(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (19) World Intellectual Property Organization International Bureau (43) International Publication Date (10) International Publication Number 5 August 2010 (05.08.2010) WO 2010/086009 Al (51) International Patent Classification: (81) Designated States (unless otherwise indicated, for every F04D 17/12 (2006.01) F04D 27/02 (2006.01) kind of national protection available): AE, AG, AL, AM, F04D 25/06 (2006.01) F04D 29/58 (2006.01) AO, AT, AU, AZ, BA, BB, BG, BH, BR, BW, BY, BZ, CA, CH, CL, CN, CO, CR, CU, CZ, DE, DK, DM, DO, (21) International Application Number: DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT, PCT/EP2009/009284 HN, HR, HU, ID, IL, IN, IS, JP, KE, KG, KM, KN, KP, (22) International Filing Date: KR, KZ, LA, LC, LK, LR, LS, LT, LU, LY, MA, MD, 23 December 2009 (23.12.2009) ME, MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI, (25) Filing Language: English NO, NZ, OM, PE, PG, PH, PL, PT, RO, RS, RU, SC, SD, SE, SG, SK, SL, SM, ST, SV, SY, TJ, TM, TN, TR, TT, (26) Publication Language: English TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW. (30) Priority Data: (84) Designated States (unless otherwise indicated, for every 0901 576.9 30 January 2009 (30.01.2009) GB kind of regional protection available): ARIPO (BW, GH, GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM, (71) Applicant (for all designated States except US): GARD ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ, NER DENVER DEUTSCHLAND GMBH [DE/DE]; TM), European (AT, BE, BG, CH, CY, CZ, DE, DK, EE, Industriestrasse 26, 9761 6 Bad Neustadt (DE). ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU, LV, (72) Inventor; and (75) Inventor/Applicant (for US only): PEUSSA, Jouko, Tapani [FIZDE]; Badeallee 4, 55543 Bad Kreuznach (DE). MC, MK, MT, NL, NO, PL, PT, RO, SE, SI, SK, SM, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW, ML, MR, NE, SN, TD, TG). Published: (74) Agents: BUCKS, Teresa, Anne et al; Bould Wade Ten- with international search report (Art. 21(3)) nant, Verulam Gardens, 70 Gray's Inn Road, London with information concerning incorporation by reference WClX 8BT (GB). of missing parts and/or elements (Rule 20.6) (54) Title: IMPROVEMENTS IN MULTI-STAGE CENTRIFUGAL COMPRESSORS (57) Abstract: The invention relates to an improved multi-stage centrifugal compressor (10) comprising at least four centrifugal compression stages ( 11,12,13,14), each including an impeller. The im pellers of one pair of the stages (12,13) are mounted on a first shaft (23) coupled to a first high speed di rect drive motor (16), and the impellers of another pair of the stages ( 11,14) are mounted on a second shaft (24) coupled to a second high speed direct drive motor (15). The speed of the first and second motors is controlled by at least one drive (25) such that the impellers are all driven at the same speed. Specific Speed (N ) FIG. 1
IMPROVEMENTS IN MULTI-STAGE CENTRIFUGAL COMPRESSORS The invention relates to improvements in multi-stage centrifugal compressors and, in particular, to an improved multi-stage centrifugal compressor. Variable speed dynamic compressors, such as centrifugal compressors, have been used to compress air, or other gases, since the 1960s. Centrifugal compressors, which comprise a cylindrical assembly o f compressor blades mounted to an axis to form the impeller, are used in a wide variety o f fields for a number o f reasons. They are generally energy efficient, are low maintenance as they have few moving parts, and they usually give a higher air flow than a similarly sized reciprocating compressor. The main disadvantage o f centrifugal compressors is that they generally cannot achieve the high compression ratios o f reciprocating compressors without multiple stages, although multi-stage centrifugal compressors can achieve significant discharge pressures. The performance o f a centrifugal compressor is expressed in terms o f impeller speed, total head and required volumetric flow. In centrifugal compressors the pressure ratio, which is the ratio o f the air pressure exiting the compressor to the air pressure entering the compressor, is proportional to the impeller speed. The stage efficiency correlates with the specific speed which is defined as the speed o f an ideal compressor geometrically similar to the actual compressor which, when running at this speed will raise a unit o f volume, in a unit of time through
a unit o f head. Specific speed (N )can be calculated from the following formula : - N 3 = N *VQ H 0-75 wherein: N = the rotational speed o f the impeller (rpm) Q = the volumetric flow (1/m) H = the total dynamic head (m) Figure 1 shows a plot o f efficiency against specific speed for a range o f centrifugal compressors indicating that there is an optimum specific speed, with efficiency falling off at high and low specific speeds. Prior art centrifugal compressors used in industrial air applications are typically two or three stage compressors. In order to achieve the required pressure ratio, the overall efficiency can be improved with intercooling between the stages since the specific work (w), i.e. the work per unit mass flow per stage can be calculated by the following formula: - w = Ri*T * ( n_) * (Pr (n"1)/n -l) (n-1) wherein: R i = specific heat o f the gas at a constant pressure (J/kg.K) T 1 = inlet temperature (K)
