Operating Instructions for heat Exchangers

1. USE

Heat exchangers serve to transfer heat from one heat-carrying medium, flowing within the primary side of exchanger, to another hear-carrying medium (liquid) flowing through the secondary side of such exchanger. Parallel-flow and/or counter-flow connection are possible. In its counter-flow applications, the construction of MAX-type exchangers most closely approximate the theoretically ideal counter-flow heat exchanger concept. Given the steel of Class 17.248.4 used as major construction material, the exchanger meets the requirements of even most challenging applications such as those used for heating/cooling beverages or, alternatively, or those of aggressive liquids. Compared to the shell-side of the exchanger, the other side, i.e. the tube side, is characterized by an up to an 8-times higher hydraulic resistance. It then is this very hydraulic resistance that determines which side is used as the primary side, and which as the secondary. Whilst - customarily - tubes are on the primary side, the secondary side of the exchanger is in the shell. That largely applies to steam heaters. In terms of heat transfer, the sides are interchangeable.

2. INSTALLATION

Installation of exchangers needs to be carried out in a way preventing the transfer of forces and moments from installation onto their inlet sockets. That in practice means that fitting are mounted on the adjusted exchanger, and pipes are welded proceeding thereof. On the structure, the exchanger is fixed by no less than holders with sealings and bottom support. bottom support.

a) General guidelines:

Irrespective of the operational status of the heat exchanger, maximum temperature limits and maximum over-pressure volumes in both the tubes and the shell, as indicated in the heat exchanger passport and on the product tag supplied with the commodity, must not be exceeded. Appliances attached to the primary and secondary side of the heat exchanger shall be fitted compliant with respective ČSN standards, particularly with ČSN 06 0830 - Safety devices for central heating and SHW heating standard, containing binding provisions. Our recommendation is to install pollutant separation filters.

When the heat exchanger is in operation, jump increases/drops in pressure and temperature must not occur.

Requirements to be fixed when dealing with STEAM-WATER system:

Installation of the heat exchanger in vertical position to avoid water hammer;
installation of steam and condensate into heat exchanger´s pipes, not in shell;
continuous regulation of exchanger delivery on steam – use an emergency-function control valve.

Regulating exchanger output solely on condensate through flushing the heat-exchange surface with condensate can partly cause a loss of the control valve on condensate - at a low condensate flow taking place in, e.g., in a transition period, and partly bring the heated medium to a boil at the steam input in the exchanger - owing to low static pressure in the secondary system, or due to low throughput in the secondary system. As a result, the exchanger may suffer destruction.
Furthermore, the so-called action transport delay tends to occur at, e.g., a 70°C/90°C heat drop. In the central heating system, a circular pump outage occurs for some reason or another, all that at a time when the exchanger was producing top output, meaning that the heat-exchanger area thereof was not inundated at all. Though information on the turned-off condenser valve runs from the heat sensor mounted on the heating water supply to the regulator, and even with the valve being shut off, steam condensation proceeds, with the heat-exchange area being flooded, and steam continuing to enter the heat exchanger, thus further increasing the temperature of the feed heating water. It starts boiling, and the exchanger is likely to end up in destruction.

Using a counter-flow connection, the output provided by the heat exchanger exceeds that obtained from a parallel-flow connection.

b) Prior to putting a heat exchanger in operation, check whether

piping connections are compliant with the project
unwatering fittings are turned off.

c) Recommended procedure for putting WATER-WATER exchangers in operation

Fill the cold/secondary part of the system with power fluid, deaerate, and check working overpressure.
At a sedate pace, turn on the secondary-circuit shutting fittings, and turn on the circular pump.
Fill the hot/primary part of the system with power fluid, deaerate, and check working overpressure.
At a sedate pace, turn on primary-circuit shutting fittings, then slowly increase circulation in the hot part, and allow approx. 10 minutes for the exchanger to get preheated.
Shutting fittings shall be turned on at a sedate pace and by degrees so that a steady increase in temperatures, pressures and throughputs is achieved, thereby avoiding heat shocks and water hammers.
Turn on adjusting automatics and monitor parameters of respective circuits – temperature, pressure, and the proper operation of automatic control.

d) Recommended procedure for putting STEAM-WATER exchangers in operation

Fill the cold/secondary part of the system with power fluid, deaerate, and check working overpressure.
At a sedate pace, turn on the secondary-circuit shutting fittings, and turn on the circular pump.
Unwater the steam connection and let condensate out in order to avoid water hammers; check the steam working overpressure.
At a sedate pace, turn on the primary-circuit shutting fittings.
At a sedate pace, turn on shutting fittings at condensate traps in primary circuit, and allow approx. 10 minutes for the exchanger to preheat.
Shutting fittings shall be turned on at a sedate pace and by degrees so that a steady increase in temperatures, pressures and throughputs is achieved, thereby avoiding heat shocks and water hammers.
Turn on adjusting automatics and monitor parameters of respective circuits – temperature, pressure, and the proper operation of automatic control.

e) Recommended procedure for putting WATER-WATER (STEAM-WATER) exchangers on a standstill

At a sedate pace, close the primary medium.
Switch automatic control to manual control mode.
After exchanger´s cool down, turn on even secondary the secondary medium.
An exchanger supposed to be out of operation for a longer period of time, ought to be emptied and dried up using compressed air.
In danger of freezing, the exchanger must always be emptied.

f) WATER HARDNESS TREATMENT FACILITIES – recommended prescribed operation

In order to ensure both a reliable heat transfer and an appropriate life cycle of the heat exchanger installed in our systems, monitoring of water quality/composition is essential.

