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Orumbayev Rakhimzhan Kabievich, doctor of engineering, professor at Almaty University of Power Engineering and Telecommunications
Kibarin Andrey Anatolievich, candidate of engineering, head of Heat Power Units department at Almaty University of Power Engineering and Telecommunications Korobkov Maxim Sergeevich, Engineer at Almaty University of Power Engineering and Telecommunications E-mail: korobkovmax@gmail.com Khodanova Tatyana Viktorovna, Senior lecturer at Almaty University of Power Engineering and Telecommunications
NEW ASEISMIC HORIZONTAL DESIGN KV-GM-55 HOT-WATER BOILERS OPERATIONAL EXPERIENCE
Abstract: This article is dedicated to problems involved in the design of efficient aseismic hot-water boilers. Authors have suggested using the horizontal aseismic design of 35-55 MW capacity KV-GM hot-water boilers in seismically active areas, and to install them inside small boiler houses. According to the extrapolation of experiment data, the temperature of exhaust gases under nominal load equaled to 160 °C, whereas gross efficiency rate of the boiler was about 92.5%.
Keywords: hot-water boiler, heating tests, bi-radiated screen, radiative and convective heat transfer, reliability increase, operational efficiency.
Currently, there is a big number of medium capac- maintenance of tower hot-water boilers, companies
ity hot-water boilers with outdated design are being had to have a high building to be built next to the
used across the whole Republic of Kazakhstan, and boiler, and in the seismically active areas, where the
which have low efficiency (89-90%) and reliability seismic activity reached 9 points of intensity, such
rates. Main designs of KV-GM and PTVM hot-water boilers were equipped with aseismic supporting
boilers were created in the middle of the previous cen- structures and that caused sufficient increase of con-
tury [1]. New KV-GM-55-150 hot-water boilers with struction costs. That's why authors have suggested
the horizontal design were created by authors due to KV-GM-55-150 hot-water boiler with an aseismic
the technical assignment received from LLP "Almaty horizontal design for highly seismic areas, where
teplocommunenergo" (LLP "ATCE"), which wanted boilers are to be installed inside the buildings with
to increase the power rates per unit and it was also 9.0 m ceilings or lower.
just about time to substitute outdated PTVM-30MS, Hot-water boiler with the new design had it's
PTVM-50 and PTVM-100 boilers as well. lower headers (chambers) resting on the basement
Serial PTVM boilers have tower design and using special "sliding" supports with convective part
big height of up to 17.6 m. In order to perform the of the boiler attached to them.
1 - two supplying pipes, 0327 mm each; 2 - lower front header; 3 - lower r - shape all-welded screen; 4 - ceiling r - shape screen; 5 -upper back header of the furnace; 6 - upper separation walls located in the dead middle of the boiler; 7 - two symmetrical r - shape front headers; 8 - front bypass symmetrical headers; 9 - two symmetrical all-welded side screens; 10 - first upper U -shape symmetrical bypass pipes; 11 - all-welded back screen with lower furnace outlet screen; 12 -lower all-welded screen of the first convective part; 13 -vertical intermediate all-welded screen with upper furnace
outlet screen, located between the first and the second convective parts; 14 - upper all-welded screen, located above the first convective part; 15 - second upper U - shape symmetrical bypass pipes; 16 - symmetrical convective packs of U - shaped pipes with checkered placement pattern at the first convective part of the boiler; 17 - symmetrical convective packs ofU - shaped pipes with checkered placement pattern at the second convective part of the boiler; 18 - upper third U - shaped symmetrical bypass pipes; 19 - r - shaped all-welded back screen; 20 - two symmetrical outlet pipes, 0327 mm each; 21 - upper symmetrical side headers with the upper separation walls that divides the first and the second convective parts in half; 22 - upper header with central separation wall of the vertical intermediate all-welded screen with upper outlet screen; 23 - lower drainage valves; 24 - two symmetrical gas and fuel oil torches
Figure 1. Hydraulic scheme of KV-GM-55 hot-water boiler
Lower headers of side screens are attached to the basement by means of anchor bolts. Expansion of the furnace due to the heating is directed towards the front face, whereas expansion of convective back part is directed towards gas duct. The gas duct of the boiler is equipped with thermal compensator and the second part expands freely towards the back face ofthe boiler.
General hydraulic scheme of KV-GM-55 hot-water boiler is shown on figure 1 and protected by active Patents of the Republic of Kazakhstan [2; 3]. Water circulation within boiler design in accordance with [2] is performed by means ofparallel flows with overall water consumption of up to 658(700) m3/hour, 329(350m3/hour) through each symmetrical side of the hot-water boiler, starting at the furnace and going along the whole convective part of the boiler. Coming through the feeding pipes, the water is supplied symmetrically on both sides into the lower front header and then goes through the lower screen, then rotating screen and after that, it is fed towards the front part of the boiler through ceiling screen and then the water falls down through the front screen.
