Theoretical Informations

Intermittent (Bottom) Blowdown

Suspended solids in the boiler can be suspended as long as the boiler water is active (turbulent), but as soon as the agitation stops, it sinks to the bottom of the boiler. If the solids that settle to the bottom are not removed from the boiler, it will prevent heat transfer from the boiler flame-smoke pipes within a certain period of time and this may cause overheating and even deterioration (collapse) in the boiler construction.

The recommended method for removing this sludge is to blowdown from the bottom of the boiler by means of a blowdown valve. The purpose of doing it intermittently is to allow time for the sludge to redistribute itself so that more can be removed at the next blowdown. This is why a single four-second blowdown every eight hours is much more effective than a long blowdown every twelve hours.

With Vira BK 4000 Bottom Blowdown Controller, you can set the desired bottom blowdown time and how long you want to do. In addition, if the BKV 4000 Bottom Blowdown valve remains open or does not open for any reason, you can receive its information and intervene. Also, you can continuously monitor information such as the remaining time to the next blowdown and the set time via the controller.

The blowdown water is released into either a brick lined drain pit placed underground or a steel blowdown vessel above ground. The size of the blowdown tank is determined by the flow rate of the blowdown water and flash steam entering the vessel when the blowdown valve is opened.

Intermittent (Bottom) Blowdown Suspended solids in the boiler can be suspended as long as the boiler water is active (turbulent), but as soon as the agitation stops, it sinks to the bottom of the boiler. If the solids that settle to the bottom are not removed from the boiler, it will prevent heat transfer from the boiler flame-smoke pipes within a certain period of time and this may cause overheating and even deterioration (collapse) in the boiler construction. The recommended method for removing this sludge is to blowdown from the bottom of the boiler by means of a blowdown valve. The purpose of doing it intermittently is to allow time for the sludge to redistribute itself so that more can be removed at the next blowdown. This is why a single four-second blowdown every eight hours is much more effective than a long blowdown every twelve hours. With Vira BK 4000 Bottom Blowdown Controller, you can set the desired bottom blowdown time and how long you want to do. In addition, if the BKV 4000 Bottom Blowdown valve remains open or does not open for any reason, you can receive its information and intervene. Also, you can continuously monitor information such as the remaining time to the next blowdown and the set time via the controller. The blowdown water is released into either a brick lined drain pit placed underground or a steel blowdown vessel above ground. The size of the blowdown tank is determined by the flow rate of the blowdown water and flash steam entering the vessel when the blowdown valve is opened. Although the use of a blowdown tank is not compulsory in Turkey, there are regulations in many countries of the world regarding the temperature of the drained water as it may harm the environment and human health, and the use of a blowdown tank becomes mandatory due to these regulations. For example, in England, it is desirable that the drained blowdown water should not be above 43 °C and the blowdown ratio should not be more than 5% of the boiler capacity. When these conditions are met, most of the time the water in the blowdown tank is naturally cooled and drained through heat transfer and heat dissipation. However, if the boiler design and system conditions do not comply with these regulations, an extra cooling system may be needed in the blowdown tank.

The main effects on the blowdown rate are:

• Boiler Pressure
• Blowdown Line Size
• Length of the blowdown line between the boiler and the blowdown tank

In practice, a reasonable blowdown line length is 7.5 m and often sizing is done accordingly. The blowdown lines will include elbows, check valves, and the blowdown valve itself, and these parts will cause a pressure drop along the blowdown line. From the tables, the equivalent pipe length can be calculated according to the diameters of these elbows, valves, check valves, etc., and can be added to the total pipe length.

Level Control Systems

Boiler drum level control systems are widely used in industrial boilers to control the level of boiling water in boiler drums and to help ensure a continuous supply of steam.

If the level is too high, water can be carried over to the steam line, resulting in low dryness percentage of steam.

A level control system tightly controls the level in the event of an increase or decrease in steam demand regardless of the feedwater flow variation.

A tight water level control in the drum of a boiler can be achieved by using one of these systems.

• Single Element Level Control System
• Two Element Level Control System
• Three Element Level Control System

Maintaining the correct water level in the drum is critical for many reasons. Too high water level means transport of water and impurities to the steam line and poor quality steam production. In addition, possible water hammer hits and damage to equipment can be very costly.

Too low water level will cause boiler deformation and even collapse due to overheating in the fire tubes. Normally, the water level in the drum is expected to be kept within 2 to 5 cm of the normal water level point and with some tolerance for temporary load changes.

Factors Effecting Drum Level

In boiling conditions, steam bubbles are located below the water surface and have a volume. This situation may increase the water level in the boiler and cause an incorrect level information to be received. Another effect on the water level in the drum is the pressure.

The bubbles expand or shrink as the load demand changes. A higher steam demand will cause the pressure of the water in the drum to drop and the steam bubbles to expand to give the appearance of a higher water level than they actually are.

