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A GIA, pe Agenda item II.A.2 (b)

GEOTHERMAL POWER DEVELOPMENT AT ,

H. Christopher H. Armstead *

New Zealand's goethermal power scheme at an earlier project, now abandoned, to install a Wairakei has been generating power since November chemical distillation plant at Wairakei, taking steam 1958. The load carried is 65 MW or more, and outputs at 50 lb/sq in. gauge and exhausting at * lb/sq in. up to 101 million kWh per week have been generated, gauge. This plant, which was to have been combined equivalent to about 12 per cent of the total energy with topping sets on the upstream side and condens- production in . The authorised installa- ing sets on the downstream side, was cancelled after tion of 192 MW was sanctioned in two stages. The the associated turbo-alternators were in an advanced first (69 MW ), completed in March 1960, makes use state of manufacture, and its place was taken by of bore steam only and employs seven small turbo- two IP back-pressure sets.1 But for this historical alternators of approximately 6* MW and 11 MW complication a simpler arrangement of plant would ratings. The second stage (123 MW), now under have been chosen. Direct bore steam enters the construction, will introduce to a limited extent the station at two pressures, as shown, and the hot water use of hot water in addition to bore steam; it will will be partly flashed into steam at 50 and at t lb/sq also be partly served by larger (30 MW ) turbo- in. g. To retain as far as possible an undisturbed alternators., balance of steam flows when any set in the A station Figure 1 shows the thermal field where some is out of service, bypass reducing valves are connected twenty-six production bores are now in use, and a across each back-pressure set, and a dump condenser further twenty-five or more will probably be in is provided as a flow substitute for an LP condensing service within a year or two. Steam is led from the set. bores through 20" and 30" pipelines to the two power The 30 MW turbines will be of the mixed pressure stations sited on the left bank of the River, type, taking most of their steam at 50 lb/sq in. g some two miles from the centre of the bore field. with additional "pass-in" steam at 1 lb/sq in. g. One of these stations, the "A" building, contains Ultimately if is intended that all the pass-in steam all the smaller (6* and 11 MW ) sets, whereas the shall be derived from flashed hot water, but while "B" building, now under construction, will accom- the quantity of piped hot water is limited it will modate the 30 MW sets. Hot water will at first be be necessary to bypass some of the pass-in steam piped to the station from a group of seven wells from the IP main through a reducing valve. only, situated about half way along the steam pipe Since there is no need to recover the condensate route. from the LP and MP sets, these machines are served The decision to site the power stations close to by jet condensers. The incondensible gases are re- the river bank was taken after first considering the moved from the condensers of the LP sets by means alternative of placing them near the centre of the of high speed multi-stage rotary exhausters and from 1 bore area and serving them with cooling towers. those of the MP sets by means of steam ejectors. The riverside site showed a slight economic advan- Certain design problems are considered in the tage over the bore field site, and this advantage following section. was reinforced by the availability of a far more convenient building area. Design problems A future extension has been tentatively planned for doubling the size of the B station to accommodate THE PROBLEM OF FIXING OPERATING PRESSURES three more 30 MW sets, thus raising the total in- AND TEMPERATURES stalled capacity to 282 MW. If satisfactory experi- The choice of working pressures was partly dictated ence is gained with the hot water plant now under b · force of circumstance. The requirements of the construction, the intention is to generate the greater c]ienlical plant which rvas originally to have formed part of the additional 90 MW from hot water. About one-third of the ultimate output would then be derived from hot water. 1 The following abbreviations have been used in this paper: HP ...... High pressure Figure 2 and tables 1 and 2 show the arrangement, IP...... Intermediate pressure capacities and rated steam consumption of the turbo- LP ...... Low pressure alternators. The use of back-pressure and condensing MP ...... Mixed pressure sets in "cascade" in the A station is the result of TSV . . Turbine stop valve klb/hr . . . . · · · Thousands of pounds per hour in. Hg ...... Conventional inches of mercury * Merz and MeLellan, Consulting Engineers, United Kingdom. CW ...... Cooling water 274 Power development at Wairakei, NZ G14 Armstead 275

