Pressure control system, method and apparatus for controlling pressure

Abstract

The invention relates to a pressure control system, a method and an apparatus for controlling pressure. The pressure control system comprises at least one line and valve and the pressure control system controls the valve for arranging a desired pressure for at least one predetermined device. The pressure control system may comprise at least one pressure source (9), at least one pressure gauge (5) for measuring pressure and at least one pressure valve (7) for feeding pressure A from the pressure source, and a control unit for adjusting pressure B, which is lower than the pressure A, to a desired value based on a measurement of the pressure gauge in a process line of the pressure control system, and at least one valve (3,15,16) for supplying the pressure B from the process line to the predetermined device (1).

Description

[0001] PRESSURE CONTROL SYSTEM, METHOD AND APPARATUS FOR CONTROLLING PRESSURE

[0002] FIELD

[0003] The application relates to a pressure control system defined in claim 1, a method defined in claim 9 and an apparatus defined in claim 18 for controlling pressure .

[0004] BACKGROUND

[0005] It is known that pressure must be adjusted in different processes and apparatuses. Further, different pressure adjusting devices are known for adjusting pressure. However, it is challenging to keep pressure constant in various processes.

[0006] If the pressure cannot be kept unchanged in a reactor, process liquid may boil inside the reactor. The boiling causes dissolved material precipitations, peelings, and formations of undesired new compounds, e.g. furfural and hydroxymethyl furfural in the case of biomaterials. Further, when so called dissolving pulp is made, existing systems needs from time to time stopping of production and alkali washing because pre-hydrolysis system is clogged easily, due to precipitations of lignin and / or carbohydrates, originating from prehydrolysis liquid. Similar precipitation occurs in a normal chemical pulp Kraft cooking. The pulp is always flashed out from a reactor during emptying, which causes the precipitation of dissolved material, e.g. unwanted lignin on a surface of cellulose fiber. Then high chemical consumptions are caused later in O2-stage and in bleaching stages.

[0007] OBJECTIVE

[0008] The objective is to solve the above problems. Further, the objective is to disclose a new-type pressure control system for controlling and adj usting pressure . Further, the obj ective is to disclose a new method and apparatus for controlling and adj usting pressure . Further , the obj ective is to keep a pres sure unchanged during a process .

[0009] SUMMARY

[0010] The pressure control system, method and apparatus are characteri zed by what are presented in the claims .

[0011] The pressure control system for controlling pressure comprises at least one line and valve , and the pressure control system controls the valve for arranging a desired pressure for at least one predetermined device . The pressure control system comprises at least one pressure source , at least one pres sure gauge for meas uring pressure and at least one pressure valve for feeding a pressure A from the pressure source , and a control unit for adj usting a pressure B to a desired value in a process line of the pressure control system . Further, the pressure control system comprises at least one valve for supplying the pressure B from the process line, preferably to the predetermined device . The pressure control system controls the pressures A and B .

[0012] In the method for controlling pressure , the pressure is controlled using a pressure control system comprising at least one line and valve . The pressure control system controls the valve for arranging a desired pressure to at least one predetermined device . The pressure control system, comprising at least one pressure source , at least one pressure gauge for measuring pressure and at least one pressure valve for feeding a pressure A from the pressure source , is arranged to adj ust a pressure B to a desired value in a process line of the pressure control system . The pressure B is supplied via at least one valve from the process line to the predetermined device, and the pressures A and B are controlled using the pressure control system.

[0013] An apparatus for controlling pressure comprises at least one device and at least one pressure control system comprising at least one line and valve, in which the pressure control system controls the valve for arranging a desired pressure for at least one of the devices .

[0014] BRIEF DESCRIPTION OF THE DRAWING

[0015] The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate some embodiments of the invention and together with the description help to explain the principles of the invention. In the drawings:

[0016] Fig. 1 is a flow chart illustration of a process according to one embodiment,

[0017] Fig. 2 is a flow chart illustration of a process according to another embodiment, and

[0018] Fig. 3 is a flow chart illustration of a process according to another embodiment.

