András Balogh and Zoltán Szabó
GEA EGI’s experiences & achievements in the field of water conservation type cooling systems
EGI in Hungary started its dry cooling activity nearly six decades ago, when indirect dry cooling for power plant applications was initiated by late Professor Heller, who founded EGI. In wider sense all indirect dry cooling may be referred to as the HELLER System, though the most efficient HELLER System applies to the direct contact
(DC) condenser.
By now the total power plant capacity equipped with this system System exceeds 25 000 MWe, with reference plants are located in 20 countries and include:
» units operating under extreme ambient conditions: e.g. over the arctic belt with air temperature of -62°C or in sizzling deserts of +50°C, as well as in sites located at sea shore or at high altitudes up to 2000 m;
» the largest dry cooled Combined Cycle Power Plant in the world (Fig. 1);
» the only dry-cooled nuclear power plant in the world (4×12 MWe Bilibino NPS in Russia);
» natural draft dry cooling towers through which flue gases of coal fired power plants are exhausted
» cost efficient, environmentally compatible dry/wet derivatives of the HELLER System: 770 MWe equipped with supplemental spraying and 4300 MWe with parallel wet assisting or delugable cooler cells.
These plants provide a solid basis, both technically and economically, to develop the adequate cooling system for any unit rating and any climatic conditions. HELLER Systems are applicable for all kinds of steam cycles of fossil fuelled or nuclear power plants, as well as having the ability for cooling solar power plants [2],[3].
What is the HELLER System?
In a HELLER System the power plant waste heat is initially exchanged in a condenser (preferably in a DC one) to a closed cooling water circuit. The heat absorbed by the water is rejected to the ambient air in fine tube type heat exchangers. The moving air can either be natural, or fan assisted. (Fig.2).
If a DC condenser is used, then cooled water from the cooling tower flows through recuperating hydraulic turbines connected in parallel (or throttling valves) and is used in the DC jet condenser to condense exhaust steam from the turbine. The mixed cooling water and condensate is extracted by CW pump sets from the hot-well of the condenser. About 2-3 % of this flow – corresponding to the amount of condensates – is fed back to the boiler feed water system by simple booster pumps, taking water from the CW pump discharge branch (alternatively from the return CW line prior to entering the recovery hydro turbine). The major part of the flow is returned to the natural or mechanical draft dry cooling tower, where the cooling duty is performed by the so-called “cooling deltas” (water-to-air coolers) grouped in parallel sections. [1],[2],[3]
The Main Components of HELLER System are:
» Condenser – surface or direct contact (DC) jet condenser. In most of the cases DC condenser is suggested since its terminal temperature difference can be as low as 0.3-0.6°K that is for a given cooling tower rating, a better vacuum can be obtained than with a surface condenser (where it is usually 3-5 ° K). However in special cases such as nuclear power stations or various power units serving district heating networks, a surface condenser is applied.
» Hydro-machine groups. If the cooling system has a surface type condenser, regular CW circulating pumps are used. In the case of DC condensers generally two or three (for units larger than 600 MWe) identical hydraulic machine groups, connected in parallel are incorporated into the CW system. Each consists of a cooling water circulation & extraction pump, a recovery hydraulic turbine and a driving electric motor, mounted on a common shaft.
» Draft options for air moving equipment. The HELLER System allows the use of either natural (Figs. 3 & 4) or mechanical draft (Figs. 5 & 6) (unlike the direct ACC, where only mechanical draft can be applied). For medium and large capacity power units, natural draft results in significantly better economics. The natural draft tower shell can either be of the usual reinforced concrete type (Figs 1 & 3), or a structural steel tower with aluminum clad (Fig. 4). For coal fired power plants flue gases can be exhausted through the natural draft tower – using a stack of approx. 40-50 m high instead of a tall chimney. This not only results in capital cost saving but also dramatically reduces the ground level concentration of pollutants [4],[6],[7]. For mechanical draft cooling systems we prefer to supply induced draft fans instead of forced draft ones – to reduce warm air recirculation (Figs. 5 & 6).