This imaginary high water level causes the feedwater to be closed at a time when more water is needed. The increase in water level as a result of the drop in drum pressure is called "swell". The decrease in the water level caused by the increase in drum pressure is called "shrink".

Drum Level Control Strategies

The single element level control system is a useful method for constant load conditions. However, it cannot respond quickly enough when load changes are more frequent, unpredictable, or severe.

More information should be input and processed to predict the amount of water to be added to the drum to compensate for sudden load changes. The addition of some information providing elements to the system (such as flow meter and transmitter) allows the controller to estimate the amount of water added to keep the drum water level within a specified range.

Single Element Level Control

This is a very simple drum water level control system. It requires a single analog input to operate and provides a single analog output in return. This is why it is called a single element drum level control. Because there is no relationship between the drum water level and the steam or feedwater flow, it can only be applied with a single feed pump in a single boiler providing a relatively stable load.

Its performance is ineffective compared to two element and three element level control systems. Example usage method is shown in the image below.

This system consists of a proportional signal coming from a level transmitter. This signal is compared with a previously set point and the difference found as the deviation value. This signal is passed to the feed water valve by the controller as a proportional output. Thus, the flow level of the feed water is adjusted by the valve.

Notes:

• Only one analog input and one analog output are required.
• Since there is no relationship between the drum level and the steam or feed water flow, it can only be used in single boiler - single feed pump structures with stable loads.
• It will be insufficient in places where swelling may occur.

Two Element Level Control

This drum level control design is suitable for single drum boilers with constant pressure of the feed water.

The two element drum water level control system includes the same level element and feed valve used in the single element configuration, but has an additional steam flow meter element providing a density corrected (by the controller) mass flow signal to control feedwater flow,

The two-element drum water level control system can be applied to a single drum boiler where the feed water is at a constant pressure.

The presence of double control elements in such a system is to provide a constant drum level control.

Example usage method is shown in the image below.

Notes:

• More accurate control of drum water level than a single element
• Steam flow acts as a forward feed signal to allow faster level adjustments.
• Can be applied to single boiler / single feed pump configurations with constant feedwater pressure.

Three Element Level Control

The three element drum water level control is suitable for the use of variable feedwater pressure or multiple boilers with multiple feedwater pumps.

In this design, three elements are used to control the level, steam and feedwater flow, respectively. This system offers much better and improved drum water level control than any other system.

For the best control, the correct flow values of both steam and feed water in terms of density must be maintained.

Example usage method is shown in the image below.

The 3 Elements Drum level control system is suitable to be used when there are more than one boiler and more than one pump or when the feed water is not constant in terms of pressure and steam consumption.

3 Elements Level Control System Components :

• Level Element
• Steam Flow Meter
• Water Flow Meter and Feedwater Valve

The level element and steam flow meter correct the errors that cannot be measured in the system due to blowdown or leakage from the boiler pipes.

The feed water flow meter, together with the feedwater valve, responds quickly to changes in feed water demand.

In order to achieve optimum control, steam and feed water flow values should be corrected with density.

Notes:

• The 3 Element drum level control system is an effective and accurate method for fluctuating steam loads.
• Ideal where a system suffers from fluctuating feedwater pressure and flow rate.
• A more advanced level of control is required.

Blowdown, is the process of removing some of the boiler water from the boiler drum in order to reduce the amount of dissolved or suspended solids.

The concentration of solid particles entering the boiler together with the feed water, increases considerably with the evaporation of the boiler water.

Solid particles dissolved and suspended in the boiler water are important for the control of the boiler water quality. The TDS level should remain within the limits specified by the boiler manufacturer and applicable guidelines. For this purpose, a certain amount of boiler water is discharged continuously (surface blowdown) and periodically (bottom blowdown).

High amount of dissolved solids (TDS) can cause many problems such as water carryover and scale formation:

Scale

The scale is mainly caused by the presence of calcium and magnesium salts (carbonates or sulphates), which are soluble in heat, or a very high concentration of silica relative to the alkalinity of the water in the boiler.

The scale layer is caused by the precipitation of impurities coming from the feed water directly in the boiler on the heat transfer surfaces, or from the substance suspended in the water, which settles on the metal and becomes hard and sticky. Evaporation in a boiler causes an increase in the concentration of impurities. This prevents heat transfers and leads to overheating in the boiler pipes. The less heat they transmit on these surfaces, the more hazardous there is.

Blowdown cannot eliminate the problem of formation of scale layer alone, but it can keep the boiler water conductivity and quality at the desired level. It helps to prevent the formation of the scale layer by chemical dosing of the feed water.

No mechanical treatment should be performed on the scale formed surfaces. Chemical flushing should be done.

Water Carryover

The high concentration of dissolved and suspended solid particles not only prevents heat transfer, but also causes the boiler water to foam. This can lead to the transport of solid particles and water along with the steam to the pipeline. Water Carryover causes both the quality of the steam to decrease and can cause great damage to the fixtures in the installation.