[0019] DETAILED DESCRIPTION

[0020] A pressure control system, i.e. a system, is disclosed for controlling pressure, e.g. in a predetermined process. The pressure control system comprises at least one line and valve, and the pressure control system controls the valve, e.g. by opening and closing the valve, for arranging a desired pressure for at least one predetermined device. The pressure control system may comprise more than one valves. The pressure control system comprises at least one pressure source, at least one pressure gauge for measuring pressure and at least one pressure valve, e.g. pressure IN valve, for feeding pressure A from the pressure source, and a control unit for adjusting pressure B to a desired value, which is lower than the pressure A, based on a measurement of the pressure gauge in a process line of the pressure control system, and at least one valve for supplying the pressure B from the process line to the predetermined device. Preferably, the pressure B is measured and / or adjusted. The pressure gauge is measuring the actual pressure, i.e. pressure B, in the process. The pressure B may be lower than pressure A due to non-linear characteristics of the pressure valve. The typical valves have always non-linear characteristics meaning that there is always a small error between a set value and an actual value in the process. Preferably, this small difference, i.e. the non-linear characteristics, is taken account when the pressure control system is controlled. In one embodiment, the pressure control system comprises at least one pressure OUT valve for releasing pressure from the process line based on a pressure C, which is set to a desired value being higher than the pressure A.

[0021] In the method for controlling pressure, e.g. in a predetermined process, the pressure is controlled using a pressure control system comprising at least one line and valve. The pressure control system controls the valve, e.g. by opening and closing the valve, for arranging a desired pressure to at least one predetermined device. The method comprises arranging the pressure control system, comprising at least one pressure source, at least one pressure gauge for measuring pressure and at least one pressure valve for feeding pressure A from the pressure source and a control unit to adjust pressure B to a desired value, which is lower than the pressure A, based on a measurement of the pressure gauge in a process line of the pressure control system, and supplying the pressure B via at least one valve from the process line to the predetermined device. Preferably, the pressure B is measured and / or adjusted. The pressure B may be lower than pressure A due to non-linear characteristics of the pressure valve. In one embodiment, the method further comprises releasing pressure from the process line based on a pressure C, which is set to a desired value being higher than the pressure A, via at least one pressure OUT valve.

[0022] Some embodiments of the pressure control system and the method are shown in Figs. 1, 2 and 3.

[0023] In this context, the process line means any line, pipe, tube or channel for transferring a desired pressure, e.g. from a pressure source to a predetermined process step or device. The process line can comprise one line part or more than one line parts. In one embodiment, the system comprises at least one process line, or more than one process lines, for arranging and supplying a desired pressure to a device. In one embodiment, the process line is a first line, second line or combination of the first and second lines.

[0024] The pressure control system comprises at least one valve or more than one valves. Any suitable valve can be used in the system. The valve may be a pressure valve, e.g. pressure control valve, or other suitable valve. In one embodiment, a pressure valve where pressure can be controlled in certain pressure limits can be used in the system. In one embodiment a valve for feeding pressure from the pressure source, i.e. from a first pressure source, such as pressure IN valve, and / or a valve for releasing pressure from a process line, such as pressure OUT valve, are the type of valves where pressure is controlled in certain limits. In one embodiment, the pressure valve is a pressure IN valve for feeding pressure from the pressure source to the process line. In one embodiment, the pressure valve is a pressure OUT valve for releasing pressure from the process line . In this context, the control unit means any control unit or control means, e.g. controls, control instrument, control device or the like, for controlling the pressures in the process line and / or for controlling the valves. The control using the control unit may be carried out automatically, with software, manually, mechanically or any combinations thereof.

[0025] In one embodiment, the pressure A is set to the desired value and the pressure B is adjusted based on the measurement of the pressure gauge such that the pressure is supplied from the pressure source to the process line of the pressure control system and the pressure valve is adjusted / controlled on grounds of the measurement of the pressure gauge, e.g. by checking the measurement values or by looking the pressure gauge.

