| PRODUCT INTRODUCTION |
| Foreword Scotch Marine fire-tube boiler design in various forms (2-pass, 3-pass, 4-pass, fire-box, dry back, wetback), industry standard, is over 150 years old and has remained largely unchanged since it was first used in ships. Because of the perpetuation of this design, there are too many tubes, lots of refractory, tubesheet cracking and efficiency degradation at part load. There is nothing advantageous in number of passes found in 3-, and 4-pass boiler designs. Number of passes solely means more tubes and more direction reversals for flue gas leading to increased static back pressure. Swiss company Ygnis (www.ygnis.com) introduced 2-pass reverse flue design in 1950's, which showed the way to reduced number of tubes. Clarification of efficiency of boiler operation The simplest and most widely used term for boiler efficiency is called fuel-to-water/steam efficiency. It is calculated from flue gas temperature and composition and jacket losses (the latter seldom exceeds 1%). This is an indirect method. To assess actual economy of boiler operation over a certain period, the so called "input/output" (I/O) efficiency or "boiler efficiency" must be applied, which incorporates all losses of the boiler and burner. This is a direct method. To accomplish this, the energy released from the fuel and energy taken up by the boiler water must be determined. This is more demanding task than indirect method being the reason if its dominance. There is always a difference between these two values, which increases as boiler load is reduced. Even though boilers are designed to cover peak load they almost in all cases operate up to 90% of time at part load. The lower the boiler load, the lower the I/O efficiency and the higher the difference to fuel-to-steam/water efficiency. Efficiency degradation at reduced boiler load can exceed 15%. Boilers have to be designed to cover peak load, and since these seldom appear, boilers generally operate at reduced loads, in many cases far below 50%. This is, besides tube sheet cracking, too numerous tubes in too many passes along with extensive use of refractory lining the biggest drawback of conventional Scotch marine boiler design. New generation of fire tube boilers - WARGA type The new boiler design, called by its designer Warga boiler, offers following unique benefits to the industry: a) minimum number of tubes (75 in 4MW/400HP boiler, down from up to 237 as found in same-sized Scotch Marine designs; b) more than 70% of released heat from combustion being taken up in furnace alone (nearly 100% more than in Scotch Marine design); c) no refractory lining; d) cooled door/wet front design meeting all criteria, applicable also on steam boilers, as well as on double furnace units; e) no efficiency degradation at reduced boiler loads, turn downs, respectively; f) absence of tubesheet cracking by lowered temperature on tubesheet by cooled door; g) common 2-pass platform, industry's first, eliminates various models (3-, 4-pass, dry back, wet back). Performances of WARGA boilers In 1999, Tucson Medical Center (TMC, www.tmcaz.com), Tucson, Arizona, USA installed three Warga boilers of 4MW/400HP 150psi/10bar, 6-ton steam per hour capacity. Customer's old boilers were installed in 1978, and were operated and maintained very well. Boiler are equipped with monitoring equipment (www.rosemount.com), with data logging round the clock. Data indicate a consistent 20.5% increase in seasonal Input/Output boiler efficiency (up to 15 percentage points) over previous boilers of same basic design, or so much fuel used less for same amount of steam generated, respectively. These boilers are also unique from another perspective, namely they are the first of their kind and as such carry unique serial numbers 001, 002 and 003. There was sub 3-year installation payback on fuel savings, with fuel prices as of 2000. Addition of economizers would had further shortened the payback. Hence, over the boiler lifetime of minimum 20 years, the investment in new boilers will be returned several times. No spare parts have been needed to date. Such high fuel savings are also in part a merit of high quality Weishaupt (www.weishaupt-corp.com) dual fuel burner and advanced Autoflame (www.autoflame.com) combustion controls. Summary Warga boiler team picked up where Ygnis left and come up with the utterly upgraded and optimized design built around two pass reverse flue principle. The design is proven free of deficiencies the conventional Scotch Marine design, there is no efficiency drop at part boiler load, there are up to 70% less tubes, and tubesheet cracks as well refractory material are gone. Patented new technical solutions have been proved effective, durable and reliable, with no additional requirements on burner and lesser burden on service and maintenance. No trade-off and no downsides have been observed. It is possible also to retrofit installed conventional boilers, which improves their performance permanently and rids user of problems mentioned above. Since it is industry's first common platform boiler its introduction in the manufacturing is relatively simple and straightforward process. The design and claims have been proven in 10 years continuous operation as of March 2009. The boiler has been named after its designer Warga boiler. |
| TUBE NUMBER COMPARISON |
| Conventional Scotch Marine boiler - characterized by numerous tubes |
| Warga boiler - highly reduced number of tubes (75 in 4MW/400HP boiler) |
| REFRACTORY LINING USAGE COMPARISON |
| Scotch marine boiler - characterized by extensive use of refractory lining at front as well at rear being a heat sink |
| Inner side of cooled door on Warga boiler - no refractory lining |
| IMAGES FROM THE SITE IN USA |
| Warga steam boilers in operation at Tucson Medical Center, Arizona, USA - side view |
| Warga steam boilers in operation at Tucson Medical Center, Arizona, USA - side view |
| Warga steam boilers in operation at Tucson Medical Center, Arizona, USA - front view |
| Warga steam boilers in operation at Tucson Medical Center, Arizona, USA - top view |
| Warga steam boilers in operation at Tucson Medical Center, Arizona, USA - rear view |
| Stack readings at low fire for gas (efficiency calculated with gas higher heating value, add 8.6 for lower heating value) |
| Stack readings at low fire for gas (temperature in degrees of Fahrenheit) |
| Stack readings at high fire for gas (temperature in degrees of Fahrenheit) |
| Stack readings at high fire for gas (efficiency calculated with gas higher heating value, add 8.6 for lower heating value) |
| ADVANCED FIRE-TUBE BOILER TECHNOLOGY |
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