Automatic Surface Blowdown (TDS Control) System

Automatic Surface Blowdown Control system measures the conductivity in the boiler water with the conductivity probe and compares it with the maximum conductivity value set on the controller and tries to keep the conductivity of the water in the boiler constant by opening and closing the continuous blowdown valve. This is the most efficient system for surface blowdown in steam boilers.

If the conductivity (µS / cm) value is above the maximum allowable (set) conductivity value, the boiler water is blowdown until the conductivity value falls below the set value. If the boiler water conductivity value is below the set value, the blowdown valve maintains its closed position.

Automatic Bottom Blowdown System

Oil, rust, dirt and salts that do not dissolve in water, which may come from the installation, settle to the bottom of the boiler and form sludge. The automatic bottom blowdown system is used to discharge this sludge that accumulates at the bottom of the boiler. The bottom sludge will prevent heat transfer in the boiler and cause inefficient operation. This can cause mechanical collapse and even explosions. The recommended bottom blowdown time is 3-5 seconds every 8 hours.

At the set time and time interval in the controller, the bottom blowdown valve opens and the sludge settled at the bottom of the boiler clears. The feature that distinguishes Vira BK 4000 controller from ordinary timers is that it can be received an alarm if the valve remains open or closed.

Not: BS4-T Automatic Surface Blowdown System and DB2 Automatic Bottom Blowdown System are suitable for working in steam boiler plants according to TRD 604, EN 12952 and EN 12953.

Steam Boilers are pressurized containers that allow the water to be steamed by heating. Steam boilers are produced according to EN 12952 (for Water Tube Boilers) and EN 12953 (for Flame Smoke Tube Boilers) standards in Europe.

We can collect Steam Boilers under two main titles as

• Fire Tube Boilers

         and

• Water Tube Boilers

but Steam Bıilers; can also be named according to the place of use, type of furnace, type of fuel used, its construction, and boiler pressure class.

Feed Water Control, Level Measurement and Safety

Level Measurement and Safety

The boiler drum is where water and steam meet and separate from each other. The water level here is one of the important parameters to be measured and controlled. For the boiler to operate safely and efficiently, the water level in the drum must be kept constant.

Too low water levels can damage the boiler tube due to overheating as a result of the boiler running dry, causing mechanical damage, that is, melts and collapses. The water, which is given without waiting for the hot boiler pipes to cool, causes explosions.

Another point to note is the high level. Too high drum water level can damage downstream equipment, causing water transport, improper operation of separators, difficulty in temperature control, water carryover resulting in water hammer.

The amount of water entering the boiler should be balanced with the amount of steam released to obtain the constant water level in the boiler. Therefore, it is extremely important to have information about the operating principles, assembly requirements, strengths, and weaknesses of the drum water level control system. Ignoring these issues may result in an improper application, frequent maintenance, unsafe operation as well as low system performance.

On-Off Feed Water Control

During the On-Off feedwater control, the feedwater pump turns on and off by the commands it receives from the level probe. The pump starts when the water level drops to the specified low water level. When the water level reaches the determined high water level, the pump stops.

Modulating Feed Water Control (Single Element Control)

During the modulating feedwater control, a capacitive level probe on the boiler transmits the water level to the controller, and the water level is kept constant by providing the required valve opening by the level controller. The valve used in the system can be preferred as 2-way or 3-way depending on the user. In proportional feed water control systems, it is desirable to have a pump running continuously and a valve proportionally allowing water passage. In addition to this system, control can be achieved with direct variable speed pumps without using valves. However, due to reasons such as the cavitation of the pumps at low frequencies, the most applied and problem-free method in the field is the systems installed with valves.

Advantages and Disadvantages

• In On-Off Feed Water Control Systems, with the operation of the pump, a colder water than the water in the boiler is added to the boiler. This addition can cause variable vapor pressure and flow. In addition, the continuous opening and closing of the pump in the long term causes wear and tear on the pumps.
• On-Off Feedwater control systems are very simple in terms of installation and use.
• On-Off Feedwater control systems are suitable for low capacities.
• On-Off Feedwater control systems are affordable.
• In On-Off Feedwater control systems, a separate pump is needed for each boiler.
• If there is a peak steam draft in boilers using On-Off Feedwater control systems, production may stop and slow down due to false alarms. In addition, water carryover along with steam may also cause water hammer and there is a devastating impact in the installation.