[0026] In one embodiment, the pressure control system is integrated with a device. In one embodiment, the pressure control system is integrated with a device, and the pressure control system is arranged to adjust the pressure B for the device such that the pressure A is higher than the pressure B.

[0027] In this context, the device may mean any device which is pressurized. In one embodiment, the device is selected from the goup consisting of a reactor, digester, bleaching tower, liquid storage, tank, pumping system or any combination thereof.

[0028] In one embodiment, the pressure control system is integrated with a reactor, and the pressure control system is arranged to adjust the pressure B for the reactor such that the pressure A is higher than the pressure B. In this context, the reactor means any reactor which is pressurized.

[0029] In one embodiment, the pressure value A is selected or set based on non-linear characteristics of the pressure valve. In one embodiment, the pressure value A is 0.1 - 0.5 bar, in one embodiment 0.1 - 0.3 bar, in one embodiment about 0.2 bar, higher than pressure B, which can be used in a device, such as in a reactor. Preferably, pressure A is a pressure value, which is set to the pressure control system, and B is an actual pressure value. In one embodiment, the value A is B + nonlinear characteristics of the pressure valve. In one embodiment, the pressure B is lower than pressure A due to non-linear characteristics of the pressure valve.

[0030] In one embodiment, the pressure control system comprises the pressure source, the pressure gauge for measuring pressure and the pressure valve for feeding the pressure A from the pressure source and the control unit to adjust the pressure B, which is lower than the pressure A, based on the measurement of the pressure gauge in the process line of the pressure control system and the valve for supplying the pressure B from the process line to the predetermined device, and the pressure control system further comprises at least one pressure valve, e.g. pressure OUT valve, for releasing pressure from the process line based on a pressure C or D, which is set to a desired value being higher than the pressure A. The control unit can be arranged to control the pressures, e.g. pressures A, B and C / D, and / or the pressure valves.

[0031] In one embodiment, the pressure control system comprises the pressure source, the pressure gauge for measuring pressure and the pressure valve for feeding the pressure A from the pressure source and the control unit to adjust the pressure B, which is lower than the pressure A, based on the measurement of the pressure gauge in the process line of the pressure control system and the valve for supplying the pressure B from the process line to the predetermined device, and the pressure control system further comprises at least one pressure OUT valve for releasing pressure from the process line based on a pressure C, which is set to a desired value being higher than the pressure A, and the control unit is arranged to control automatically at least the pressure valve and the pressure OUT valve and at least pressure B, or the pressures A, B and C . In one embodiment , the method further comprises releasing pressure from the process line based on a pressure C, which is set to a desired value being higher than the pressure A, via at least one pressure OUT valve , and arranging the control unit to control automatically at least the pressure valve and the pres sure OUT valve and at least pressure B, or the pressures A, B and 0.

[0032] In one embodiment , the pressure control system is integrated with a process automation system, and the pressure control system is driven by the process automation based on the measurement of the pressure gauge . In one embodiment , the method comprises integrating the pressure control system with a process automation system, and driving the pressure control system by the process automation based on the measurement of the pressure gauge . In one embodiment , the pressure control system is connected to the process automation, and the pressure valves , such as pressure control valves , keeping pressure in certain limits are crucial part of system . When the pressure control system is driven by the process automation based on the measurement signal of the pressure gauge , the s ignals from the measurements are sent to pressure valves by taking account the set pressures A and C, and B is adj usted .

[0033] In one embodiment , pressure C is adj usted 0 . 1 - 0 . 5 bar, in one embodiment 0 . 1 - 0 . 3 bar, in one embodiment about 0 . 2 bar, over pressure A . Due to nonlinear characteristics of the pressure valve , pressure C is set at least a little over pressure A to ensure that the pressure OUT valve and the pressure valve , such as pressure IN valve , do not work against each other . Preferably, pressure C is a pressure value , which is set to the pressure control system . In one embodiment , the value C is A + non-linear characteristics of the pres sure valve , such as pressure OUT valve .