M •88• 1 - 41\1: M & 83: . 4,2. %,0 ,- m C.S1 i 5 01%5. i, 944'11,1 2- .036 '1'' i<-4 V ':< .* , zi=- -'- .--111 --- 111• C 1 -&5 -- 0 /\ 0 i. 91'./ J - •M 0 ( .* e FJ '.... •f»-11 »i 0:ow.,04 = ) 5 ia 3 6' i . --*-0- pb 4 m »» 1 = g -t F » 61 4 -•0.3 3g 14 j nfo 21 +E 1.-,-1 -f»• ---ZE " S 4,4 ix 'C« C, 0 ,S ,* •22 i 2, 5 = 07/ : /-- c ./i 1 5: 1 .,4 , 1 1( f 3 .W I *

Table 1. Installed generator capacities

In the A station ' In the. B station Total Turbo-alternators 'TSV *yesswe (MW) (MW) (MW)

13 HP Sets . 180 lb/sq in.g 2 X 6.5 2 X 11.15 22.3 22.3 IP sets 50 lb/sq in.g 2 X 11.15 44.6 LP sets . 0.5 lb/sq in.g 4 X 11.15 ( 1*-in.Hg back-pressure) 90 MP sets 50 and 0.5 lb/sq in.g 3 x 30 ( 1 *-in.Hg back-pressure) 192.2 Authorized plant . . . , 102.2 90 Possible future extension : 90 MP sets ..'.. 50 and 0.5 lb/sq in.g 3 X 30 ( 1*-in,Hg back-pressure) 282.2 Planned ultimate development 102,2 180

part of the project defined two pressure systems and when'that plant was cancelled it was convenient within the plant area, namely 50 lb/sq in. g and to install two IP back pressure sets in its place, each 1 lb/sq in. g, but it was necessary to fix a suitable of about. 11 MW rating, thus enabling the same size admission pressure to the topping sets. Economy of of alternator to be used as with the LP sets. design of these sets · and of the steam pipelines For the extensions there was greater freedom of favoured the choice of a relatively high admission choicein sizing the generators since the chemical plant pressure ; optimum 'yield of wells favoured a lower was no longer a factor to be considered. For the choice. The value chosen was 180 lb/sq in. g. additional HP sets there were advantages in fixing The established IP and LP mains in the power the size either at 6* or at 11. MW to enable the first stations are ·at pressures which are entirely suitable stage alternators to be repeated. Expectations of HP for sequential flashing of hot water. steam winnings were such as to justify a choice of the larger size. The Wairakei bores fall into two classes: those of better quality, the HI? bores, being suitable for Whilst 62* MW and 11 MW sets were regarded as supplying the topping sets, and those of secohdary acceptable sizes for the small pioneering installation quality, the IP botes, being suitable for feeding of 69 MW total, sets of larger size were obviously directly into the IP main at the power stations (see desirable when ,it was decided to extend the plant to a much greater total capacity. It was no longer figure 2). necessary to expand IP steam to vacuum in 'two Investigation showed that the use of fuel fired sets of turbines; with suitable provision for water superheaters could not, be economically justified. separation part way along the turbine it was possible Saturation temperatures therefore prevail throughout to do this in a single machine. All the turbines • the system. in the A station run at 3 000 rpm but by adopting a speed of 1 500 rpm and making use of the greater THE PROBLEM OF SIZING THE GENERATORS pressure range, it was possible to design 30 MW sets As with working pressures, the cancelled chemical with single exhausts. The adoption of twin exhausts plant exercised a considerable influence upon the would have enabled 60 MW sets to be usedbut this choice of generators for the first stage (69 MW ) of size was considered inconveniently large. The pro- development. The specified yield of LP vapour from portions of IP admission steam to LP pass-in steam this plant limited the total power that could be have been fixed by ultimate expectations of the extracted from,it, and the size of each LP condensing quantity of LP flash steam availability. set was in turn limited by the .necessity for fixing One of the 11 MW HP sets and one of the 30 MW an upper limit to the blade tip speed.2 These con- sets will normally serve as spare units. The firm station siderations led to the adoption· of LP sets rated at capacity will therefore be 151 MW. 11.15 MW each. The size of the two smaller HP sets was fixed Table 2. Rated steam consumption of turbines by the required intake of IP steam into the, chemical plant less the early expectations of IP bore steam. Class MW Steam kiblhr The . difference had to be supplied from exhaust steam from the HP sets, and an arrangement of two HP. 6.5 319 569 6* MW sets was convenient. - HP. 11.15 11.15 460 The equivalent power potential of the steam IP ; LP. 11.15 287 consumed by the chemical plant was about 22 MW, MP. 30.0 400 IP 100 LP 2 See section on the problem of corrosion, below. Power development at Wairakei, NZ G/4 Armstead 277 -KEY- B' STAT ION F----7-->r----7-, -C• BACK PRESSURE SET »--r. 1 L--- -Ei-%32036-1 '1 1 <• L. P. CONDENSING SET L ,=9__2