Calculation of Heat Required for Steam Generation

Fuel: Natural Gas

Amount of Steam Produced: 12 tons / h

Produced Steam Pressure: 10 bar

Heat required to generate steam: Q = m (hg-hf)

Q (kj): Amount of Heat

hg (kj / kg): Saturated Steam Enthalpy: 2783.4 kj / kg (Saturated Steam Enthalpy at 10 bar Pressure = https://en.viraisi.com/saturated-steam-table)

hf (kj / kg): Feed Water Enthalpy: 356 kj / kg (Suppose the feed water tank is held at 85 degrees: enthalpy of saturated water at 85 degrees)

m (kg / h): Amount of Feed Water: 12.000 kg / h

Q = 12,000 (2783.4 - 356)

Q = 29.128.800 kj

Fuel Amount = Heat for Steam Generation / (Fuel Lower Thermal Value * Boiler Efficiency)

Y: Fuel Amount

Q: Heat of Steam (29,128,800 kj in the previous process)

Hu: Fuel Lower Thermal Value (Natural Gas Lower Thermal Value: 8250 kcal / m ^ 3 = 34.518 kj / m ^ 3)

n: Boiler Efficiency (Suppose a natural gas boiler operating at 91% efficiency with 140 C flue gas temperature)

Y = 29.128.800 / (34.518 * 0.91)

Y = 927.33 m ^ 3 for 12 tons of natural gas

Y = 77.3 m ^ 3 / ton

According to Istanbul Natural Gas Distributor's statements dated 01.07.2019;

Eligible Consumers (300,001 -800,000 cubic meters) = 1.625624 TL / m ^ 3

77,3 * 1,625624 = 125,66 TL / ton = Fuel price for 1 ton of steam is 125,66 TL

In order to be able to find out the actual cost, it is necessary to add the cost of the personnel, which is used in the boiler room, the chemical cost used for water conditioning, the electrical cost, the maintenance cost, the water cost. This means roughly 25% to 30% more to the fuel price.

Saturated Steam Table
Gauge Pressure Pg (Bar g)	Absolute Pressure Pa (Bar)	Temperature T (°C)	Spesific Volume V (m³/kg)	Saturated Water Enthalpy hf (kj/kg)	Evaporation Enthalpy hfg (kj/kg)	Saturated Steam   Enthalpy    hg (kj/kg)
0,00	1,013	100,0	1,673	419,1	2258,4	2677,5
0,05	1,063	101,4	1,601	425,0	2254,2	2679,1
0,10	1,113	102,6	1,533	430,4	2251,2	2681,6
0,15	1,163	105,1	1,471	435,8	2247,9	2683,7
0,20	1,213	106,2	1,414	440,9	2245,0	2685,8
0,30	1,313	107,4	1,312	450,5	2238,7	2689,2
0,40	1,413	109,5	1,225	459,7	2232,8	2692,5
0,50	1,513	111,6	1,149	468,5	2227,0	2695,5
0,60	1,613	113,5	1,038	476,5	2221,5	2698,0
0,70	1,713	115,4	1,024	484,4	2216,9	2701,3
0,80	1,813	117,1	0,971	491,9	2211,9	2703,8
0,90	1,913	118,8	0,923	499,1	2206,9	2705,9
1,00	2,013	120,4	0,881	505,8	2202,3	2708,0
1,10	2,113	121,9	0,841	512,5	2198,5	2711,0
1,20	2,213	123,4	0,806	519,2	2194,3	2713,5
1,30	2,313	124,9	0,773	525,0	2190,1	2715,1
1,40	2,413	126,3	0,743	530,9	2186,3	2717,2
1,50	2,513	127,6	0,714	536,3	2181,7	2718,1
1,60	2,613	128,9	0,689	542,2	2178,8	2721,0
1,70	2,713	130,1	0,665	547,2	2175,0	2722,3
1,80	2,813	131,4	0,643	552,7	2171,3	2723,9
1,90	2,913	132,5	0,622	557,7	2167,9	2725,6
2,00	3,013	133,7	0,603	562,7	2164,6	2727,3
2,20	3,213	135,9	0,568	571,9	2158,3	2730,2
2,40	3,413	138,0	0,536	581,1	2152,0	2733,1
2,60	3,613	140,0	0,509	589,5	2146,2	2735,7
2,80	3,813	141,9	0,483	597,9	2140,3	2738,2
3,00	4,013	143,7	0,461	605,8	2134,8	2740,7
3,20	4,213	145,4	0,440	612,9	2129,4	2742,4
3,40	4,413	147,2	0,422	620,5	2124,4	2744,9
3,60	4,613	148,8	0,405	627,6	2118,9	2746,5
3,80	4,813	150,4	0,389	634,3	2114,3	2748,6
4,00	5,013	152,0	0,374	641,0	2109,3	2750,3
4,20	5,213	153,4	0,361	647,3	2104,7	2752,0
4,40	5,413	154,8	0,348	653,6	2100,1	2753,7
4,60	5,613	156,2	0,336	569,8	2095,9	2755,8
4,80	5,813	157,6	0,325	665,7	2091,3	2757,0
5,00	6,013	158,9	0,315	671,1	2087,1	2758,3
5,50	6,513	162,1	0,292	685,0	2077,1	2762,0
6,00	7,013	165,0	0,272	697,9	2067,4	2765,4
6,50	7,513	167,8	0,255	710,1	2058,2	2768,3
7,00	8,013	170,5	0,240	721,8	2049,0	2770,8
7,50	8,513	173,0	0,227	733,1	2040,6	2773,8
8,00	9,013	175,4	0,215	743,6	2032,3	2775,8
8,50	9,513	177,7	0,204	753,6	2024,3	2777,9
9,00	10,013	180,0	0,194	763,3	2016,4	2779,6
9,50	10,513	182,1	0,185	772,9	2008,8	2781,7
10,00	11,013	184,1	0,177	782,1	2001,3	2783,4
11,00	12,013	188,0	0,163	799,3	1987,1	2786,3
12,00	13,013	191,7	0,151	815,6	1973,7	2789,2
13,00	14,013	195,1	0,141	831,1	1960,7	2791,8
14,00	15,013	198,3	0,132	845,7	1948,1	2793,9
15,00	16,013	201,4	0,124	859,6	1936,4	2795,9
16,00	17,013	204,4	0,117	872,9	1924,7	2797,6
17,00	18,013	207,2	0,110	885,5	1913,4	2798,9
18,00	19,013	209,9	0,105	897,8	1902,5	2800,1
19,00	20,013	212,5	0,100	909,4	1891,6	2801,0
20,00	21,013	215,0	0,095	921,1	1881,5	2802,6
21,00	22,013	217,3	0,090	932,0	1871,5	2803,5
22,00	23,013	219,6	0,087	942,4	1861,5	2803,9
23,00	24,013	221,8	0,083	952,9	1851,4	2804,3
24,00	25,013	224,0	0,080	963,0	1842,2	2805,2
25,00	26,013	226,1	0,077	972,6	1832,7	2805,3

