Steam & Power Forum RSS Welcome to the steam & power forum, a bulletin board dedicated to power & heating plants, boilers, turbines, steam, HTHW, pressure vessels, HRSG, piping and condensate, combustion including ASME questions and more. 6/25/2017 11:38:29 AM Poppy at Steam & Power Forum RSS 64 150 Hrsg - By: John [1794] What would be some safety protections for a hrsg in the gas turbine logic? Fri, 23 Jun 2017 03:24:00 -0300 Coupling alignment - By: John [1794] How are couplings aligned on a large condensing steam turbine? Thu, 22 Jun 2017 00:33:00 -0300 Re: Drum feed water - By: [50] Hullo Jim!<br /><br />Thanks for your comments, due to your experience you can give much more specific data and practical solutions... placing the valve downflow of the economizer will certainly place the pressure fall in the valve after the eco, so it will work at a higher pressure and reduce the possibility of steaming.<br /><br />I had no idea that some steaming is acceptable... steam will be a less efficient cooling medium than water for the economizer tubes, so some overheating of the tubes might be a nasty consequence if there be too much steam, but as you speak of 10 to 15 percent, it must be still safe working conditions.<br /><br />Mr. Tushars problem apparently was different as I had first thought, as I realized after reading his last posting. He has to deal with a low pressure boiler, and feed water temperature may not be so strict a factor in my opinion, specially if for a short period...<br /><br />Regards<br /><br />Claudio Molanes<br /><br /> Tue, 20 Jun 2017 19:36:00 -0300 Re: Drum feed water - By: [50] Oh, Mr. Tushar!<br /><br />From your data I now realize that you are speaking of a low pressure unit, 7,5 barg. In this case I imagine you have an industrial boiler, perhaps obtaining saturated steam for industrial processes as this is quite common. As you mention a drum, it may be a D-type boiler... you speak now of introducing feed-water at 45C, that is, with no preheating. <br /><br />This will impair somewhat the boiling process so you will certainly loose efficiency for your cycle, but I believe will not bring serious consequences unless the feed pipe is too close to the steel walls of the drum. In any case you should have thermocouples to check the temperture differentials.<br /><br />If your needs are to replace or repair an existing economizer, or existing preheaters, then it should be considered as temporary procedure and acceptable, but not in the long run, specially from economic point of view. If you can preheat the water using steam, hot condensates, flashed steam or the like, both the boiler and the purse will be happy.<br /><br />As for your last paragraph, I do not know if I understood properly, with 173C saturation temperature, usual feed water should be, as I spoke of 10 to 15 lower, so in many plants would work at 160 C or so. Feed water at 45 means much lost efficiency.<br /><br />Claudio Molanes<br /><br /><br /><br /><br /><br /><br /><br /> Tue, 20 Jun 2017 19:14:00 -0300 Re: Trip on differential voltage relay - By: Ross Burns [390] Maybe you can tell me what you mean by differential voltage relay? There should be a device number associated with your protection relay in the switchgear room such as 27 for a Undervoltage Relay or 87B for Differential Protection for primary phase fault protection for AC Generator using current transformers. Or a 60 for Voltage balance protection?<br /><br />So maybe you are asking about a device number 87 known as a Differential -Current- Relay protection? The device 87 is a must have on a Gas Turbine Simple Cycle AC Generator. <br /><br />Regardless of the prime mover such as a combustion turbine or gas turbine the AC generators have a level of protection that is consistent to the country, history of facility or power station and age of the installation as well as philosophies. <br /><br />My thoughts are a 87B Differential Relay protection trip is a serious fault and at least a generator main breaker trip will occur. On large stations a backup protection relay can be employed known as a 87U Differential Relay that extends protection to the Generator and Step-up Power Transformer, so with a device like 87U the scheme is to rachet-up to a full generator trip, which includes the excitor or field as well as the generator main breaker, and switchgear trip to protect the power step-up transformer. This means the combustion turbine will overspeed and hopefully just momentarily.<br /><br />Should a device number 87 Differential Relay activate then it will be without time delays and be instantaneous. So, we can see a 87 device is a must have, and on a Gas Turbine Simple Cycle AC Generator a 87U activation will trigger a AC generator trip with the power step-up transformer. <br /><br />In decision is likely to include an orderly manual emergency shutdown on the gas turbine, for the scheme to do so is likely to be carefully weighed against the risk of not having an auto-emergency shutdown on the gas turbine from a 87 generator trip. Either way spinning the combustion turbine or gas turbine with a 87 trip is not productive since a serious electrical fault is present that needs investigation.