THE PROBLEM OF WATER SEPARATI6N the inner wall after the bend. About 85 to 90 per cent The bore fluid contaills water in quantities ranging of the water is removed in this manner,. the remain- from 4 to 8 times the quantity of steam by weight. ing 10 to 15 per cent being removed in a. "cyclone". This water must be separated from the steam at each With the alternative arrangement the U-bend is wellhead so that the steam fed to the turbines may dispensed with and the whole process of separation be as dry as possible, not only because the presence takes place in a single cyclone with corresponding of water in turbines is harmful.per se but because of simplification. the corrosive constituents in the water phase (see A secondary problem is the removal of the water table 3). Two systems are in use at Wairakei, as after separation from the steam at the wellheads. At illustrated diagrammatically in figure 3. In one, wells where the water is to be used for power genera- crude separation is first effected in an inverted U- tion, the water will be collected in a suitable tank bend placed immediately above the bore. Most of whence it will be pumped to the station. At other the water is thrown against the outer wall of the wells the water must be discarded to waste. To bend and the partially dried steam is led away from avoid costly iloat-operated valves and similar de- 278 II.A.2 Harnessing geothermal energy - Electricity production Table 3. Typical analyses of impurities in geothermal fluids (partsGasPeycontentmillion0/bysteamweight) (partsSole•btes*m millionin hotbywaterweight) HP bore IP bore 4 857 3 467 Bicarbonate (as HCOB) · · 39 C02 132 70 Metaboric acid (H,B204) · 116 H2S 1 1 Fluoride (as F) .... 10 H2 · 5 Chloride (as Cl) . ... 2 318 CH4 3 Sulphate (as S04) ... 34 32 7 17 300 TOTAL 5 000 3 560 PH...... Silica (Si02) · · · · · · · 8.6 Pressure corrected to . 200 lb/sq in.g 70 lb/sq in.g vices, advantage has been taken of the self-regulating Separators are ·incorporated in the station pipe- characteristics of suitably shaped orifices when work to remove most of the exhaust wetness from discharging boiling water. It is found that such ori- the back-pressure turbines. In the 30 MW sets an fices canpass a wide range of flows (about 2* : 1 ratio) integral separator is built into the turbine easing without flooding on the one hand or loss of seal on to remove most of the moisture from the expanding the other. IP steam just before it is mixed with the LP pass-in Lest wet steam should pass out from the well-head stearn. equipment despite the measures taken to remove THE PROBLEM OF CORROSION the water, a ball float valve is fitted in each steam take-off pipe. The presence of gross quantities of The chemical impurities present in the natura] water will lift the ball and isolate the well from the steam and hot water (see table 3) call for special care steam mains. If this should occur the pressure in the in selecting materials. Field tests on material samples cyclone would tend to rise to the "shut-in" pressure were therefore initiated in 1950, the results of which of the well. To protect the equipment from this a gave valuable guidance in this problem. bursting disc is provided which will rupture under Fortunately mild steel shows good resistance to high pressure, enabling the bore to discharge to geothermal fluids so long as no oxygen is present waste. and can safely be used for wellhead gear, steam and Although the steam leaves the wellhead equipment hot water pipes, flash vessels, etc. Copper and nearly dry, some condensation occurs in transit, copper-based alloys, however (other than certain most of which is removed by means of traps placed brasses), proved to be vulnerable, and this precludes at frequent intervals along the pipelines. By repeated the use of brazing spelter. dilution and partial removal the water phase becomes Thirteen per cent chromium iron of the type highly purified by the time the steam reaches the normally used for turbine blades is, in the hardened turbines. state, susceptible to stress-corrosion cracking in the SAFETY VALVES t1f CYCLONE SEPARATOR SAFETY VALVES Uf= STEAM TO STATION .-i COLLECTION -BURSTING , Ttt • (- CYCLONE r TANK 1 DISC 1 STEAM TO STATION SEPARATOR F'l BALL FLOAT -1•-»1-7 1•} BALL FLOAT 9 VALVE , •- v 1 • •' VALVE COLLECTION TANK ------«|---7-BU•|lt'NG WATERORIFICEDISCHARGE ,lvi . TO WASTE WATER DISCHARGE . ORIFICE BORE a. ARRANGEMENT WITH U-BEND b. ALTERNATIVE ARRANGEMENT WITHOUT U-BEND BORE •TOP OUTLET CYCLONE• •BOTTOM OUTLET CYCLONE• Figure 3, Diagram of wellhead equipment Power development at Wairakei, NZ G/4 Armstead 279 presence of geothermal steam, but enjoys immunity The scheme adopted is illustrated in figure 4, in the soft (non-martensitic) state, provided that which shows only one of several HP wells and only sodium chloride is absent, or present only in minute one,IP well. The hot water from each well is collected qflantities. Turbine blades have therefore been made in a vessel whence it is pumped directly into the hot of stainless iron in the soft state. water pipeline. At the upper end of this pipeline is Soft blades, however, are susceptible to erosion connected a "head tank", the purposes of which are in the "wet" end of a