When steam meets a cooler surface, it loses some of its heat. This heat loss experienced by the steam causes the formation of small water droplets formed by condensation of the so-called condensate steam.

Increasing the boiler feed water temperature every 6 ° C can save about 1% energy. Therefore, the recovery of condensate as hot water is very important in terms of energy saving.

At high condensate temperatures, the flash steam generated on the suction side of the electric pumps will cause cavitation, so unlike ordinary pumps, condensate pumps are used.

Vira Condensate Pump does not contain any deteriorating mechanical parts. Level control is done electrically by means of electrodes, not by float. If required, the system can be supplied with globe valve, strainer, solenoid valves and check valves, or simply as the condensate pump itself and as a level measuring system.

Condensate pumps pump high-temperature liquids using condensate, steam or compressed air. The condensate collected in the collector (7) begins to fill into the condensate pump. The solenoid valve (1) located at the top of the condensate pump is in the open position. The solenoid valve (2) in the steam line (5) is in the closed position. As soon as the water level in the condensate pump touches the short electrode (4), the open valve (1) closes and the closed valve (2) opens and the drive steam flows into the condensate pump with its own pressure and discharges the condensate. As soon as the condensate level falls below electrode # 3, the solenoid valve # 1 is reopened and the solenoid valve # 2 is closed. The remaining steam in the condensate pump chamber of the driving steam from the line where the solenoid valve 1 is located is sent to the collector (7) to be converted to condensate. Line 6 is used to return and discharge the condensate formed in the steam line to the collector. Outlet number 8 on the collector is left for ventilation. https://en.viraisi.com/condensate-pump

For detailed informations and contact you can send an e-mail to info@viraisi.com and you can reach products details at www.viraisi.com

The quality of the steam is pronounced by dryness. The dryer the steam supplied to the system, the better the quality.

When the steam produced in the boilers is transferred to the installation, it loses some of its heat when it encounters a cooler surface. This heat loss causes the formation of small water droplets called condensate and the condensate is carried by the vapor pressure circulating in the installation. Steam Separators are products that are used to ensure the dryness of the steam that separates the liquid formed in the installations.

In the vortex type steam separator, wet steam enters into the product and descends downwards by guiding the spirals so as to have maximum friction surface and follows the spirals and leaves the remaining moisture on the spirals and leaves the product. The friction surface is at maximum level.

Vira Vortex Type Steam Separators are highly productive, long-life products with high friction surface where you can easily obtain dry steam. https://en.viraisi.com/steam-separator

     

For detailed informations and contact you can send an e-mail to info@viraisi.com and you can reach products details at www.viraisi.com

Temperature control, which is as important as boiler water levels and conductivity values, is a must in TRD regulation for 24 hours and 72 hours unattended steam boiler applications.

In order to minimize and even eliminate damages and accidents that may occur due to high temperatures, the operating temperature is determined according to the operating pressure of the boiler and the boiler is limited for the highest possible temperature value. Thanks to this process, temperature rise that may occur is prevented.

PT 100 and Thermocouples are ideal products for these processes.