<br /><br />Perhaps, we can hear from others who have different philosophies from their country on protection relays that result in a gas turbine trip resulting from a 87 activation.<br /><br />Ross Tue, 20 Jun 2017 11:12:00 -0300 Re: Drum feed water - By: Tushar [2153] Mr. Claudio Molanes,<br /><br />I understand what you explained. Thank you for that!<br /><br />My concern is, what will happen if I put condensate return of say 45 Deg. C directly to drum having pressure of 0.75 MPag saturation temp of 173 Deg.C approx.. i.e. higher approach point from usual 10-15 Deg.C <br /><br />Will there be any operational problem?<br /><br />Kindly advice.<br /><br />Regards,<br />Tushar Tue, 20 Jun 2017 01:10:00 -0300 Re: closed feedwater heater - By: Murphy [21] I have hoped you will give a little more information your regenerative or reheat regenerative cycle. It will clarify a lot for me. Because your mentioned a closed high press feedwater heater then I can guess that the type of construction is a shell and tube with the tube side at very high pressure. When in series these are counter flow. I cant understand an air leak on these, but I can understand an air leak in the low pressure feedwater heaters. Maybe your power station has something I have not seen before. Anyhow, can you share with us more info? Mon, 19 Jun 2017 15:32:00 -0300 Re: Drum feed water - By: Jim Watts [764] Ha Ha I just realised I have been typing HSRG instead of HRSG Sun, 18 Jun 2017 02:04:00 -0300 Re: Drum feed water - By: Jim Watts [764] Hi Claudio,<br />I finally decided to comment on your answer even though you have probably realised by now the feed pump is not in the steaming zone and only pumps dearator water at dearator temperature with a static head.<br />The only consideration with economiser steaming is the distribution of flow in the economiser tubes as steaming will reduce flow in some if not all are steaming at the same rate. The pump capacity is able to deal with the small head increase.<br />However if a wide variation is possible as sometimes occurs in HSRG the feedwater control valve is moved to be between the economiser and the steam water drum.<br />This supresses steaming by increasing the economiser saturation temperature slightly. <br /> <br /><br /> Sun, 18 Jun 2017 01:53:00 -0300 Trip on differential voltage relay - By: John [1794] If your gas turbine generator trips on differential voltage relay what would be your course of action to take? Fri, 16 Jun 2017 23:48:00 -0300 Re: Steam turbine efficiency - By: [50] Mr. John:<br /><br />You are probably aware of this, but my first idea is when it is possible to lower the cooling water temperature, thus lowering the exit pressure. On board ships with steam plants was evident even in a fortnight period, as when crossing the equator, with high water temperature and low vacuum, and then, shortly after, steaming in polar waters, water being some 20 C colder, and then the attained vacuum and the efficiency increased. It goes without saying that the air ejectors play an important role in keeping the vacuum.<br /><br />If you were not plant operator, I might add that the conditions of the turbine should be controlled , as eroded bladings, worn out seals or the like, but I am sure you have this under control.<br /><br />These are but basic concepts, I am sure you will receive other ideas of possibilities that I ignore, or that are right now out of my memory.<br /><br />Claudio Molanes<br /><br /><br /><br /> Wed, 14 Jun 2017 19:10:00 -0300 Steam turbine efficiency - By: John [1794] What would be some ways to increase the efficiency of a condensing steam turbine.thank you Wed, 14 Jun 2017 12:04:00 -0300 Re: Drum feed water - By: Jim Watts [764] As has already been stated the feedwater is limited to saturation temperature in the drum because it is impossible to be higher. However steaming in the economiser of conventional fired boilers is not uncommon with some being designed to do so and others occuring due to fouled superheaters or other firing issues. 10 to 15 percent steaming would be the maximum however.<br /><br />It is a different matter in HSRG however as the relative low gas temperatures and low steam and water flows require a higher differential between the gas and steam temperatures to cool the exhaust gas temperature. approach temps are highly optimised even to the extent of running three drum pressures and of course no feed heaters after the dearator.<br /><br />So your answer is its probably impossible to raise on a normal boiler and extremely undesirable on a HSRG. Wed, 14 Jun 2017 10:22:00 -0300 Re: Drum feed water - By: [50] Mr. Tushar:<br /><br />I wonder if you mean to increase the feedwater temperature, for a design working pressure. If it were so, as Mr. Murphy stated, the limit is the saturation temperature. As far as I understand, there is always a certain margin, say some 10 to 15C, to avoid the risk of steaming in the economizer, because then the pump capacity may be impaired, for it is designed to pump liquids, not a gas.