[0034] In one embodiment , the pressure control system comprises at least the pressure source , the pressure gauge for measuring pressure and the pressure valve , such as pressure IN valve , for feeding pressure A from the pressure source and the control unit to adj ust the pressure B, which is lower than the pressure A, based on the measurement of the pressure gauge in the process line of the pressure control system and the valve for supplying the pressure B from the process line to the predetermined device , wherein the process line is a first line , and the pressure control system further comprises at least one check valve for releas ing pressure from the first line to outside . Preferably, the pressure control system controls the pressures A and B for keeping the pressure B in the desired pressure value by adj usting the pressure valve and the check valve . Further, the pressure B can be adj usted to the desired value by means of the control unit .

[0035] In one embodiment , the method comprises arranging the pressure control system, comprising at least one pressure source , at least one pressure gauge for measuring pressure and at least one pressure valve , such as pressure IN valve , for feeding pressure A from the pressure source and the control unit to adj ust the pressure B, which is lower than the pressure A, based on the measurement of the pressure gauge in the process line of the pressure control system and the valve for supplying the pressure B from the process line to the predetermined device , and the method further comprises releasing pressure from the process line , which is a first line , to outside using at least one check valve of the pressure control system, in order to form, i . e . adj ust and / or keep, the desired pressure B, and controlling the pressures A and B using the pressure control system for keeping the pressure B in the desired pressure value by adjusting the pressure valve and the check valve. Further, the pressure B can be adjusted to the desired value by means of the control unit.

[0036] In one embodiment, the pressure control system comprises at least one second pressure source, at least one valve for feeding pressure from the second pressure source to a second line of the pressure control system, at least one second pressure gauge for measuring overpressure in the second line and at least one pressure valve, such as pressure OUT valve, for releasing pressure from the second line. The second pressure source, the valve, the second pressure gauge and pressure OUT valve can be arranged to set a pressure D to a desired value in the second line, wherein the pressure control system controls the pressure D for adjusting the pressure D higher than the pressure A. Further, the pressure D can be adjusted to the desired value by means of the control unit.

[0037] In one embodiment, the pressure is adjusted such that at least one second pressure source feeds pressure to a second line of the pressure control system via at least one valve such that overpressure is measured in the second line by at least one second pressure gauge and pressure is released via at least one pressure valve, such as pressure OUT valve, from the second line and a pressure D is set to a desired value in the second line using the second pressure source, the valve, the second pressure gauge and pressure OUT valve, wherein the pressure D is adjusted higher than the pressure A.

[0038] In one embodiment, pressure D is adjusted 0.1 - 0.5 bar, in one embodiment 0.1 - 0.3 bar, in one embodiment about 0.2 bar, over pressure A. Due to nonlinear characteristics of the pressure valve, pressure D is set at least a little over pressure A to ensure that the pressure OUT valve and the pressure IN valve do not work against each other . Preferably, pres sure D is a pressure value , which is set to the pressure control system . In one embodiment , the value D is A + non-linear characteristics of the pressure valve , such as pressure OUT valve .

[0039] When the pressure control system is driven manually or mechanically, the measurements of the pressure gauge and the pressure A and / or D, which have been set , are taken account , and B is adj usted based on the measurements of the pressure gauge .

[0040] In one embodiment, the pressure control system comprises at least one valve for combining the second line to the first line . In one embodiment , the second line is combined to the first line by a valve .

[0041] In one embodiment, the pressure source and / or the second pressure source is formed by using gas or liquid, preferably depending on which is suitable in the process . In one embodiment, the pressure source , such as a first pressure source, is formed by using gas or liquid . In one embodiment, the second pressure source is formed by using gas or liquid . In one embodiment , the pressure source and the second pressure source are formed by using gas or liquid . In one embodiment , the pressure is formed from gas or liquid to provide the pressure source and / or the second pressure source .