By means of bypass headers of the front screen, the left portion of the flow is supplied into the left side screen, and the right portion of the flow is supplied into the right side screen. Equal water flows circulate 5 times through the left and the right side screens and after that this water is fed into the back outlet screen of the furnace, then, through two symmetrical halves, two flows are falling to the lower outlet header. From the lower outlet header two flows travel through the lower screen of the first con-vective part and then go up through the intermediate outlet screen to its upper header, and from there the flow comes back to the second upper header of the first convective part via the upper screen. From the second upper header the left portion of water flow goes down through the left convective pack of tubes, and the right portion of water flow goes down through the right convective pack of tubes in the opposite direction to combustion products, and the amount of tubes that go along with the direc-
tion of water flow decreases in order to increase its speed in the high-temperature area of furnace gases exhaust. In the lower side convective headers, two flows go through bypass pipes and supplied into the second convective part, where these two flows move up through convective tubes, amount of which decreases in order to increase the speed of water in the opposite-direction pipe in relation to the lowering gas flow. From the side upper convective headers, two water flows travel down into the upper header of the back screen, from where they are then going down into the lower back screen via parallel T-shaped pipes and extracted beyond the boiler. Fill with new KV-GM-55-150 hot-water boiler with water volume (23.2 m3) is performed when all air outlet valves are open. Valves are installed between rising and dropping water lines. During the wash of hot-water boiler, all the sludge and slit is being removed from the lowest points via the drainage valves.
There are two PGMG-30 fuel-oil and gas torches installed on the front screen in a parallel manner, which rotate horizontally towards the back of the furnace, washing the tubes of rotating screen in perpendicular motion, then, the gas flow from burners touches the all-welded tubes ofback screen and goes through tubes of lower outlet screen coming under the convective pack of tubes of the first convective part. After that, the gas flow rises and through the opposite direction flow line washes convective tubes that are located in the first convective part and have a checkered pattern of placement, then, in the upper part gas flow goes through divided pipes of intermediate outlet screen and travels down flowing around the convective tube arranged in a checkered pattern located in the second convective part, then gas flow travels through gas line that is equipped with thermal compensator, and after that gas is extracted beyond the boiler.
The first KV-GM-55 boiler was put into operation in October 2011 and was adjusted to water consumption rate of G = 658 t/hour, (t1 =63 °C, t2 += = 128 °C, texh=154 °C), the hydraulic resistance ofthis boiler was about 0.23 MPa, and the efficiency rate was
about 92.86% under 49.61 MW heating capacity. According to the demand of micro-districts located around the "Akselkent" (Almaty city) boiler house, the heating load of the boiler was corresponding to design indexes. Testing results and operational indexes appeared to be almost identical to design indexes calculated by engineers, who designed the boiler, and almost identical to project indexes as well.
The new arrangement of two convective parts that have 032 x 3 mm tubes and located next to each other, was implemented in similar designs of horizontal hot-water boilers, such as KV-GM-35, KV-GM-40, and KV-GM-50. The front, upper, lower, rotating, back and two side screens allowed to create the symmetrical structure [2; 3]. Screens were made in an all-welded manner, and the membranes (fins) were consequently moved to the opposite sides from the center plane by s/d = 1.4 (d = 57 x 4 mm) in accordance with [4]. All-welded separation panel had eleven or thirteen tubes, and each twelfth or fourteenth tube were interconnected by fins with the asbestos insulating plate between them, and they were not welded. The separation walls (fins) of furnace screens were consequently moved to the opposite sides from the centerline plane in order to provide more uniform heating across the whole perimeter of screen tubes. All-welded screen with separation walls that were consequently moved away from the centerline plane [5] is forming the rigid structure. Being assembled in such a manner screens provide sufficient density in the furnace and strengthen the structure ofboiler, also making it almost immune to cracks and pops inside the furnace volume and to changing heating loads.
Table 1 - KV-GM-55 hot-
KV-GM-55 boiler was operating for seven heating season in automatic mode along with the auxiliary equipment (APCS - Automatic Processes Control System) and maintaining the fuel oil handling equipment of the boiler house in operational condition. There were still no changes, deformations, leaks or water condensation on screen tubes surfaces or tube packs or headers observed up to the present.
In order to perform heating tests of the new KV-GM-55-150 hot-water boiler No.5 at the "Akselkent" boiler house, there were preparatory works done to the unit, which included the installation of additional gauges, gas analyzing unit with digital duplication (APCS) ofboiler characteristics measured in five modes of heating capacity in accordance with typical testing methods.