n = the ratio o f the specific heat of the gas at the constant pressure and the specific heat of the gas at a constant volume Pr = pressure ratio Ignoring small changes in the specific heat (R 1 ), it can be shown that the overall specific work (w) is smaller for compression in two stages with cooling back to near to the inlet temperature (Ti) at the second stage inlet, than for compression in a single stage. Similarly, the specific work (w) for three stage compression with intercooling is smaller than for two stage compression. A s air or gas is compressed in each stage, the volumetric flow (Q) will reduce in proportion to the stage pressure ratio (Pr). If the head rise is split evenly across the stages, then the specific speed (N s2 ) o f the second stage will be smaller than the specific speed (N s ) o f the first stage. Similarly, the specific speed o f the third stage (N 3 ) will be smaller than the specific speed (N 2 ) of the second stage. Typically, the second stage specific speed (N 32 ) will be in the range of high stage efficiencies as the range o f specific speeds with good efficiency is sufficiently broad in this range of compressors. It is possible that the efficiency o f the third stage is less than optimum if the specific speed is sufficiently low (see Figure 1 ). Prior art three stage centrifugal compressors often have the first and second stage impellers on one shaft and the third stage impeller on a second shaft. A gearbox is arranged to drive each shaft at, or near, the optimum speed.
An example of such an arrangement is described in US-B- 6488467. More recently, however, direct drives have been employed in centrifugal compressors, for example a s described in EP-A-1319132 and EP-A-1217219. Gearboxes are not used in direct drive compressors and so the speed o f each stage can be optimised by using individual motors and drives a s shown, for example, in US-A-20070189905. The disadvantage o f such systems is that individual motors and drives are expensive and require complex control systems to control the multiple motors/drives. It is therefore an object o f the present invention to provide an improved multi-stage compressor which has an improved efficiency. The invention therefore comprises a multi-stage compression system comprising at least four centrifugal compression stages, each including an impeller, in which the impellers o f one pair o f the stages are mounted on a first shaft coupled to a first high speed direct drive motor, and the impellers o f another pair o f the stages are mounted on a second shaft coupled to a second high speed direct drive motor, the speed o f the first and second motors being controlled by at least one drive such that the impellers are all driven at the same speed. This arrangement has the advantage that the compression system can be simplified in terms o f number o f drives without compromising on stage efficiencies.
The invention will now be described, by way o f example only, with reference to the accompanying drawings in which: - Figure 1 is a graph showing the efficiency o f a centrifugal compressor versus specific speed; Figure 2 is a schematic representation o f one embodiment o f the invention; and Figure 3 is a schematic representation o f another embodiment o f the invention. A s shown in Figure 2, a three stage centrifugal compressor 1 0 comprises two first stages 11,12 mounted in parallel to each other, and a second stage 13 and a third stage 14 each connected in series. Thus the fluid to be compressed is split equally across the fluid inlets to the two first stages 11, 1 2 and is compressed simultaneously. The fluid discharged at the fluid outlets o f the two first stages 11,12 is then recombined before passing to the fluid inlet o f the second and then the third stage. The stages 11/12,13,14 are driven by a pair o f direct drive high speed motors 15/16. The four impellers are mounted on two shafts 23,24 which are driven by the two high speed direct drive motors 15,16. The impeller o f the second stage 13 is mounted on the same drive shaft 2 3 a s the impeller o f one o f the first stages 12. The impeller o f the third stage 14 is mounted on the same shaft 24 as impeller o f the other first stage 11. The speed o f the motors 15,16 is controlled by a single variable frequency or other drive or controller 2 5 and hence all four impellers are driven at the same speed. More than
one drive 25 or controller may be utilised in which case all four impellers will still be driven at the same speed. The fluid to be compressed is drawn into the impellers o f the two parallel first stages 11,12. The compressed fluid streams discharged from the two first stages 11,12 are passed through an intercooler 21 and combined before being drawn into the impeller o f the second stage 1 3. The fluid discharged from the second stage 13 is passed through a second intercooler 2 2 before being drawn into the impeller o f the third stage 14. The fluid discharged from the third stage 14 is finally passed through after cooler 26 before being discharged for use. The two first compressed stage fluid streams may be combined before or after passing through the first intercooler (21). This configuration with the splitting o f the first stage 11/12 has the advantage that the cost, complexity and probability o f mal-operation associated with additional drives and motors are all greatly reduced. The efficiency o f each stage 11/12,13,14 can be run near optimum as the specific speed range over the three stages 11/12,13,14 is relatively small. For example, i f the overall pressure ratio (Pr) is 8, and with equal pressure rise across each stage 11/12,13,14, the specific speed (N 31 )o f each of the first stages 11,12 will be proportional to V(Q/2), where Q is the total volumetric flow through the compressor at inlet and each first stage 11,12 compresses 50% o f the flow. The specific speed (N 32 )o f the second stage 13 will be proportional to V
(Q/2) and the specific speed (N S3 )of the third stage 14 will be proportional to (Q/4) 0 5. In an alternative embodiment of the present invention, a fourth stage is added, which enables the compressor 1 0 to achieve higher pressures than the previously described embodiment. A s shown in Figure 3 there is only a single first stage 12 and a third intercooler 27 is located between the third stage 14 and the fourth stage 2 8. The additional intercooler 27 helps to optimise the thermodynamic compression efficiency by maintaining low temperatures at the inlet to the fourth stage 28. In this arrangement, the impellers o f the first and second stages 12,13 are mounted on a first shaft 2 3 and the impellers o f the third and fourth stages 14,28 are mounted on the second shaft 24. A s before, each shaft 23,24 is driven by a high speed direct drive motor 15,16 and the motors 15,16 are controlled by one or more drives 25.