[0042] An apparatus for controlling pressure comprises at least one device and at least one pressure control system comprising at least one line and valve , in which the pressure control system controls the valve for arranging a desired pressure for at least one of the devices . The pressure control system comprises at least one pressure source , at least one pressure gauge for measuring pressure and at least one pressure valve , such as pressure IN valve , for feeding pressure A from the pressure source , and a control unit for adj usting a pressure B, which is lower than the pressure A, to a desired value based on a measurement of the pressure gauge in a process line of the pressure control system, and at least one valve for supplying the pressure B from the process line to the device , and the pressure control system is arranged to control the pressures A and B for keeping the pressure B in the desired pressure value for the device . The pres sure control system, as def ined in this description , may be used in the apparatus . In one embodiment , the pressure control system comprises at least one pressure OUT valve for releasing pressure from the process line based on a pressure C, which is set to a desired value being higher than the pressure A .

[0043] In one embodiment , the pressure control system comprises the pressure source , the pressure gauge for measuring pressure and the pressure valve for feeding the pressure A from the pressure source and the control unit to adj ust the pres sure B , which i s lower than the pressure A, based on the measurement of the pressure gauge in the process line of the pressure control system and the valve for supplying the pressure B from the process line to the device , and the pressure control system further comprises at least one pressure OUT valve for releasing pressure from the process line based on a pressure C, which is set to a desired value being higher than the pressure A, and the control unit is arranged to control automatically at least the pressure valve , e . g . pressure IN valve , and the pressure OUT valve and at least pressure B, or the pressures A, B and 0.

[0044] In one embodiment , the pressure control system comprises the pressure source , the pressure gauge for measuring pressure and the pressure valve for feeding the pressure A from the pressure source and the control unit to adj ust the pres sure B , which i s lower than the pressure A, based on the measurement of the pressure gauge in the process line of the pressure control system and the valve for supplying the pressure B from the process line to the device, wherein the process line is a first line , and the pressure control system further comprises at least one check valve for releasing pres sure from the first line to outside . Preferably, the pressure control system is arranged to control the pressures A and B for keeping the pressure B in the desired pressure value for the device by adj usting the pressure valve and the check valve . In one embodiment , the pressure control system further comprises at least one second pressure source , at least one valve for feeding pressure from the second pressure source to a second line of the pressure control system, at least one second pressure gauge for measuring overpres sure in the second line and at least one pres sure OUT valve for releasing pressure from the second line , and the second pressure source , the valve , the second pressure gauge and pressure OUT valve are arranged to set a pressure D to a desired value , which is higher than the pressure A, in the second line , wherein the pressure control system controls the pressures A, B and D . In one embodiment, the pressure control system further comprises at least one valve , such as a valve or more than one valves , for combining the second line to the first line .

[0045] In one embodiment, the device is selected from the group consisting of a reactor, digester, bleaching tower, liquid storage , tank, pumping system, or any combination thereof . In one embodiment, the apparatus comprises at least the reactor . In one embodiment , the apparatus comprises at least the reactor and liquid storage or tank . In one embodiment , the apparatus comprises at least the pumping system . In one embodiment , the apparatus comprises at least the pumping system and the liquid storage or tank . In one embodiment , a pulsation may form during pumping, e . g . during pumping of liquid or fluid from a storage, and pressure is adjusted using the pressure control system.

[0046] In one embodiment, the apparatus comprises at least one pipe system comprising at least one valve for connecting two devices, e.g. a reactor and a liquid storage, to each other.

[0047] In one embodiment, the pressure control system is connected to the device or devices, e.g. reactor and / or liquid storage, via at least one valve, more than one valve, or line(s) and valve (s) . By means of valve the device can be connected and disconnected to the pressure control system and from the pressure control system.

[0048] In one embodiment, the apparatus comprises a heating system for heating the device, e.g. reactor and / or liquid storage to desired temperature level.

[0049] In one embodiment, the apparatus comprises at least one cooling device for cooling a material which is taken out from a reactor. In one embodiment, an output of the reactor is equipped with a heat exchanger. In one embodiment, the apparatus comprises the cooling device, e.g. a heat exchanger, cold water cooling, cooling with other cooling media or other suitable cooling device, in a line where the material comes out from the reactor.

