FI63799B - AONG- OCH KONDENSSYSTEM FOER PAPER MACHINE - Google Patents

Description

63799

The present invention relates to a system according to the preamble of claim 1.

The steam system of a paper machine consists of successive groups of drying cylinders. In the schematic example system of Figure 1, there are three groups of cylinders, but the number varies with different paper machines. The drying system may also comprise two separate steam systems, one before the gluing step and the other after.

In the drying cylinder, the steam transfers its heat of evaporation to heat the paper web. The condensate is collected in condensate tanks (LA), from where it is transferred by means of condensate pumps (LP) to the power plant's 1 s condensate system.

1) The removal of condensate from the cylinders requires a certain minimum pressure difference between the cylinder and the condensate vessel.

2) Due to the pressure difference, some (approx. 5 ··· Ί5%) of the steam entering the cylinder also enters the condensate vessel with the condensate. In order to minimize the amount of steam flowing through, the pressure difference must not exceed the minimum pressure difference mentioned above.

3) The flow-through steam is intended to be used in the next drying group. Due to the pressure drop, some of the condensate evaporates, so it can also be used in the next 25 groups. In order to transfer the flowing steam and the evaporating condensate, a sufficient pressure difference is required between the cylinders of the condensate vessel and the next drying group.

When driving with a small load or thin paper quality, the moisture in the paper web is already low before the last drying group.

30 The pressure of the last drying group is adjusted on the basis of the humidity controller (PC), so with a small load the the pressure is low. If the differential pressure profile is to be considered as complying with the above requirements, the pressure in the first group of condenser (LA1) must be reduced sufficiently. Ko. however, the pressure has a certain minimum value, 35 due to one of the following factors: - The condensate pump requires a certain minimum pressure on the suction side.

- The condenser has a minimum pressure due to the dimensioning of the heat transfer surface or the capacity of the air pump.

2 63799

With low loads and thin paper grades, the following situation is practically encountered: - To secure the pressure difference between the last cylinder group (KR3) and the condensate vessel (LA3), the control valve 5 (V7) is opened. Steam and vapor vapor Conducted at condensed time en.

- The steam entering the condenser is replaced in drying group 2 by opening the control valve (V2).

In this case, the above conditions 1) and 2) are met, 1 o but condition 3) is not fulfilled.

The object of the present invention is to provide a system by means of which the above-mentioned condition 3) is also fulfilled.

The invention is based on the following ideas: 1 5 The differential pressure profile can be changed, not only by lowering the initial pressure, but also by increasing the end pressure. The pressure setpoint of the last group is determined so that the drying power is given a certain value. If the heat transfer surface of the last group is reduced, the humidity controller increases the steam pressure to maintain the drying efficiency.

20 In practice, the heat transfer surface of the drying group can be reduced by closing some of the cylinders with shut-off valves connected to the steam inlet pipes.

More specifically, the system according to the invention is characterized essentially by what is set forth in the characterizing part of claim 1.

The invention provides considerable advantages. Thus, the amount of steam going to the condenser is reduced, so the energy and exergy economy of the paper machine is improved. At the same time, condensate removal from the cylinders is also ensured with small loads, thus avoiding the so-called

30 getting into a load of water. In addition, the preferred shape of the pressure and thus also the temperature profile of the drying cylinder system is ensured.

The system according to the invention will now be examined in more detail by means of an exemplary embodiment according to the accompanying drawings.

Figure 1 schematically shows, as already mentioned, one known steam and condensing system of a paper machine.

63799 3

Figure 2 schematically shows an embodiment of a system according to the invention.

The following process technical changes have been made to the known system according to Fig. 1 according to Fig. 2: 5 - The steam inlet pipes of the cylinders at the end of the last drying group KR3 are provided with shut-off valves SV1 ... 4.

- To remove leakage steam from closed cylinders, the condensate drain piping is connected to the vacuum system (condenser) via three-way valves KV1 ... 4.

10 When the pressure in the drying group drops so low that the above-mentioned condition 3) cannot be met, some of the shut-off valves SV1 ... 4 · are closed. At the same time, set the corresponding three-way valves KV1 ... 4 to the position corresponding to the vacuum system. To remove condensate from the leaking steam, open the drain valve TV at appropriate intervals.

1 5 Paper quality issues impose the following conditions on the system: - Closing the cylinders must start at the end of the last group KR3, as the surface temperature of the cylinders must rise or remain constant as the paper web moves 20 (from left to right in Figure 1).

- The cylinders must always be closed in groups of two (upper and lower cylinder) to keep the drying symmetrical.

Within the framework of the invention, it is also possible to think of solutions that differ from the embodiment described above. Thus, shut-off valves and condensate drain members can also be present in the previous cylinder groups KR1, KR2. It should also be mentioned that the control of the shut-off valves SV1 ... 4 of the steam cylinders can be carried out either manually or automatically. The operation of the automatic application when the load decreases can be, for example: 30 - Calculate the profile of the pulp power based on the mass and energy balances, - Calculate the required differential pressure profile, - Reduce the upstream pressure to the desired value (eg minimum), 35 closing the necessary number of steam cylinders and - taking into account the momentary decrease in heat output, e.g. by momentarily increasing the pressure setpoint of the last group KR3.

Claims (5)

63799 k A steam and condensing system for a paper machine comprising - a main steam pipe or the like, 5. at least two successive groups of drying cylinders (KR1 ... 3) with a plurality of drying cylinders, suitably arranged in pairs, - at least one first control valve (V1 ... 3) each cylinder group (KR1 ... 3) from the group (KR1 ... 3) to the cylinders 10 of the main steam pipe inlet side, - at least one condensate (LA1 ... 3) or the like for each cylinder group (KR1 ... 3) for receiving the condensate from from the outlet side of the cylinders of said group (KR1 ... 3) and 15. at least one second control valve (V4, V5) for each subsequent cylinder group (KR2, KR3) for connecting the condensate vessel (LA2, LA3) of said group (KR2, KR3) to the previous to the inlet side of the cylinders of the cylinder group (KR1, KR2), characterized in that at least some of the cylinders of the at least one cylinder group (e.g. KR3) are provided on their inlet side with their own shut-off valve (SV1 ... 4) for steam supply for switching off and on the output side, respectively, with means (KV1 ... 4 ·, TV) for connection to a vacuum system, e.g. a condenser, for removing leakage steam with the cylinder 25 closed. A system according to claim 1, characterized in that only the last cylinder group (KR3) has cylinders with said shut-off valves (SV1 ... 4-) and members (KV1 ... 4-, TV). 30 A system according to claim 1, characterized in that said means comprise a three-way valve (KV1 ... 4-) arranged in the condensate pipe of the cylinder. · 4. A system according to claim 1, characterized in that said means comprise a drain valve (TV) common to said cylinders 35. 5,63799