CLAIMS : 1. A multi-stage compression system comprising at least four centrifugal compression stages, each including an impeller, in which the impellers o f one pair o f the stages are mounted on a first shaft coupled to a first high speed direct drive motor, and the impellers o f another pair o f the stages are mounted on a second shaft coupled to a second high speed direct drive motor, the speed o f the first and second motors being controlled by at least one drive such that the impellers are all driven at the same speed. 2. A multi-stage compression system as claimed in claim 1 wherein a pair o f first compression stages are mounted in parallel to each other, and a second and a third compression stage are mounted in series with the pair o f first stages. 3. A multi-stage compression system as claimed in claim 2 in which the impeller o f one o f the first stages and the impeller o f the second stage are mounted on the first shaft and the impeller o f the second of the first stages and the impeller o f the third stage are mounted on the second shaft. 4. A multi-stage compression system as claimed in claim 1 wherein a first, second, third and fourth compression stage are mounted in series. 5. A multi-stage compression system as claimed in claim 4 impeller o f the first stage and the impeller o f the second stage are mounted on a first shaft and the impeller of the third stage and the impeller o f the fourth stage are mounted on the second shaft.
6. A multi-stage compression system a s claimed in any one of the preceding claims in which a first intercooler is connected to a fluid outlet o f the first compression stage (s) and the fluid inlet of the second compression stage. 7. A multi-stage compression system a s claimed in claim 6 as dependent on claim 2 in which the first intercooler is connected to a fluid outlet o f each o f the first compression stage (s) such that fluid streams received from each o f the two first compression stages are combined to provide a single cooler fluid stream to the second compression stage. 8. A multi-stage compression system as claimed in any one o f the preceding claims in which a second intercooler is connected to a fluid outlet o f the second compression stage and a fluid inlet o f the third compression stage. 9. A multi-stage compression system as claimed in claim 4 in which a third intercooler is connected to a fluid outlet o f the third compression stage and the fluid inlet of the fourth compression stage. 10. A multi-stage compression system as claimed in any one o f the preceding claims in which an after cooler is connected to a fluid outlet o f the last o f the compression stages. 11. A multi-stage compression system as claimed in any one o f the preceding claims in which the motors are controlled by at least one variable frequency drive.
12. A multi-stage compression system substantially a s hereinbefore described, with reference to and as shown in the accompanying drawings.