For detailed informations and contact you can send an e-mail to info@viraisi.com and you can reach products details at www.viraisi.com

The purpose of this method is to receive a warning from the predetermined point and to maintain the boiler water level at the desired intervals. This method can be called on-off control system or limit control system. In their most common use, these points, the minimum and maximum points, are the two points in which you want to stay alert between the water level in the boiler and for warning. At the minimum point, the warning is taken before the water falls to the critical level and the necessary precautions are taken without any problems. Likewise, by taking the maximum point, we prevent fluid overflow and thus damage. The received warning is usually transmitted to the controller in the form of an electrical signal, after which the connection is completed according to the application by means of audible, illuminated warnings or devices (such as pumps) to control the system. An electrode group electronic device is used in the measurement.

 

Vira Automatic Level Control Systems have 3 different products which can be called On-Off Control or Limit Control.

• SK 1000 Automatic Level Alarm System https://en.viraisi.com/level-alarm-system
• SK 2000 Automatic Level Control System https://en.viraisi.com/on-off-level-control-system
• SK-T 2400 Boiler Top Automatic Level Control System https://en.viraisi.com/boiler-top-on-off-level-controller-sk-2400-t

 

    

The purpose of this method is to measure how much water is in the boiler or tank and to operate the pump or control valve proportionally according to the measured value.

In this system, the level that is set and the current level difference in the boiler or the measured tank are kept to a minimum value so that the level does not fluctuate continuously at maximum and minimum points. The control is carried out by means of a modulating control valve and a controller connected to it by an electrode. The electrode sends signals to the controller according to the water level and the controller then proportionally controls the control valve after evaluating these signals. Proportional opening / closing is made according to the water level in the boiler and the desired water level is kept constant with very small deviations. In these systems, the pump runs continuously. When the control valve closes, the by-pass valve opens.

Vira Automatic Level Control Systems have 2 different products which we can call Proportional Control.

SK 3000 Modulating Level Control Systems https://en.viraisi.com/modulating-level-control-systems

SD-AY 420 Modulating Level Control Probe, 4-20 mA Transmitter https://en.viraisi.com/4-20ma-level-control-system

 

  

For detailed informations and contact you can send an e-mail to info@viraisi.com and you can reach products details at www.viraisi.com

According to the type of water prepared in the feed water tank, salt and a number of impurities reach the steam boiler. As a result of evaporation, the salinity of boiler water increases. A salt concentration higher than the permissible value causes boiler stone, boiler corrosion and foam formation.

The foam not only prevents heat transfer inside the boiler but also can reach the steam installation. Thus, the desired dry steam cannot be obtained. The quality of steam distributed to the installation decreases and the accumulations of water generated force the fittings. Automatic Surface Blowdown System should be used to prevent this situation. The salinity concentration of the boiler water can be kept below the permissible limit value by discharge via the surface blowdown valve. The conductivity of the boiler water is measured (more saline is more conductive) by means of a conductivity electrode stuck directly into the boiler just below the boiler water level and the desired conductivity value is achieved by discharging the boiler water via a proportional valve. Unlike ordinary surface blowdown systems, the Vira BS4-T system is easy to use and suitable for any application with its heat compensation and 4-20 mA output. With heat compensation feature, it is possible to calibrate at desired temperature and pressure and it is plug and play ease. https://en.viraisi.com/automated-tds-blowdown-system

Some impurities and salts (rust, oil and dirt that may come from the installation) precipitate to the bottom of the boiler to form a sludge layer. Thus, the heat transfer capability of the boiler is reduced and there is a danger of corrosion in the boiler. These foreign substances and salts should be periodically disposed out of the boiler to prevent the formation of the settling layer. For this, Automatic Bottom Blowdown Systems are used. By opening the bottom blowdown valve, pressurized boiler water is discharged from the bottom of the boiler. Vira Automatic Deep Blowdown systems have many features other than ordinary timers. One of the most important features of the DB2 system is that the valve communicates the opening and closing status of the valves. If the normally closed valves are prevented from closing for any reason after being opened, the controller will warn you to take action. Only applications made with timer logic are insufficient in this regard. When more than one DB2 system is connected to the same blowdown line, the controllers communicate with each other and the other does not start until one valve is closed to prevent clogging. DB2 system provides the opportunity to operate for the desired time intervals. https://en.viraisi.com/bottom-blowdown-system

Automatic Surface Blowdown and Automatic Bottom Blowdown are complementary to each other, so both operations are normally required.

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In order to operate the boilers in which steam is obtained, which is a widely used form of energy in the industry, in a safe and economical way, technical rules valid in the European Union have been prepared. These rules were created by the Germans and are called TRD (Technische Regeln für Dampfkessel). These norms can be translated into Turkish as ''Technical rules for steam boilers''.

There are 5 different operating modes mentioned in TRD regulations:

• Permanently supervised operation. In this mode of operation, the technical personnel in charge of the system continuously monitor and adjust the water level and steam pressure in the boiler.
• Partial permanent supervised operation. In this mode of operation, the technical personnel responsible for the system check that the system is operating correctly every two hours.
• Unattended time-limited operation at reduced operating pressure.
• 24-hour unattended operation.
• 72 hours unattended operation.

