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The Steamstar SuperPlus™

is a packaged, natural gas fi red, condensing steam boiler having 102% thermal effi ciency on NCV of natural

gas. To achieve maximum heat recovery, this packaged boiler consists of six passes of fl ue gas, namely three passes in the evaporator, and a single pass in the econ-omizer, non-condensing water pre-heat-er, and condensing water pre-heater.

Combustion products of natural gas comprise gases such as carbon dioxide, wa-ter vapor, nitrogen, and traces of other inert gases. The latent heat of condensation of the water vapor is recovered in condensing sec-tions of Steamstar SuperPlus™ making it a 102% thermally effi cient steam boiler. The report provides details of the STEAMSTAR SUPERPLUS™ indigenously developed and installed by Transparent Energy Sys-tems PLtd. at the fully owned subsidiary of

a German company in India. Performance parameters of the boiler were certifi ed by Petroleum Conservation Research Associa-tion (PCRA), India, per BS-845-Part I.

CONSTRUCTION OF STEAMSTAR SUPERPLUS™

As shown in Figure 1, the Steamstar Su-perPlus™ comprises three passes of heat recovery in a smoke-tube type boiler, fol-lowed by a fourth pass of heat recovery in

TRANSPARENT ENERGY >

102%INDIAN COMPANY PUTS ITS NEW BOILER TO THE EFFICIENCY FIELD TEST

FIGURE 1. A SCHEMATIC DIAGRAM SHOWING CONSTRUCTION OF THE STEAMSTAR SUPERPLUS™.

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Process systems Design & Fabrication

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T O D AY ’ S B O I L E R F A L L 2 0 1 3

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the economizer, a fi fth pass of the non-condensing water preheater, and sixth pass of the condensing preheater. On the fl ue gas side, the condensing preheater is followed by an externally supported stack with material of construction, carbon steel with internal FRP lining, or stain-less steel conforming to IS 6533.

Steamstar SuperPlus™ is equipped with a reliable fl ue gas side condensate handling system. It comprises a SS- or FRP-lined condensate collection and neutralization tank equipped with condensate transfer pump and automatic level controller. When fl ue gas is cooled below dew point, the fl ue gas water vapor is condensed in the con-densing preheater. The pH of condensate from fl ue gas from natural gas combustion has pH values in the range of 3.0–4.5.

To achieve longer life of heat transfer surfaces, a suitable corrosion resistant grade of stainless steels, AISI 304, is used for construction of fl ue gas path and heat transfer surfaces. Also, adequate access is provided to facilitate maintenance, clean-ing, and repairing of heating surfaces. In order to reduce corrosion of heat transfer surfaces, a pressurized deareator tank

is provided to remove dissolved oxygen from feed water by steam sparging. Also, an automatic continuous chemical doz-ing system is provided.

The boiler can be designed to suit condi-tions such as 0 to 100% condensate return from process. The boiler has fl exibility in op-eration so that the same boiler could be oper-ated through a fuel shift from natural gas to FO/LDO/HSD by bypassing condensing pre-heater and by operating the fl ue gas diverter valve and feed water bypass arrangement.

WORKING PRINCIPLEBoiler feed water is preheated in three stages: condensing water preheater, non-condensing water preheater and econo-mizer. Flue gas at the outlet of a smoke tube type evaporator section passes through the economizer section to heat the boiler feed water preheated in the non-condensing water preheater. Fur-thermore, the fl ue gas passes through the non-condensing water preheater to heat the boiler feed water preheated in the condensing water preheater such that the fl ue gas is cooled just above its dew point temperature of 57°C. Then the fl ue gas passes through the condensing water preheater to heat the boiler feed

water from 30°C to 35°C such that fl ue gas is cooled below its dew point tempera-ture up to 47°C.

In this way, the latent heat of con-densation of water vapors present in fl ue gas is recovered to enhance the thermal effi ciency of the boiler up to 102%. Optionally, when the air pre-heater is provided, it further improves the effi ciency of the Steamstar Super-Plus™ up to 103%.