turbine, and it is not possible .to stabilise the delivery head of the wellhead pumps, to protect them by brazing on erosion shields owing to give storage capacity to absorb transient changes to the risks of local hardening and the vulnerability of flow, and to provide an actuating water level for of spelter. It was therefore decided to restrict the controlling by means of signals the rate at which the blade tip speeds to the conservative figure of 900 ft• hot water is admitted into the flash vessels at the station. The water level in this tank is about 30 ft sec, although this imposes a limit to the capacity of the condensing sets. above the pipeline, and the space in the upper part of it is vented to the steam supply system so that Sodium chloride is not expected to reach the the pressure at the water surface is approxirnately turbines with the direct bore steam in more than the same as that at which the water is collected negligible quantities, and to intercept the salt at the HP wells. The HP well pumps have a lift carryover from the flash vessels, scrubbers have been of 40 ft, which is sufficient to overcome the static installed to wash the flash steam and so to preserve head of the head tank plus pipe friction in the branch the immunity of the blade material to stress corrosion lines. The IP well pumps have a lift of 450 ft so as cracking. to carry the additional burden of the pressure differ- The most arduous conilitions frorn the corrosion ence between the HP and IP systems. Both types aspect occur in the condensers and gas-exhausting of pump are electrically driven and areof the self- equipment where bore gas, air and moisture are all throttling extraction type. present simultaneously. The internal surfaces of the On arrival at the station the hot water divides main jet condensers and ejector condensers are into two parallel circuits in each of which it passes therefore protected with various resinous coatings. through an automatic control valve which lets down The first stage of each exhauster rotor, where the the pressure to that of the IP flash vessels. The rate' gases are liable to be wet, is of austenitic stainless of movement of these valves is restricted to ensure steel, though subsequent stages, where the gases that surge heads are kept within safe limits. High are normally dry, are of carbon steel. The inter- negative surge heads are particularly dangerous cooler tubes are of pure aluminium - a metal which since they could lead to boiling in the pipeline. is generally resistive to geothermal steam except at high temperatures. The flash vessels are of the cyclone type, similar to, but larger than, the bottom outlet separators used at the wellheads. Suitable erosion shields are THE PROBLEM OF HOT WATER TRANSMISSION provided where the explosive impact of the fiashing water is greatest. The first stage flash steam is led The hot water collected at the wellheads is at · into the IP steam main after passing through a scrub- the boiling temperature corresponding to the pressure. ber. The residual water from the IP flash vessels is If at any point during its transmission to the station passed on through control orifices into the LP the hydraulic pressure is allowed to fall below the flash vessels, and the second stage flash steam, vapour pressure, steam will form in the pipes and after being scrubbed, is led into the LP steam main. this could give rise to unpredictable and possibly The residual water from the LP flash vessels is disastrous water-hammer phenomena. It is not automatically discharged into the river. possible for the hot water to be transmitted freely by gravity from the bores to the station because THE PROBLEM OF CONTROL the gain in hydraulic pressure due to the natural fall of the ground is insufficient to offset the accumulated With the complex system of four different types friction head plus the negative surge heads that may of turbine operating in series and in parallel, and be induced under transient conditions. , with bore steam and Rash steam entering the station at different pressures, it is essential that pressures This difficulty is being overcome by pumping the water so as to raise its hydraulic pressure. As a be so controlled as to ensure a minimum of distur- bance under ' conditions of load variation or plant further precaution the hot water from the HP bores failure. Unless suitable precautions are taken, the will be attemperated by injecting some of the water from the IP bores, which will be about 70°F cooler, change in demand for steam occasioned by such conditions will tend to result in marked variations in order to lower the vapour pressure. The gain obtainable from attemperation is very marked, in the steam pressures in the pipelines and at the the addition of only 10 per cent IP water is equivalent wells by reason of the pressure/flow characteristics of the bores. to a gain in hydraulic head of more than 40 ft, and this gain enables a higher water velocity to be used On the HP system excessive pressure rise under which raises the capacity of the pipeline by 75 per conditions of reduced flow to the station is prevented cent in flow and about 70 per cent in power potential. by, means of automatic vent valves which discharge 10 .M 0