In the TRD regulations and EN 12953 norms, which safety systems should be used according to each type of operation mentioned above are written. For example; an automatic water level and pressure control is not required in permanent supervised operation; in limited, 24-hour and 72-hour unattended operation, these are compulsory. These safety devices are usually supplied by boiler companies with the approval of the customer. 

As mentioned above, a number of controls are required for safe and efficient operation of the boiler. These controls can be grouped under two main headings: Automatic Level Control Systems and Automatic Blowdown Systems.

Automatic Blowdown Systems

• Bottom Blowdown
• Surface (TDS) Blowdown

Automatic Level Control Systems

• Limit Control (On-Off Control)
• Control by Continuous Measurement (Modulating Control)

Apart from these two headings, temperature control and condensate turbidity control are important controls that should be controlled according to TRD 604 norm.

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The first steam engine (Savery Machine) was invented by the British engineer Thomas Savery in 1698 for the purpose of discharging the water in the mines and it was developed and evolved in many different sectors for different purposes. Today, a derivative of these machines, which are mostly encountered in industry, are steam boilers.

The boiler is a closed and pressurized vessel used to produce steam pressure at a pressure higher than atmospheric pressure. By keeping the steam in this closed container, pressure is obtained, and the pressure increases and the evaporation temperature rises. In this way, steam with high thermal capacity is prepared for transfer.

Boiler types are divided according to their structure, usage area and fuel types.

The boilers are named according to type of material used in the construction of boilers (steel boiler, etc.), the type of fuel used (liquid fuel, gas fuel, etc.), pressure in the combustion chamber (counter-pressure, counter-pressure), heating fluid type (hot water boiler, welding water boiler, etc.), the structural design of the boiler (flame pipe, water pipe, etc.) or the shape of the boiler (semi-cylindrical, fully cylindrical, etc.).

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• It is an ideal heat carrier.
• It can carry more heat with small diameter pipes.
• Environmentally friendly so clean.
• Energy can be saved by recycling.
• The fluid is transported at its own pressure.
• There is no need for a pump for circulation, so the cost is low.
• It is possible to perform temperature control very precisely.
• Steam reduces the risk of corrosion in the installation.
• Due to the transmission of small diameter pipes, heat losses are less than other systems.
• Thermodynamic properties are good.
• Steam is safe, so there is no flammability. It is a sterile fluid.

    

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Steam in the sense of dictionary; Although it means the gas state in which liquids and some solids are transformed by the effect of heat, we can define the part of our interest as water vapor. The term evaporation is a physical term used only for liquids to become gaseous.

Evaporation continues until either the evaporating liquid is over or the air above the liquid is saturated with steam.

The steam applies a pressure on the walls of the container. The higher the temperature, the higher the pressure. As a liquid evaporates, the molecules on its surface get rid of and become gaseous. The dryness of the obtained steam shows how high quality it is.

These evaporating molecules are constantly in motion. During the evaporation of water, a dynamic equilibrium is established in which equal amounts of liquid or solid particles become gaseous and at the same time return from the gaseous state. The vapor that establishes such an equilibrium is called ’saturated steam'.

Due to its physical properties, steam, which is frequently used in industry, is an indispensable part of the industrial sector.

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• Petrochemistry
• Thermal Power Plants through Steam Turbines
• Pharmaceutical and Food Industry for Sterilization Purposes
• Building Materials Industry
• Heating Systems with the help of Heat Exchangers from Steam to Water (Heating Installations)
• Refineries
• Chemical Processes
• Food Industry, such as olive, tea and milk factories
• Sterilization processes
• Fertilizer Industry
• Rubber Products and Manufacturing
• Paper Industry
• Wood Processesing and Shaping
• Tire Factories
• Hospitals
• Hotels
• Iron and Steel Processing Plants

 

    

    

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Calorie: It is the amount of energy that should be given in order to increase the temperature of one gram of water. 1 calorie = 4.186 J.

Steam: As we all know, there are 3 phases of matter. Water is called ice in its solid state, gas in its gas state and water in its liquid state.

Saturation Temperature: The temperature at the point where the water starts to boil under any pressure (point 2 in Figure 1) is called the saturation temperature.

Evaporation Enthalpy: It is at constant pressure and temperature at 2 points where water starts to boil. The heat that converts from point 2 to point 3 is the vaporization enthalpy (Hidden Heat).

Saturated Steam: (point number 3 in Figure 1) The state where the water is completely in the vapor phase, under any pressure and at the saturation temperature at this pressure, is called saturated steam.

Superheated Steam: If the temperature of the steam under any pressure is above the saturation temperature at that pressure, it is called angry vapor.