The same boiler could be operated

through a fuel shift from natural Gas to

FO/LDO/HSD by by-passing the condens-

ing preheaterand by operating the

fl ue gas divertervalve and feed water bypass arrangement.

INSTRUMENT PARAMETER MEDIUM

FLOW METER WITH TOTALIZER FLOW • STEAM, FEED WATER, FUEL

• FLUE GAS CONDENSATE (OPTIONAL)

THERMOCOUPLE TEMPERATURE

• STEAM • FEED WATER AT INLET TO ECONOMIZER• FEED WATER AT INLET TO BOILER• WATER AT INLET TO DEAERATOR TANK• FLUE GAS AT BOILER OUTLET, ECONOMIZER OUTLET & WATER PREHEATER OUTLET• WATER AT INLET & OUTLET TO WATER PREHEATERS

PRESSURE GAUGE PRESSURE• STEAM AT OUTLET OF EVAPORATOR• FEED WATER AT INLET OF ECONOMIZER • FEED WATER AT INLET & OUTLET OF WATER PREHEATERS

OXYGEN SENSOR OXYGEN • FLUE GAS OXYGEN CONTENT

MODEL STEAMSTAR SUPERPLUS™ 6000

FUEL NATURAL GAS

CAPACITY 6000 KG/HR (F&A 100)

SAFETY VALVE SET PRESSURE 10.54 KG/CM2(G)

APPLICATION STEAM FOR PROCESS USE

THERMAL EFFICIENCY ON NCV OF FUEL 104%

TABLE 1. DETAILS OF PERFORMANCE MEASURING SYSTEM.

TABLE 2. TECHNICAL SPECIFICATIONS OF THE INSTALLATION.

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The fl ue gas from combustion of natu-ral gas has better characteristics as com-pared to fl ue gas from fuel oils:

• Higher percentage of water vapors in fl ue gas. This allows higher heat recovery in condensing preheater.

• Higher fl ue gas dew point. This offers a thermodynamic advantage in recov-ering heat in multiple stages such as condensing preheater, non-condens-ing preheater, and economizer.

• Higher pH of fl ue gas condensate. High pH value of condensate does not demand usage of expensive corrosion resistant materials for construction of heat transfer surfaces.

PERFORMANCE MEASUREMENTThe Steamstar SuperPlus™ is equipped with a continuous online real time mea-surement and recording system com-prised of instruments shown in Table 1.

The performance tests of Steamstar Su-perPlus™ can be carried out by two methods:

• Thermal effi ciency measurement by direct method of enthalpy difference across boiler (steam to fuel ratio).

• Thermal effi ciency measurement by indirect method as per BS-845-part I & II.

CASE STUDYBased on above mentioned principles and mode of construction, a commercial-scale Steamstar SuperPlus™ was built in year 2011 for a fully owned subsidiary of a Ger-man pigment processing company having a process plant in Gujarat, India. Table 2 gives the details of the installation.

The performance trails were con-ducted by both direct as well as indirect method. The Table 3 accompanied by

the graph shows the performance of the Steamstar SuperPlus™ in terms of over-all thermal effi ciency vs outlet tempera-ture of fl ue gas.

The thermal effi ciency measurement of Steamstar SuperPlus™ was made us-ing indirect method as per BS-845-part I. The performance trials were witnessed and certifi ed by the Petroleum Conser-vation & Research Association (PCRA) of India. TB

TEMPERATURE OF FLUE GAS AT THE OUTLET OF HEAT RECOVERY UNIT (DEG C)

OVERALL THERMAL EFFICIENCY, ON LHV BASIS IN %

OVERALL THERMAL EFFICIENCY, ON HHV BASIS IN %

183 92 83.1

120 95 85.8

99 96 86.7

78 97 87.6

57 98 88.5

55 99 89.4

53 100 90.3

51 101 91.2

49 102 92.1

47 103 93

44 104 94

TABLE 3. OVERALL THERMAL EFFICIENCY VS OUTLET TEMPERATURE OF FLUE GAS.