<-I H.T --. I. FW 111 1 W 3- -/5 <2 ./. W>M 6. .... / \ =(D / /\\\ 7'91' H. P. STEAM MAIN /- \* GO,S. /./ (IO• HC - / \\ (D HLR v _L .,cv - j , w."#r•• •,•1Jc.r../.'[i•]- l Her WATER MA,Y /\C:\.1AIH\I \\\\ r---P.I. i• e«• 7. /// //////// s V////// S5 AX•////////// #$3•, \\ I.S. L.S. (-D 3 XY 3 '.= IttL-\- - \ M(¤D llllll 1111111 e<0 -0.- 0#6 ---F ' '<00042 H.P. WELL /.R WELL 44 /FV CO61 4FV KEY:- v 17'•80RE : CV DT H,CW.----_-_Hi•h pressupe collection vessel 1////////,/A F I.C.V...... Intermediate pressure collection vessel. I.M H.T...... Head tank 1F.V...... ln•eptnelia• pressure fiek vessel. Steam connections- 1111111 Ill /1I.E SV.---....- Motor opeiated spill valve. L.FK...._.low ppessui Flash vessel. Hot water connections 10 L..- -- Level detector. /.5...... /P. sc/066ei -- Ejec•rical connecHons /-Ihe w-bon,ment • control valve, 0M S...... floutmete. L.S.-...... L.2 scpubl,ep Ca H.L.R_... Hi9h level,elief DI_..--...Prain tank. - < flash vessels and scrubb•,s 18 a 5_...... Shainev 1;...... ·--12 ,u/6'ne. duplicated, the 2 sets of equipmenF 0 X...... ExhacHion pump. 5...... L.R 1-u•Eine. '.-wotkinl in pa,at/el. = C CompufF CO...... -.Cont,4 OAF,ce C V..__-.Motor op.rated conhol -valve. Figure 4. Diagram of hot water transmission system Power development at Wairakei, NZ G /4 Armstead 281