<br /><br />If steaming were marginal, the pump might still deliver the biphase flow, but compare with centrifugal compressors, they need a much higher rpm to compress gases than it is required for pumps, this is because of the low density of the gas as compared to a liquid.<br /><br />Reducing the margin will certainly increase the efficiency of the plant, but consider and evaluate it with caution, I feel it is risky.<br /><br />Claudio Molanes<br /><br /><br /><br /><br /><br /><br /> Tue, 13 Jun 2017 18:07:00 -0300 Re: Extraction turbine - By: Murphy [21] I think the extraction grid valve for bleed steam is before my time, but let me say this that the term was used by General Electric around 1920 to 1940 or there about on 1mw to 3mw STG. The design cam from the old Curtis Turbines that GE bought a century ago. I think Terry Turbine, Westinghouse Turbines used a steam extraction bleeder valve that differed, but did the same thing.<br /><br />These STG evolved and found new life in manufacturing plants today with better control devices.<br /><br />I have seen extraction steam turbines or bleeder turbines as I remember the guy that was with me called it, but they were not in use many years ago and were in an old manufacturing plant. In trying to visualize the bleeder mechanism is it seemed simple enough, but I seem to remember the mechanism being elegant which to me means it was sophisticated. It had 2 principle parts 1-the piston that moved the grid bleeder valve and 2- the mechanical controller that told the big piston to move. This was predicated on the desired extraction steam conditions going to the plant for process steam and steam heating. When there was no demand the grid bleeder valve closed off allowing the steam from the extraction or bleeder turbine to dump its worked steam to the surface condenser. All the time generating electricity.<br /><br />The governor would have been typical of that period and separate from the grid valve or bleeder valve. The governor was either a ball or weight speed regulation that was used with a fulcrum with leverage to a high press steam inlet valve and a low pressure valve if one was provided. Oil was used with a dash pot to settle out the unwanted movement.<br /><br />Someone may have a better memory than myself, but I think this is helpful for you. Tue, 13 Jun 2017 17:09:00 -0300 Re: Drum feed water - By: Murphy [21] If I understand you right, you want to increase the steam drum temperature to the maximum allowed. Of course the maximum allowed is stamped on the boiler and I would hope at the manway opening. So, this is the saturation steam pressure - temperature of the boiler should we be talking about a subcritical boiler.<br /><br />Can you clarify what you mean?<br /><br />Can you include a picture of the nameplate?<br /> Tue, 13 Jun 2017 14:32:00 -0300 Drum feed water - By: Tushar [2153] Sir,<br /><br />I wonder, what if we put water having higher approach point to drum?<br /><br />What are the maximum limits for approach point temperature?<br /><br />Please guide.<br /><br />Regards,<br />Tushar Mon, 12 Jun 2017 06:31:00 -0300 Re: Linearity tests - By: Ross [390] Linearity Testing as it relates to CEMS or Continuous Emission Monitoring is a laboratory analytical calibration technique that the distrusting EPA is demanding to be done in the field. This test requires skilled laboratory techniques. You judge for yourself.<br /><br />So the question begs to be asked that for any given method of analysis such as emission monitoring - is the relationship between the instrument readings test results and the actual concentration reasonably linear? The answer is 5 percent linearity is the maximum. This is a sophisticated analytical technique that cannot be taken lightly and done by research scientist in the past.<br /><br />The linearity test in a CEMS is basically a calibration check using calibrated gases that you purchase. 3 non-consecutive measurements should be made for each of the calibration gases at point zero, the low, then the mid, high, then again zero, low, mid, high, and again until done.<br /><br />The linearity specification should require that the mean difference between the calibration gas value and emission sampling responds at each of the four points -meaning at zero, low, mid, and high - and be calculated from three measurements. The mean difference at all four test points must be<br />less than 5 percent for SO2 and NOx monitors and 0.5 percent O2 or CO2.<br /><br />This linearity test is done after installation, when adjustments are done but not routine instrumentation drift, and done when repairs are needed, and at least quarterly. <br /><br />Ross Fri, 9 Jun 2017 15:13:00 -0300 closed feedwater heater - By: john [1794] What is the procedure for checking for air leaks in a high pressure feedwater heater? Thu, 8 Jun 2017 01:44:00 -0300 Linearity tests - By: john [1794] Could someone explain how linearity test are performed on cems? Thu, 8 Jun 2017 01:42:00 -0300