INTERNATIONAL SEARCH REPORT A. CLASSIFICATION OF SUBJECT MATTER INV. F04D17/12 F04D25/06 F04D27/02 F04D29/58 International application No PCT/EP2009/009284 According to International Patent Classification (IPC) or to both national classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) F04D Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched Electronic data base consulted during the international search (name of data base and, where practical, search terms used) EPO-Internal, WPI Data C. DOCUMENTS CONSIDERED TO BE RELEVANT Category * Citation of document, with Indication, where approp πate, ol the relevant passages Relevant to claim No US 2007/189905 A l (DINSDALE BRITTON D [US] 1-11 ET AL) 16 August 2007 (2007-08-16) cited in the application paragraph [0014] paragraph [0025] - paragraph [0038] figures 1-2 EP 1 217 219 A2 (COOPER CAMERON CORP [US]) 1-11 26 June 2002 (2002-06-26) cited in the application paragraph [0012] paragraph [0023] - paragraph [0036] figure 1 WO 2005/068847 A l (CRYOSTAR FRANCE SA 1-11 [FR]; POZIVIL JOSEF [FR]; GERSTENDOERFER HELMUT [CH) 28 July 2005 (2005-07-28) page 5 - page 6 figure 1 Further documents are listed in the continuation of Box C See patent family annex Special catego πes of cited documents "A" document defining the general state of the art which is not considered to be of particular relevance "E' earlier document but published on or after the international filing date "T" later document published after the international filing date or pπoπty date and not in conflict with the application but cited to understand the principle or theory underlying the invention "X" document of particular relevance, the claimed invention cannot be considered novel or cannot be considered to "L" document which may throw doubts on priority claιm(s) or involve an inventive step when the document is taken alone which is cited to establish the publication date of another "Y" document of particular relevance, the claimed invention citation or other special reason (as specified) cannot be considered to involve an inventive step when the "O" document reler πng to an oral disclosure, use, exhibition or document is combined with one or more other such docu other means ments, such combination being obvious to a person skilled "P" document published prior to the international filing date but in the art later than the pnority date claimed "&" document member of the same patent family Date of the actual completion of the international search Date of mailing of the international search report 18 March 2010 31/03/2010 Name and mailing address of the ISA/ Authonzed officer European Patent Office P B 5818 Patentlaan 2 NL - 2280 HV Rljswijk TeI (+31-70) 340-2040, Fax (+31-70) 340-3016 Homan, Peter Form PCT/ISA/210 (second sheet) (April 2005)
INTERNATIONAL SEARCH REPORT International application No PCT/EP2009/009284 Box No. Il Observations where certain claims were found unsearchable (Continuation of item 2 of first sheet) This international search report has not been established in respect of certain claims under Article 17(2)(a) lor the following reasons 1 I Claims Nos because they relate to subject matter not required to be searched by this Authority, namely Claims Nos because they relate to parts of trie international application that do not comply with the prescribed requirements to such an extent that no meaningful international search can be carried out, specifically see FURTHER INFORMATION sheet PCT/ISA/210 Claims Nos because they are dependent claims and are not drafted in accordance with the second and third sentences of Pule 6 4(a) Box No. Ill Observations where unity of invention is lacking (Continuation of item 3 of first sheet) This International Searching Authonty found multiple inventions in this international application, as follows As all required additional search fees were tmely paid by the applicant, this international search report covers all searchable rclaim<s5 2 I I As all searchable claims could be searched without effort iustifying an additional fees, this Authonty did not invite payment of additional fees 3 As only some of the required additional search fees were timely paid by the applicant, this international search report covers ' ' only those claims for which fees were paid, specifically claims Nos 4 I No required additional search fees were timely paid by the applicant Consequently this international search report is restricted to the invention first mentioned in the claims, it is covered by claims Nos Remark on Protest The additional search fees were accompanied by the applicant s protest and, where applicable the 1 ' payment of a protest fee The additonal search fees were accompanied by the applicant's protest but the applicable protest ' ' fee was not paid within the time limit specified in the invitation No protest accompanied the payment of additional search fees Form PCT/ISA/21 0 (continuation of first sheet (2)) (April 2005)
International Application No. PCT/EP2009 /009284 FURTHER INFORMATION CONTINUED FROM POT/ISA/ 2 10 Continuation of Box II. 2 Claims Nos.: 12 At present no opinion can be given for claim 12 because the matter for which protection is sought is not clearly defined. The scope of the wording "substantially as hereinbefore described" is vague and unclear. Additionally, the claims must not, in respect to the technical features of the invention, rely on references to the description or drawings (Guidelines, par. 5.10). The applicant's attention is drawn to the fact that claims relating to inventions in respect of which no international search report has been established need not be the subject of an international preliminary examination (Rule 66.1(e) PCT). The applicant is advised that the EPO policy when acting as an International Preliminary Examining Authority is normally not to carry out a preliminary examination on matter which has not been searched. This is the case irrespective of whether or not the claims are amended following receipt of the search report or during any Chapter I I procedure. If the application proceeds into the regional phase before the EPO, the applicant is reminded that a search may be carried out during examination before the EPO (see EPO Guideline C-VI, 8.2), should the problems which led to the Article 17(2) declaration be overcome.
INTERNATIONAL SEARCH REPORT Information on patent family members International application No PCT/EP2009/009284 Patent document Publication Patent family Publication cited in search report date member(s) date US 2007189905 A l 16-08-2007 NONE EP 1217219 A2 26-06-2002 US 2002076336 A l 20-06-2002 WO 2005068847 A l 28-07-2005 CN 1910370 A 07-02-2007 EP 1706646 A l 04-10-2006 JP 2007518017 T 05-07-2007 US 2008008602 A l 10-01-2008 Form PCT7ISA/21 0 (patent family anπsx) (April 2005)