Table 4. Estimated capital costs of 192 MW authorised installation

Capital cost, Item (thousands) Cost per kilowalt instand

.Heat supply: Prospecting ...... £411 £2.14 Drilling ...... £1 731 69.01 Steam and hot water collection and -trans- mission ..,...·...... £4457 £23.20 £6599 £34.35 Power house and. plant: Civil works and building. . 62 410 £12.54 Turbo-alternators .... £3873 £20,14 Electrical plant and cabling . £408 £2.12 Sundry' 'plapt ...... £542 £2,82 £7233 £37.62 CW system : Civil works and 'building. £854 £4.44 Plant...... £349 21.81 £1203 £6,25 High voltage substation: Civil works and building . £188 £0.98 Plant...... £586 £3.05 £774 64.03 TOTAL f15809 £82.25

NOTE: These costs include import duty and sales tax (where applicable) and the cost of engineering, but they exclude interest during construction. The cost of 220 kV transmission lines is excluded, but the whole of the 11/220 kV transformation and switching substation is included.

to waste such quantities of connected steam 'that control system has been devised which will ensure the station cannot "swallow". The connection of at thai the whole of this quantity is normally delivered least one surplus bore over and above the full load to the, flash.vessels. This will be effected by comparing requirements of the station ensures that the pressure two signals : one from the water level in the head should never fall below the rated. HP turbine admis- tank and one from a flowmeter in the hot, water sion pressure. pipeline at the station end. Any difference between these signals will cause the control valves to open On the IP system the pressure will be maintained or close until the two signals correspond. A rise in the constant only if the total inllow from the IP wells, water level in the head tank, signifying a momentary the HP turbine exhausts, the first stage flash, and excess of infiow over outflow, will, cause the control the HP/IP reducing valves is equal to the total valves to open wider; a fall will cause them to close outflow-through the IP and MP sets and through further. In this manner the balance will be restored. IP/LP reducing valves. Any disturbance in this The size of the head tank has been so chosen as to balance will be reflected ·in a ·rise or fall of pressure absorb transient differences between inflow and in the IP pipework at the station. The IP system outflow and to ensure that the.rate of movementof the is therefore also provided with an' automatic vent control valves will not induce excessive surge heads. valve which adjusts the balance by blowing more or less steam to waste when the pressure starts to A further control element is necessary to cover rise or fail, respectively, the possible loss of attemperating water, which loss would have the effect of reducing the transmission On the LP system a balance between inflow ·and capacity of the hot water pipeline. A, flowmeter will outflow, and therefore constancy of pressure, will therefore be provided to measure the total quantity later 'be ensured by automatically adjusting an of attemperating water, and if this should be less amount of' "spill" from the hot water system, thus than a certain safe value the quantity of HP water affording a means of trimming the quantity of LP will automatically be trimmed to a safe value, by flash steam to the demands of the LP system. For tripping off some of the HP well pumps if necessary. the present, the pressure is normally kept constant In this manner, all the available hot water will by suitably adjusting the governors of 'the IP and normally be delivered to the flash vessels » unless LP sets. some curtailment is necessitated by an insufficiency The characteristics of the hot water extraction of attemperating water. If the turbines cannot absorb pumps at the wellheads will. normally ensure 'the the whole of the flash steam from the transmitted delivery into the pipeline of whatever quantity water then some spilling of hot water will be neces- , of hot water is yielded by the selected. wells. A. sary, as noted above. 282 II.A.2 Harnessing geothermal energy - Electricity production

Costs Conclusion

The estimated capital costs of the 192 MW author- The advent of geothermal power in New Zealand's ised installation are set out in table 4. If the installa- North Island has altered the pattern of generation. tio'n is ultimately extended to 282 MW it is hoped that Until recently almost the whole of the load was the capital costs per kilowatt installed will fall to carried by hydro stations, each of which operated less than £78. at a load factor of about 58 per cent, which was that of the system load. Wairakei is now providing a The production costs per kWh generated will of growing base load at a high-load, factor and this course depend on the station output. It is hoped that with 192 MW installed it will be possible to generate has to be supplemented by some low-load factor stations. Theinstalled capacity of some of the hydro- about 1 220 million kWh per annum. The greater stations has therefore been increased to allow for part of the production costs will consist of capital charges, and these will in turn partly depend. uppn this, and a new 180 MW coal-fired thermal station at is availible for carrying peak loads. the life assigned. to the assets. Owing to the uncertain- By the time that the authorised installation of ties attached to the endurance of, the thermal field 192 MW has been wholly commissioned it is expected itself, it 'has been deemed advisable to assume that Wairakei will be contributing about one-1 an average life of only twenty years for all the quarter of North Island's power requirements. assets. On this basis, and reckoning interest at 5 per cent per annum, the average cost per unit when Experience is steadily being gained in the manage- the stations are in full production is expected to ment of the thermal field and in the operation of the be under 0.4 pence per. kWh. If the installation bores and plant. The turbines run very steadily. is ever extended to 282 MW it is expected that It' seems probable that geothermal power will play the production costs per unit will fall by about an increasingly prominent part in the economic life 12 per cent. of New Zealand.