Dryness: In the case where the liquid and vapor phase of the water is combined, the ratio of the mass of water vapor in the mixture to the total (water + steam) mass is called the degree of dryness.

Dry Vapor: This is the vapor with an X value of 1 in Figure 1. It is a vapor without water.

Wet Steam: It is a steam with water grains.

Condensate: Steam starts to transfer heat with the surfaces it encounters outside of the boiler and gives a part of its enthalpy. In doing so, it turns into water at the same temperature.

Horn Impact: The first contact of the steam coming from the boiler with the cold air is the piping which is cooler than the steam temperature and used for the transportation of steam. The steam transmits a part of its enthalpy to the installation pipes of lower temperature and turns into condensate (water) at the same temperature. If the water accumulated in the installation is not quickly and correctly evacuated, it will damage the plumbing and other installation elements such as valves and elbows by high speed and noise. This is called the Coach Pulse.

TDS (Total Dissolved Solids): means total dissolved solids. The unit is ppm (part per million, ie the amount of solids per million) or mg / liter. It is one of the parameters showing the ion and mineral richness of waters. The more water is soluble in the water (ie the greater the amount of TDS), the greater the conductivity.

Blowdown: The feed water from the boiler contains many dissolved substances (such as salt, lime and iron) and solid suspensions. TDS, whose density increases or hangs as the feed water is evaporated in the boiler, causes considerable inefficiency in the boiler over time. In order to remove these unwanted substances from the boiler to the limits determined in the boiler, a part of the boiler water and the undesired substances are removed from the system is called blowdown.

Bottom Blowdown: The process of dissolving the sediments from the bottom of the boiler together with the boiler water. After this process, water must be added to the boiler. Level indicators are important.

The steam distribution is the bridge between the steam produced and the place to be used. The place of production can be places where a boiler room or heat and electrical energy is produced jointly and even with high heat recovery.

Regardless of the steam produced, the steam must be delivered to the correct amount, quality and at the right pressure. This is carried out with the help of transport pipes.

The steam produced in the steam boiler can be transferred to the installation or interrupted by a control valve. This pipe is opened for the first time during commissioning and starts to pass through the pipes and steam fixtures used for the steam distribution at high temperature and pressure. Since the temperature difference between steam and pipeline is at the highest level, maximum condensation water will occur in the installation until the system enters the regime. Over time, the system will enter the regime, the temperature difference between the steam and the installation and thus the condensation will be minimized. However, the temperature difference between the steam and the installation will never be zero. This means that there will always be a condensation inside the pipe. Extraction of the condensate from the designated collection points is vital for both installation and installation luminaires.

When we went to the other end of the installation, the steam reached the end user (steam-powered machines, heat exchangers, etc.). The steam used here condenses, leaving its temperature on the process that needs to be processed and converted into water at the same temperature.

This cycle becomes continuous. It is necessary to fill the feed water with the softening water coming from the circulating condensate and the water, the feed of this feed water, the heating and vaporization of the water together with the fuel of the burner should be finally distributed.

There is an important point to note. It is the recovery and use of water condensed on processed products and devices. This hot water is a valuable resource. It should not be considered as waste water. It does not need to be reheated and metered, it can be reused as feed water and will save energy.

1- Ventilation from Steam Installations

Air is seen in two ways in the steam installation. The first one is the air that is already in the installation when the first operation is in operation, the second is the air going to the boiler in the condensate water by penetrating into the installation when the steam is cut for any reason.

The evacuation of the air in the steam installation is very important. Since the air is not condensing, it will be discharged from the installation only by a discharge method. The air that cannot be discharged will prevent the desired temperatures in the installation and will lead to corrosion and shorten the life of the installation.

In the main steam lines, the air is discharged from the end of the installation line. The installation of the air thrower is entirely related to where the air thrower is to be installed, or even where the steam comes from. In the case where the steam is supplied from the bottom, it is mounted on top because the air is collected on top. In the case where the steam is given from the top, the air is mounted on the bottom and it is mounted on the bottom.

The air thrower in the steam installation must operate with thermostatic condensate logic. It should not be confused with air throwers used in water installations. Since there is only air and water in the plumbing system, an air pusher with a float system can be released. However, an air thrower must be used in the steam installation depending on the temperature and which interrupts the discharge when the steam temperature is reached.

2- Ventilation from Water Installations

The air and gases in the water installations considerably reduce the heat transfer efficiency. The heat transfer effected by the 1 mm air layer and the effect of a 13 m thick copper wall on heat transfer are equivalent.

In addition, the air and gas accumulated in the water installation significantly reduces the installation life, but also causes noise. It may even cause system crashes and may cause deterioration of armature groups such as valves, meters in the installation.

In order to avoid such situations, the use of automatic air vents is of great importance. Although it is not a special place to use automatic air vents, it can be used at the points where the air can accumulate and at every point where you want to evacuate the air. ( See ... https://en.viraisi.com/viravent-deaerator )