[0050] In one embodiment, all valves of pressure control system are closed at the start of operations.

[0051] In one embodiment, all valves of pressure control system are closed at the start of operations. Pressures values A, B and C are set to a process automation which controls the pressure valves, such as the pressure valve and pressure OUT valve, by detecting measurement signals from the pressure gauge and sending the signals to the pressure valves. Pressure of the pressure source is turned on. By the control of process automation and signals from pressure gauge, the pressure IN valve is opened as much as the pressure reaches the pressure A. Further , at the same time due to non-linear characteristics of the pressure IN valve , the pressure B reaches the right level , as well as pressure C . Thus , the pressures A, B and C are set to right level by driving by the process automation system . The pressure control system keeps pressure B unchanged, preferably in a device . The control pressure system is driven by the process automation or the process automation system using the measurement data, e . g . signals , of the pressure gauge and by sending the data to the pressure valves and by taking account pressure values A, B and / or C .

[0052] In one embodiment, all valves of pressure control system are closed at the start of operations . Pressure of the pressure source is turned on, and by looking a pressure gauge , pressure A is set to a desired value by adj usting the pressure IN valve , and further, by opening up a check valve , which releases system pressure to outside , pressure B is checked . After that the check valve can be closed . Thus , the pressure B and the pressure A can be adj usted . The pressure control system keeps pressure B unchanged, preferably in a device .

[0053] In one embodiment , pressure of the second pressure source is turned on, and a valve is opened for feeding pressure from the second pressure source , and by looking a second pressure gauge , pressure D is set to a desired value by adj usting a pressure OUT valve . After that the valve for feeding pressure can be closed and the second pressure source can be connected out from the system . Thus , the system overpressure D can be set . I f the pressure increases over pressure D, the pressure control system releases overpressure outside via the pressure OUT valve .

[0054] I f the pressure B decreases in the process line , the pressure from the pressure source can be added to the process line . Preferably, the pressure value of the pressure B is measured in the process line during the process, i.e. B is an actual pressure value, e.g. cooking pressure of the process.

[0055] In one embodiment, the pressure control system can be used in a continuous process, e.g. in a chemical process, a treatment of biomaterial, pulp technology process, or the like.

[0056] In one embodiment, the pressure control system, as described above in the text, is integrated to a process in which biomaterial, such as wood-based material or biomass, is treated, or in which cellulose-based material is treated, or in which microcellulose, e.g. microcrystalline cellulose, is produced, or in which chemical pulp, e.g. kraft pulp or dissolving pulp, is produced, or any combination of thereof. In one embodiment, the pressure control system is integrated to a process in which the cellulose-based material is fractionated to different components in order to separate cellulose, hemicelluloses and lignin. In one embodiment, the pressure control system is used in a hot water system or an alkali system. In one embodiment, the pressure control system is used in a hot water extraction.

[0057] It has now been surprisingly found that the pressure can be adjusted easily, and the pressure can be kept unchanged easily during the process. It is important to keep the pressure unchanged during the process. For example, in one embodiment, if the pressure is not constant during the treatment of the biomaterial, the biomaterial may start to boil. The pressure control system enables to control pressures also in emptying of reactors. This prevents many problems occurring in a chemical industry, e.g. in a chemical pulping industry.

[0058] The pressure control system can also improve pumping processes. When vessels, tanks, reactors or the like are emptied, the pressure system equalizes the pressure in these devices, and pumps in the outlet of these devices work normally without any cavitation or other relating problems, caused by pressure differences of device-pump systems.

[0059] The pressure control system, method and apparatus offer a possibility to control and adjust pressures easily, and energy- and cost-effectively in the processes and devices, e.g. reactors. The present invention provides an industrially applicable, simple and affordable way to produce an effective pressure arrangement. The pressure control system and method are easy and simple to realize in connection with different production processes and devices.

[0060] EXAMPLES

[0061] Figs. 1, 2 and 3 present some embodiments of the pressure control in the process.