» Air coolers. A great variety of water-to-air heat exchangers applicable for HELLER System. For power cooling tasks the best is the so-called Forgó-type; a plate-fin-and-tube, surface treated, all aluminum water-to-air heat exchanger of which different geometries are available. For some special applications Forgó-type heat exchangers are also supplied with carbon or stainless steel tubes and aluminum fins. Heat exchanger bundles, arranged in a V shape, form the assembly units, so-called “cooling deltas”.
The cooling deltas are grouped in parallel sections.
Dry/Wet HELLER System Options
GEA EGI has developed several cost effective dry/wet combinations derived from the all dry HELLER System aimed at improving environmental compatibility and water conservation issues relative to wet cooling; and increasing summertime heat rejection capabilities – and therefore also also turbine output (or reducing investment costs) relative to dry cooling. HELLER System is well suited to dry/wet combinations, as at lower ambient temperatures it is capable to establish in dry operation mode the same vacuum than a wet cooling plant.
Water conservation features of different dry/wet cooling systems can be classified by their annual water consumption referred to an all wet cooling system. [1],[2],[4]
Dry HELLER System with Supplemental Spraying (1-3%)
Supplemental spraying is used for peak-shaving in the hottest summer hours as well as improving plant availability at excessive conditions or in emergency cases (Fig. 5). Thus spraying is applied only for limited time period with quality water needed.
HEAD (Delugable) Cooling System (1-20%)
A further well-proven solution is the HEAD Cooling System (HELLER EGI Advanced Dry/Deluged). The system operates fully dry for a significant part of the year except during the summer hours coinciding with peak power demand. Then, an even water film (deluging) is applied on the special plate fins of the air cooled heat exchanger. The applied quantity of water is significantly more than the evaporation; therefore the excess water is collected and re-circulated after the addition of the necessary make-up. An interesting variant is when a large all-dry natural draft cooling tower is supplemented with mechanical draft dry/deluged HEAD cells to enhance summer capability. These cells can be located either inside or outside of the tower.
In the latter case for plants operating in areas of severe winter climate, the same cells can be used as so-called pre-heaters during the start-up period, ensuring a freeze-proof start even under the most unfavorable winter conditions.
HELLER System with assisting wet cells (5-40%)
A new brand of efficient dry/wet systems has been developed by integrating the dry HELLER System with evaporative cooling cells. The integration can be in parallel through a combined surface and DC condenser or through a surface condenser having separate sections assigned for the closed dry cooled circuit and the wet cooled one. Also they can be integrated either in parallel or in series via water-to-water heat exchangers for transforming the heat dissipation of the wet tower to the closed dry circuit. These systems offer great operational flexibility, high availability and, much better environmental compatibility than the wet cooling tower and remarkably lower investment cost and improved summertime heat rejection than all-dry cooling plants.
Summary
» A completely closed and pressurized cooling circuit, where vacuum is limited to the small space of DC or surface condenser.
» The intermediate cooling water circuit supports flexibility in tower when looking at distance and arrangement wise, without major cost or auxiliary power penalties.
» A sectioned air cooler arrangement is used and easy & efficient online air cooler cleaning is ensured.
» Air moving either by mechanical or natural draft as well as steam condensing by surface or DC condenser can be applied.
» Natural draft allows the exhaust of flue gases via the cooling tower (stack-in-tower and FGD in tower slutions) resulting in capital cost saving and meanwhile dramatically reducing ground level concentration of pollutants.
» The DC condenser and natural draft tower shell support high thermal efficiency and they are practically maintenance-free with 100% availability.
» A variety of air coolers (material and surface wise) are available. The preference is for applying the FORGO-type mono-metal, all-aluminum air coolers for 40+ years life-span, withstanding external and internal corrosion, no flow accelerated corrosion (FAC), adequate for OT water chemistry.
» The conventional condensate extraction pumps can be substituted by simple booster pumps with an alternative connection to the return cold line allowing to remain within resin temperature limit of CPP (i.e. in the most common cases 60 °C) even at max. ambient temperatures.
» The large volume of water in the dry cooling circuit provides buffering condensate capacity as well as adequate conditions for CPP; and by its high thermal inertia can efficiently counter the negative effects of wind gusts (stabilizing back-pressure, thus avoiding surprise turbine trip at excessively warm ambient conditions).
