are combined into a vicious circle by means of temporary pipelines and standard fittings, and are purged using an air-drying device included in the circuit.
Thus, the rotary dryer extracts moisture from the conserved circuit, the volume of which coincides with the number of non-drained zones of the boiler heating surfaces.
When choosing a rotary dryer for this method of conservation of TPP equipment, CHP should pay attention to the performance of the device in terms of dry air, taking into account aerodynamic resistance, the volume of the preserved circuit, and the estimated mass of condensate to be removed.
*** After the conservation is completed, the equipment is hermetically sealed and put into reserve. But through leaks in the fittings, moisture can seep into the circuit from the outside, so it is recommended to perform periodic purges.
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The installation of a rotary dryer before the compressor makes it possible to supply pre-prepared air with a dew point of -40 ° C to the suction. This increases the efficiency and reduces the load on the condensate drain, due to a significant decrease in the volume of drip moisture.
In addition, the use of a rotary dryer when the compressor is placed on standby ensures that the condensate drainage system, air supply lines, and working surfaces are blown with dry air. This will protect the preserved objects from damage by parking corrosion during their downtime.
Conservation of turbo-units
For conservation of turbine units, the most attractive method is the open circuit method, where the dried air is continuously supplied through revisions, drains and purge fittings, and the exhaust is produced through the fittings on the suction manifold. The complete removal of moisture from the steam space of the condenser and the flow element of the turbine is evidenced by the equal value of the relative humidity of the air at the inlet and outlet of the circuit.
To increase the efficiency of this process, an air ejector is installed to force the removal of air flows from the circuit. The hourly flow rate of dehumidified air flows required to extract moisture is approximately 10% of the circuit volume. Just as in the case of boilers, it is recommended to periodically purge the flow path of the turbine.
*** To control the quality of equipment conservation, a special sensor is installed at the outlet of the circuit.
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How is the quality control of equipment conservation with dry air carried out?
To control the quality of conservation of TPP / CHP equipment by means of dry air, a special corrosion indicator is installed in the preserved circuit. Experimental samples of corrosion formations are marked with a number, after which they are weighed and stored in a dry environment, in a desiccator until they are placed at the test point.
Before installing a prototype, it is placed in a cassette, which consists of a threaded copper rod (Ø 8 mm). On this rod, separated from each other by Teflon bushings, three samples are put on and compressed on both sides with screwed nuts. Then the cassette is placed in the controlled object in such a way that it does not come into contact with the details of the installation and metal.
Next, the corrosion processes occurring on the surface of the samples are evaluated. It is recommended to produce:
quality method. It involves an external examination of the prototype, which occurs after its removal from the object. Here the presence of traces of corrosion is established.
in a quantitative way. Carried out in laboratory conditions to determine the weight loss (required accuracy ± 0.1 mg), which will determine the rate of corrosion processes.
After the control, before weighing, corrosion products are removed from the prototypes using one of the methods: electrochemical, mechanical, chemical.
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Benefits of using a rotary dryer in the conservation of TPP / CHP equipment
In the global energy industry, the efficiency and reliability of equipment conservation with dry air has been confirmed at more than 500 facilities. And that’s just in Europe. Rotary dehumidifiers are actively used by leading energy companies from the Czech Republic, Germany, Great Britain, Poland, Finland, Austria, Italy, Denmark, etc., while maintaining their equipment.
Dry air, as the main or only method of conservation, protects the following equipment from corrosion damage: generator; turbine; gas / steam-water path, boiler; capacitor; electrostatic precipitators; ash removal system; superheater; transformer; equipment of onshore pumping stations; block pumping equipment, etc.
For example, currently 202 turbine units in Germany are equipped with a dry preservation system based on a rotary dryer.
So, to summarize: conservation of TPP / CHP equipment by dry method using a rotary dryer:
Guarantees reliable protection of conserved objects during the entire downtime period (up to 12 months).
Allows you to continuously purge the circuit due to the relatively low power consumption of devices for drying air flows.
Allows you to automate the procedure for maintaining the required conditions during the conservation of turbines by installing a special humidity control sensor at the outlet of the condenser, as well as at the bottom of the boiler unit.
Requires a one-time investment for the purchase of a rotary dryer, which on average lasts up to 10 years (without the need to replace the sorption rotor). The annual expenditure on the use of air-drying devices is no more than 3% of the purchase cost of the units.
It is absolutely environmentally friendly and applicable to any type of installation.
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If you have any questions about the use of rotary dryers for the conservation of TPP / CHP equipment, please contact the managers of the Pobut online store by phone: (097) 586 81 58.