[0062] The process of Figs. 1 and 2 comprises a reactor (1) for treating a desired feed, e.g. wood-based material or biomass, to form a product, and a liquid storage (12) for feeding the feed to the reactor.

[0063] Further, the process of Figs. 1, 2 and 3 comprises a pressure control system for controlling pressure. The pressure control system comprises several valves and at least one process line. The pressure control system controls the valves for arranging a desired pressure for the reactor (1) and liquid storage (12) . The pressure control system comprises a pressure source (9) , i.e. a first pressure source, a pressure gauge (5) for measuring pressure and a pressure IN valve (7) for feeding pressure A from the pressure source (9) . Further, the pressure control system comprises a control unit for adjusting a pressure B to a desired value, which is lower than the pressure A, based on a measurement of the pressure gauge (5) in a process line, and at least one valve (3,15,16) for supplying the pressure B from the process line to the reactor and / or liquid storage. Further, the pressure control system of Figs. 2 and 3 comprises a check valve (8) for releasing pressure from the first line to outside. The pressure control system controls the pressures A and B for keeping the pressure B in the desired pressure value by adjusting the pressure IN valve (7) and / or the check valve (8) .

[0064] Further, the pressure control system of Fig. 1 comprises at least one pressure OUT valve (6) for releasing pressure from the process line based on a pressure C, which is set to a desired value being higher than the pressure A. The control unit is arranged to control automatically the pressure valves, such as the pressure IN valve (7) and the pressure OUT valve (6) , and the pressures A, B and 0. The pressure control system can be integrated with a process automation system, and the pressure control system is driven by the process automation based on the measurement of the pressure gauge (5) . In Fig. 1 the pressure B may be supplied from the process line to the reactor and / or liquid storage between the pressure IN valve (7) and the pressure OUT valve ( 6) .

[0065] Further, the pressure control system of Figs. 2 and 3 comprises a second pressure source (11) , a valve (17) for feeding pressure from the second pressure source to a second line of the pressure control system, a second pressure gauge (4) for measuring overpressure in the second line and a pressure OUT valve (6) for releasing pressure from the second line. The second pressure source (11) , the valve (17) , the second pressure gauge (4) and pressure OUT valve (6) are arranged to set a pressure D to a desired value in the second line. The pressure control system controls the pressure D for adjusting the pressure D higher than the pressure A. The second line is combined to the first line via a valve (2) . In Figs. 2 and 3 the pressure B may be supplied from the process line to the reactor and / or liquid storage between the first and second lines, such as between the pressure IN valve (7) and the pressure OUT valve (6) , and / or between valves (2) and (3) .

[0066] The pressure IN valve (7) and the pressure OUT valve (6) are the type of valves where pressure is controlled in certain limits.

[0067] The pressure control system can be used effectively in the process, according to the Figs. 1 - 3.

[0068] In one example, in the automatic pressure control system integrated with a process automation, all valves of pressure control system are closed at the start of operations. Pressures values A, B and 0 are set to a process automation which controls the pressure IN valve

[0069] (7) and the pressure OUT valve (6) , by detecting measurement signals from the pressure gauge and sending the signals to the pressure valves (6,7) . Pressure of the pressure source (9) is turned on. By the control of process automation and signals from pressure gauge, the pressure IN valve (7) is opened as much as the pressure reaches the pressure A. At the same time, due to nonlinear characteristics of the valve, the pressure B reaches the right level, as well as pressure C. Thus, the pressures A, B and C are set to right level. The control pressure system is driven by the process automation using the measurement data of the pressure gauge and by sending the data to the pressure valves and by taking account pressure values A, B and / or C.