» The extra condensate volume in the DC condenser hot-well allows primary frequency control of supercritical cycles by condensate throttling.
Comprehensive assesment of cooling systems
It is important to identify the most economically viable cooling system as the decision has long lasting consequences – not only on the economics of the power plant – but also through its environmental impact on the surrounding area.
The best approach when selecting the most promising cooling solution is a comprehensive evaluation based on economic life-cycle issues. For comparing cooling systems and their impact on the cost items of the complete power plant shall be determined – alongside the investment costs, the operation and maintenance costs and the effect of the equivalent unavailability (particularly important is the effect of cooling systems’ characteristics upon power output, year round generation, auxiliary power-and water consumption). [1], [2], [5]
The results of such a comprehensive evaluation created a cooling systems serving an 800 MWe CCPP are introduced by Figs. 7 & 8 and showing the so-called economic viability envelopes (the relative economics of water conservation type cooling systems against wet cooling in the coordinates of two vital factors: specific electricity price and specific water price).
The all-dry HELLER System can extend significantly the economic viability of dry cooling (Fig. 7) and the dry/wet derivatives of HELLER System help to stop further areas from wet cooling (Fig. 8).
Another case study was put together for investigating cooling systems serving a 900 MWe supercritical coal fired power unit. Here the final results – presented in the form of a bar chart (Fig. 9) – show a massive reduction in costs of the all-dry natural draft HELLER System compared to a direct ACC.
Conclusions
» The indirect dry cooling HELLER System and its dry/wet derivatives have successfully demonstrated their reliability and effectiveness.
» Given the long lasting impact o a cooling method for a power plant and even on the surrounding area, iIs is important to compare the lifecycle v cost issue.
» Evaluations show how the advanced HELLER System extends the economic viability of water conserving cooling. The natural draft HELLER System can be competitive on present value basis against wet cooling even at a medium cooling water make-up cost.
Literature References
[1] Balogh, A., Szabó, Z., The Heller System:
The Economical Substitute for Wet Cooling, Journal of Power Plant Chemistry,
Vol. 11, No. 11 (Nov. 2009), p 642-656
[2] Balogh, A., Szabó, Z., Heller System:
The Economical Substitute for Wet Cooling – to avoid casting a shadow upon the sky, EPRI Workshop on Advanced Thermal Electric Power Cooling Technologies, July 2008, Charlotte (NC)
[3] Hogan, M.,:
The Secret to Low-Water-Use, High-Efficiency Concentrating Solar Power, Climate Progress, April 2009,
http://www.worldchanging.com/archives/009802.html
[4] Balogh, A., Szabó, Z., The Advanced HELLER System: – Technical Features & Characteristics, EPRI Conference on Advanced Cooling Strategies/Technologies, June 2005, Sacramento (CA)
[5] Balogh, A., Szabó, Z.,:
Advanced Heller System to Improve Economics of Power Generation, EPRI Conference on Advanced Cooling Strategies/Technologies, June 2005, Sacramento (CA)
[6] Takács, Z.,: Flue Gas Introduction – Advantages of Dry Cooling Towers, 5th Int. Symp. on Natural Draft Cooling Towers, May 2004, Istanbul
[7] Szabó, Z.,: Cool for Coal, Journal of Power & Energy 1st quarter, 2004 – Asia Pacific Development
Contacts
Сита Янош/Janos Szita, директор по маркетингу в СНГ,
«GEA-EGI»моб. +36 30 914 2273
тел. +36 1 225 6213
факс + 36 1 225 6193
e-mail: janos.szita@geagroup.com
Адрес:
GEA EGI Contracting/Engineering Co. Ltd.,
Science Park,
Building „B”,
4-20 Irinyi J. u.
1117 Budapest,
Hungary
Вишняков Сергей Васильевич,
директор ООО
«ПИИ «Экодельта»,
моб. +7-912 24 87 515
тел./ факс: (34377)3-13-09
e-mail: ekod2@mail.ru и ecodelta@uraltc.ru
Адрес:
624250, г. Заречный,
Свердловская область,
ул. Алещенкова,
22а.