Summary

This paper relates to one particular geothermal extensive exploitation of the hot water is eventually development - namely, the scheme for generating made. electric power at Wairakei in North Island, New After a short description of the steam field, the Zealand. Whereas. other papers presented at this power station site and the plant, the paper passes Conference are concerned with the winning of steam on to a brief consideration of six specific problems and hot water from below ground, this paper describes of design. These are: (a) the factors which determined how these fluids are utilised at Wairakei for the - the workipg pressures and temperatures; (b) the production of power. The broad engineering features considerations which fixed the sizes of the turbo- of the installation are briefly described and some of alternators; (c) the problem of separating the steam . the principal design problems are mentioned. Esti- at the wellheads from the far larger quantities of mates of capital expenditure and of production costs hot water associated with. it, the disposal of the are also given. hot water, and the maintenance of i high dryness Wairakei. has already been contributing about fraction while the steam is in transit to the station 10 per cent of North Island's power requirements, and expanding through the turbines; (d) the avoid- and by the end of 1962 or early 1963 it is hoped that ance of corrosion; (e) the problem of transmitting this contribution may perhaps be as ·much as 20 per large quantities of hot water over. a long distance cent. The New Zealand Government has authorized without the occurrence of boiling in the pipes; and an installation of 192 MW of plant, of which the first lastly (f) the establishment of a system of controls which enables steam pressures at the station to be stage (69 MW ) was completed in .March 1960. Tenta- tive planshave been prepared for later extefiding maintained as nearly constant as possible so that the scheme to a. total installed capacity' of 282 MW. the generators may run smoothly and at steady It is intended that about one-third of the ultimate output, and which ensures that all the available output will be derived from the hot water and two- hot water is delivered to the station, consistent thirds from the steam yielded by the bores. Mean- with the ability of the turbines to swallow the flash while, since· the proposed techniques for transmitting steam derived therefrom, without rapid fluctuations and flashing hot water in very great quantities are of flow. as yet largely untried, a relatively small-scale develop- The estimated capital outlay of the authorised ment,'using only a fraction of the hot water, is now Wairakei scheme is equivalent to about £82.25 per under construction as part of the 192 MW authorized kilowatt installed. If the installation is ultimately installation. Experience gained from this restricted extended to 282 MW it is expected that the capital development should be of great value if a more outlay per kilowatt installed will fall below £78.. Power development at Wairakei, NZ G/4 Armstead 283

Production costs have been estimated at under installed in existing hydroelectric stations and by a 0.4 pence per kWh when the 192 MW installation is in recently constructed coal-fired station at Meremere. full production; if the installation is ever extended to In a short paper the description of a complex 282 MW these costs should 'fall by about 12 per cent. installation must of necessity be brief and confined The •Wairakei scheme is essentially for the pro- to the main features only. Likewise it is not possible duction of base load energy at high load factor. to make more than very short reference to only Peak loads will be carried by additional generators some of the many design problems involved.