During the process of testing, boiler's heating capacity was ranging from 25.18 to 49.6 MW, the consumption rate of the 8289 ccal/m3 gas was ranging from 2700 m3/hour to 5566 m3/hour. The excess of air a in the content of exhaust gases was ranging from 1.36 to 1.16 accordingly. The quality of combustion was constantly controlled by the gas analyzing unit.
Main thermal characteristics of the new KV-GM-55 boiler with a horizontal design, which were obtained during operational testing, are shown in (table 1).
Extrapolation of testing results shows that the temperature ofoutlet gases under nominal load would be 160 °C, whereas the gross efficiency rate of the boiler would be 92.5%, which is significantly higher than the same parameters of boilers currently used in the JSC "ATCE" system of boiler houses [1; 5]. iter boiler testing results
Parameter Mode 1 Mode 2 Mode 3 Mode 4 Mode 5
1 2 3 4 5 6
Heat production rate, MW, 25.95 36.63 43.5 45.79 49.6
Gas pressure, kgf/cm2 0.051 0.087 0.126 0.139 0.167
Water consumption of a boiler, t/hour 658 658 658 658 658
Air pressure in torches (mm water column) 125 104.7 158 177 208
Inlet/Outlet water temperature, °C 55/89 63/111 63/120 63/123 63/128
1 2 3 4 5 6
Gas consumption acc. to gauge, m3/hour 2915 4023 4803 5076 5566
Boiler's hydraulic resistance, MPa, (R Rout) kgf/cm2 0.35 (11; 7) 0.35 (11; 7) 0.35 (11; 7) 0.35 (11; 7) 0.35 (11; 7)
Efficiency rate, natural gas operated,% 93.73 93.69 93.34 93.06 92.86
Outside air temperature, ° 15 15 15 15 15
02 content in exhaust gases,% 5.3 3.1 3.6 3.5 3.2
Discharge pressure in furnace, Pa 30 30 30 30 30
Temperature of exhaust gases, °C 115 133 140 147 154
Heat losses with exhaust gases q 2,% 5.29 5.61 6.07 6.38 6.63
Heat losses into environment, q 5% 0.98 0.70 0.59 0.56 0.51
Specific consumption rate, kg, spec.t/Gcal 152.42 152.48 153.05 153.81 153.84
Nowadays there are three KV-GM-55 hot-water boilers with a new design and six KV-GM-35 and KV-GM-40 hot-water boilers operating in Almaty city.
Authors and boiler engineers have recently perfected designs of KV-GM-55, KV-GM-35, and KV-GM-40 hot-water boilers, they have considered all features and notices obtained from organizations, which were using these boilers. The furnace chamber was equipped with additional two-row wrapping screen, which plays the role of additional radiative surface and intensifies the ignition of gas torches. The efficiency of using bi-radiated screens in hot-water boilers was thoroughly reviewed in the following works [6; 7; 8]. Technical characteristics of the boiler were raised to the following indexes: radiative heating surface Had = 286.7 m2, convective heating surface H = 1406 m2, furnace volume V , = 313.3 m3.
conv ' rad
The installation of the additional two-row wrapping screen before the rotating screen at the end of the furnace caused the significant increase ofboiler's heating characteristics due to intensification of heat transfer, and to decrease the temperature of exhaust gases behind the boiler along with the increase of boiler's efficiency rate [3] up to 93-93.5% under nominal load.
Nowadays, within the grant financing by Committee of Science of Ministry of Science of the Republic of Kazakhstan for the proj ect AP№ 05133388, the compilation of experience gained due to the
operation of new efficient hot-water boilers with medium and low heating production rates using the KV-GM-40, KV-GM-35, KV-GM-55, KV-GM-7.56, KV-GM-3.65 and KSGn boilers as an example.
Conclusion
New generation hot-water boilers KV-GM-55, KV-GM-40, KV-GM-35 are successfully operating within the system of LLP "ATCE", and if speaking about the main characteristics, these boilers surpass boilers with similar designs.
Results of thermal testing have confirmed main calculated parameters pre-defined by engineers in the design of KV-GM-55 horizontal hot-water boiler. The gross efficiency rate of the boiler under nominal load would be 92.5%. The operational experience has shown that during the process ofboiler operation it is possible to maintain a high rate of efficiency and low rates of harmful exhausts and greenhouse gases.
Considering the operational experience, notices and remarks obtained from organizations used these boilers, and thermal tests, the design of hot-water boiler was improved - furnace chamber was equipped with additional two-row wrapping screen, which allows increasing heating characteristics of boiler significantly, and raising the design efficiency rate of the boiler up to 93-93,5% under nominal load.
References:
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4. Patent of the Republic of Kazakhstan. No. 11229. Hot-water boiler. Orumbayev R. K., Chizhov V. E. and etc. Published bulletin No. 2. 15/02/2002.
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