Steam balance flows

Table 3. Steam Balance, Flows in Metric Tons per Hour ...

Once the data are extracted, it is time to sketch a steam balance flow diagram (the so-called steam process flow diagram, PFD) and put these data together for each steam header in the PFD (Figure 16.1). The steam PFD is a very powerful visual aid as it allows an overview of a complex steam system at a glance. 

There are two ways of presenting steam balance data, schematically or tabulady. For both presentation types, a balance is made at each pressure level. In a schematic balance, such as that shown in Figure 9, horizontal lines are drawn for each pressure. The steam-using equipment is shown between the lines, and individual flows are shown vertically. Table 3 contains the same data as shown in Figure 9. In both cases the steam balance has been simplified to show only mass flows. A separate balance should be developed that identifies energy flows, including heat losses and power extraction from the turbines. 

Fig. 9. Schematic steam balance where the numbers represent steam flows in metric tons per hour. See Table 3.

Sometimes, conventional techniques do not produce a satisfactory steam balance for all operating modes. Options are available for steam drives for flexibility, such as extraction and induction turbines. Extraction turbines are widely used. In these, an intermediate pressure steam is removed or extracted from an intermediate turbine stage with the extraction flow varying as required over preset limits. Induction turbines are not as widely used as extraction turbines, but are a very satisfactory application... 

PERIOD = 1 is the heating period using a steam mass flow rate of Fs. The mass balance on the steam jacket determines the steam density ps, which together with a steam table function determines the temperature of the jacket Tj. 

Thus, in this example, assumption of the deaeration steam allows the steam balance to be closed. However, this is based on an assumed deaerator flow. The actual flow to the deaerator can be calculated from a heat balance around the deaerator. Figure 23.23 shows the flows into and out of the deaerator. If the boiler feedwater flow and condensate flows are known, together with an assumed value of the vent steam, then the flowrate of deaeration steam can be calculated from an energy balance. 

Complete the steam balance provided in Figure 23.57. a. Calculate extraction flows through 71 and T2... 

Montedison Low-Pressure Process. The Montedison low-pressure process [940], [1036], [1128], [1129] involves a split flow to two primary reformers. About 65% of the feed-steam mixture flows conventionally through the radiant tubes of a fired primary reformer followed by a secondary reformer. The balance of the feed-steam mixture passes through the tubes of a vertical exchanger reformer. This exchanger reformer has a tube sheet for the catalyst tubes at the mixed feed inlet. There is no tube sheet at the bottom of the tubes, where the reformed gas mixes directly with the secondary reformer effluent. The combined streams flow on the shell side to heat the reformer tubes in a manner similar to that described for the M. W. Kellogg KRES reformer, see Sections 4.1.1.8 and 5.1.4.3). The process air flow is stoichiometric. Synthesis is performed at 60 bar in a proprietary three-bed indirectly cooled converter with am-... 

The liquid of a tank is heated with saturated steam, which flows through a coil immersed in the liquid (Figure 10.2). The energy balance for the system yields... 

Steam letdown valves are used to give steam supply flexibility and temperature control. However, letdown steam represents lost opportunity for power generation. Steam balance optimization could minimize the letdown steam flow and henee reduee the loss in power-generating potential. 

As a guideline, an accuracy of at least 97, 95, and 90% should be maintained for HP, MP, and LP steam headers, respectively. The inaccuracy could be attributed by meter miscalibration, uncertainty in steam losses, and estimates for unmeasured flows. The most difficult task in making the steam balance is to balance the LP header with high accuracy as there are many unmeasured LP flows and losses all over the site, which are not measured. 

Until now, all the missing flows are resolved and the results are shown in Figure 16.5. The question is Is this steam balance converged You may think about it and the answer will be given later. 

With the DA steam of 19 klb/h newly calculated, the same procedure as above for calculating the missing flows is repeated to give the closed steam balance as shown in Figure 16.6. 

In the end of verification, the steam balance was modified with newly calculated flows to give the revised steam balance as shown in Figure 16.10. The imbalances are well within the best practice guideline. 

After all, as the simplest way to conclude, on-site power generation beats power import when on-site heat rate from certain turbine flow path beats market heat rate. In this case, maximize power generation through this turbine path while observing steam balance. If possible, surplus power generated is exported to grid. 

From the steam balance point of view (Figure 20.8), there is a large amount of HP and MP letdown flows, which is the source of inefficiency. Let us see if the F304 eonvection revamp project could help to mitigate this inefficiency. 

Steam balance comments From Figure 20.2 1. Will reduce boiler HP by lOOt/day 2. Will reduce I-P dump From Figure 20.4 Will reduce boiler steam by 200 t/day and has no effea on the rest of steam balance From Figure 20.8 HCU LP stripping steam demand will increase HP and MP letdown flows Rom Figure 20.9 Will reduce HP letdown by 85 t/day with the rest of the steam balance remained the same... 

EXAMPLE 2.7-1. Energy Balance on Steam Boiler Water enters a boiler at 18.33°C and 137.9 kPa through a pipe at an average velocity of 1.52 m/s. Exit steam at a height of 15.2 m above the liquid inlet leaves at 137.9 kPa, 148.9°C, and 9.14 m/s in the outlet line. At steady state how much heat must be added per kg mass of steam The flow in the two pipes is turbulent. 

Temperature Drop in Throttling Valve and Energy Balance. Steam is flowing... 

The measured fuel flows, arch oxygen composition, and high pressure steam drum heat balance confirm that the heat duties calculated from the process side (as opposed to the flue gas side) are most accurate, as would be expected. The high pressure steam system and boiler feed water measurements impact significantly on the convection section heat balance since boiler feed water preheat and steam superheat duties make up the majority of the convection section duty. The high pressure steam import flow, and the expected versus measured and calculated S5mthesis gas compressor steam turbine performance further support that the process side, and not the flue gas side measurements are the most accurate. 

The energy balance should analyse the energy flows by type and amount, ie, present summaries of electricity, fuel gas, steam level, heat rejected to cooling water, etc. It should include reaUstic loss values for turbine inefficiencies and heat losses through insulation. 

This reaction can also be mn in a continuous fashion. In the initial reactor, agitation is needed until the carbon disulfide Hquid phase reacts fully. The solution can then be vented to a tower where ammonia and hydrogen sulfide are stripped countercurrendy by a flow of steam from boiling ammonium thiocyanate solution. Ammonium sulfide solution is made as a by-product. The stripped ammonium thiocyanate solution is normally boiled to a strength of 55—60 wt %, and much of it is sold at this concentration. The balance is concentrated and cooled to produce crystals, which are removed by centrifiigation. 

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