Upon heating DHW from a temperature of, e.g., 15°C to 55°C, a shift of the lime-carbonate balance in the direction of exclusion of indissoluble salts typically takes place whereby sediments are created. In that way, up to the temperature of 40°C, only calcium is excluded – in the form of calcium carbonate. At temperatures exceeding 40°C however even magnesium is excluded in the form of magnesium hydroxide and magnesium silicate. Again, this so-called boiler incrustation forms sediments.

From operational experience it follows that more than 30 % of exchanger failures are caused by poor water quality, by water hardness that is the cause of sediments and boiler scale occurrence. Both the requirements for the quality of water used in power facilities and the frequency of reviews conducted are hammered out in ČSN 07 7401, ČSN 07 0711, and ČSN 83 0616 standards.

Some of the most frequent types of water treatment plants are, e.g.,

Magnetic water treatment facility with the rectified magnetic field triggering - through resonance - a frequency swing of molecules; in consequence, the crystal structure gets broken.
Electrolytic water treatment plant, i.e. a facility equipped with an electrolyser located inside a pressure filter.

3. BOILING/BUMPING OF THE MEDIUM - warning

In case that the medium inside the heat exchanger comes to the boil, i.e. usually of the medium in the upper part of the exchanger where the temperatures of both the heating and heated medium are of top levels, this medium boil can be caused by e.g.

a delayed suspension of the heating medium flow (steam) into the exchanger; that may be due to an improperly designed control valve fitted on the condensate side of the exchanger, or due to improperly/slowly functioning emergency shut-off cock fitted on the steam side of the exchanger. These situations are likely to occur provided that the control valve on both the steam and condensate sides of the exchanger are designed improperly, meaning that either the valve fails to have authority, or was designed with an inadequate lift;
inadequate static pressure in the secondary system;
inadequate throughput in the secondary system.

4 . Recommended procedure for exchanger cleaning

In order to ensure proper functioning of the exchanger, water treatment is necessary, as is periodical chemical cleaning as a way of preventing the exchanger against clogging with scale.

Exchangers installed within a heating water system are recommended to undergo cleaning in periods of 36 months of operation time (pursuant to amount and quality of water replenished).
Exchangers used within the system of DHW production, appropriate water treatment is required – depending on throughput, hardness and composition of water within the region which the exchanger is run in.

Permeability and cleanness of a DHW exchanger´s areas can be checked using, e.g., an in-built differential manometer, and through measuring pressure loss on the secondary side. If and when such loss - at the exchanger´s full performance - exceeds by 30 % the value of pressure losses defined by the project in the exchanger design phase, or the value of pressure losses measured whilst running a new exchanger, the exchanger needs to be replaced.

Should the exchanger be choked with mechanical particles, it is advisable to flush it using operating medium, rinse it against the common workflow. However, in case that the exchanger is choked due to scale sediments, the situation is remedied by flushing the exchanger with a chemical acid & inhibitor. Wastewater needs to be defused and cooled down. Maximum temperature of wastewater discharged to the sewage network must not exceed 40°C.

As an example of an acid-based chemical removal of scale, flushing the exchanger with a 4% solution of nitric acid (HNO3), followed by a sweetening 0.1% solution of caustic lye (NaOH), may be given. Chemical cleaning is nonetheless an operation requiring professional chemical qualifications. It is therefore advisable to approach a professional firm.

The occurrence of sediments, incrustation, and of boiler lead to increasing pressure losses, aggravated heat transfer, and a subsequent drop in heat output. Those phenomena are not to be viewed as the exchanger defects, and cannot constitute the object of a quality claim. The manufacturer does not bear the cost of exchanger cleaning, nor is he liable for damages arising on the grounds thereof.

5. MARKING

Compliant with ČSN 06 0830 Standard, Art. 70, exchangers are tagged using durable index plates. Plates are located on the exchanger shell. Technical drawings of the exchanger constitute an integral part of the passport.

6. WRAPPING, STORAGE AND TRANSPORT

Exchangers do not require wrapping. They ought however to be stored at a shady place providing protection against atmospheric and corrosive effects. Pending transport and storage, necessary provisions must be made to avoid damage and contamination. What particularly needs to be borne in mind is the fact that, should there be water in the exchanger – both in the form of residue or rainwater - frost will certainly destroy the exchanger. The same applies even to the heating facilities put on a standstill in winter.