LA CENTRALE D'ENERGIE GEOTHERMIQUE DE WAIRAKEI, NOUVELLE-ZELANDE

Resumi

On s'en tiendra, dans la prasente communication, le besoin, A la bouche des puits, de s6parer la vapeur A une seule centrale gdothermique, celle qui est des quantitds beaucoup plus considdrables d'eau destinde h. la production de courant dlectrique A chaude qui viennent avec elle, par la manidre de Wairakei, ile du Nord, Nouvelle-Ztlande. Tandis disposer de l'eau chaude et par le moyen de maintenir que d'autres mdmoires soumis A cette m6me conf6- un degrd de sacheresse trds dlevd pendant que la rence s'attachent A la rdcupdration de 'vapeur et vapeur s'achemine vers la centrale et:se ddtend dans d'eau chaude du sous-sol, celui-ci ddcrit leur utilisa- les turbines, d) la lutte contre la corrosion, e) . le tion, h Wairakei, A la production d'dnergie dlectrique. probldme pos254par le besoin de transporter de grosses Les principales caractdristiques techniquesde l'instal- quantit6s d'eau chaude sur de grandes distances lation font l'objet d'une brdve description, et on sans qu'il se produise d'dbullition dans les conduites signale quelques-uns des principaux probl&mes qu'en et, finalement, f) la mise au point d'un systhme de soullve la'rdalisation. commandes permettant de maintenir les pressions Wairakei assure ddjEM la couverture de 10 p. 100 de vapeur aussi constantes que possible A la centrale, environ des besoins dnergdtiques de l'ile du Nord de maniere a ce que les alternateurs fonctionnent et, pour la fin de 1962 ou le ddbut de 1963, on espdre sans A-coups et. A d6bit soutenu, pour assurer que que la fraction • ainsi fournie atteindra jusqu'a toute la quantitd d'eau chaude compatible avec la 20 p. 100. Le Gouvernement ndo-zdlandais a autorisd capacita, de la part des turbines, a absorber la vapeur l'installation de 192 mdgawatts, programlne dont rapidement produite, est bien fournie a la centrale la premidre tranche (69 magawatts) atait pr6te en sans rapides fluctuations de ddbit. mars 1960. On a prdpard certains plans prdliminaires Les· investissements de capitaux ndcessaires pour pour passer ultdrieurement A une capacitd installde mener A bien le prgjet de Wairakei tel qu'il est totale de 282 mdgawatts. On se propose d'utiliser actuellement autonse correspondent A 82,25 livres l'eau chaude pour la production d'environ 30 p. 100 environ par kW insta116. Sil'on finit par amdnager les de 1'6nergie envisagde, en fin de compte, la vapeur 282 mdgawatts prdvus, il faut. s'attendre h voir les ddbitde par les puits devant en foul'nir les deux tiers. frais de premier 6tablissement par kW installd Entre-temps, pour. autant que les techniques de tomber & moins de 78 livres. Les frais de production transport et de vaporisation rapid254de l'eau chaude sont dvaluds A moins de 0,4 penny par kWh pour en quantitds trds importantes Il'ont pour ainsi dire l'installation de 192 mdgawatts en plein fonction- pas encore 6td mises A 1'6preuve, on construit actuel- nement. Si l'on arrive au 282 mdgawatts, ces frais lementune installation A dchelle relativement modeste seraient raduits de 12 p. 100 environ. et n'utilisant qu'une partie de l'eau chaude disponible, dans le cadre du programme d'ensemble qui autorise Le projet de Wairakei envisage essentiellement la l'amdnagement de 192 mdgawatts. L'expdrience production d'dnergie avec charge de base et un acquise avec ce projet limit6 ne saurait manquer facteur de charge dleve. Les pointes de charge seraient •. de prdsenter beaucoup de valeur si' on en venait, en couvertes par des gdndrateurs supplamentaires a fin de compte, h mettre l'eau chaude en exploitation installer aux centrales hydro-dlectriques en. fonction- sur une PJus grande 6chelle. nement, ainsi qu'A une autre, rdcemment dtablie, chauffde au charbon et situde A Meremere. Aprds une brdve description du champ producteur de vapeur, du site. de la station"et de la centrale, La description d'une installation complexe doit l'auteur passe rapidement en revue six probldmes ndcessairement se limiter A celle des principales particuliers de rdalisation. Ce' sont : a) les· 616ments caracteristiques, quand il s'agit d'un mdmoire aussi qui ont ddtermind les pressions et les tempdratures bref que celui-ci. De meme, on ne peut que trls de travail, b) les considdratiofts qui ont dictd la taille succinctement passer en revue certains des nombreux des turbo-alternateurs, c) la question soulev6e par probl&mes qu'en souldve la rdalisation.