[0070] In one example, in the mechanical pressure control system, all valves of pressure control system are closed at the start of operations. Pressure of pressure source (9) is turned on. By looking a pressure gauge (5) , pressure A is set to a desired value by adjusting pressure IN valve (7) . The pressure value A is around 0.2 bar higher than pressure B, which is used in a reactor (1) . By opening up, e.g. a little, a check valve

[0071] (8) , which releases system pressure to outside, pressure B is checked. After that check valve (8) is closed. If pressure B is not in the right value, i.e. it is too high or too low, necessary adjustments are made according to above mentioned procedures by adjusting the pressure IN valve (7) , and checking right pressure B level via the check valve (8) . Thus, a cooking pressure, i.e. pressure B, and pressure A, are adjusted. When chemical reactions are done in the reactor, the pressure control system keeps the used system pressure in pressure value B. If the pressure decreases under pressure B, the pressure control system feds more pressure to the system from the pressure source (9) , preferably not more than pressure A. Pressure (OUT) of the second pressure source (11) is turned on, and valve (17) is opened for feeding pressure from the second pressure source. By looking a second pressure gauge (4) , pressure D is set to a desired value by adjusting a pressure OUT valve (6) . Pressure D is adjusted around 0.2 bar over that pressure A. After that the valve (17) is closed and the second pressure source is connected out from the system. Thus, the system overpressure D is set. If the pressure increases over pressure D, the pressure control system releases overpressure outside (10) via the pressure OUT valve (6) . Pressure D have to be at least a little over pressure A to ensure that two valves, i.e. the pressure OUT valve (6) and the pressure IN valve (7) , are not working against each other.

[0072] The pressure source (9) and the pressure source (11) are created by using gas or liquid depending on which is suitable in the process.

[0073] According to the example, the pressure control system is used for controlling reactor system. After carrying out the adjustment of the pressure control system, as described above, following steps are performed. The reactor (1) and the liquid storage (12) are connected to each other via pipe system, where is a valve (13) . The pressure control system is connected to the reactor (1) and to the liquid storage (12) via lines and valves (15) and (16) of said lines. The valves (15) and (16) connect and disconnect the reactor (1) and the liquid storage (12) to the system and from the system. In the reactor (1) there is a pipe, which leads out from the reactor, and the pipe comprises a valve (14) . This valve (14) keeps, and releases material from reactor (1) . When the pressures A, B and C / D are adjusted to right level, the valves (2) , (3) , (15) and (16) are opened. The valve (13) is still closed, as also the valve ( 14 ) .

[0074] In this example, the heating system can be turned on to heat up the reactor (1) , and the liquid storage (12) to desired temperature level, which hits the pressure B. The reactor contains a reaction medium what typically is liquid, active chemical, and processed material. After a certain time, when the reaction is stopped, temperature can be decreased using the reactor heating system. However, the pressure may be kept in certain level by the pressure control system, without depending on used reaction temperature or temperature increase or decrease.

[0075] The pressure control system ensures that, if during the reaction the pressure inside the reactor (1) is trying to change due to some reasons, the pressure is forced always kept in certain level. Typical situations, in which the pressure is changed inside the reactor, are chemical reactions where components inside the reactor are peeled down and gas is formed.

[0076] The valve (14) is opened when the material is wanted to take out from the reactor (1) . The pressure control system enables pressure control inside the reactor (1) during emptying via the valve (14) . Thus, the pressure B is always maintained inside the reactor (1) , also during the emptying of the reactor via valve (14) . This prevents boiling of the material inside the reactor. The boiling would cause dissolved material precipitation, peeling, and formation of unwanted new compounds, e.g. furfural and hydroxymethyl furfural in the case of biomaterials.

[0077] In the presented system the liquid storage (12) enables displacement of the material inside the reactor (1) with desired chemical or just with water. This can be performed by closing the valve (15) , and by opening the valve (13) . When the valve (14) is opened, reactor (1) is emptied, and in the same time liquid from the liquid storage (12) flows to the reactor (1) through the valve (13) . Then the pressure control system is controlling the pressure inside the liquid storage (12) , and due to opening of the valve (13) , it is also controlling the pressure of the reactor (1) via hydrostatic forces .

[0078] An output of the reactor (1) can be equipped with a heat exchanger (18) . The heat exchanger can be arranged in the pipe before the valve (14) . This enables to cool a material flow outside from the reactor (1) . Further, the heat exhanger (18) enables heat recovery from heat of the reactor. Alternatively, cooling can be also carried out by using cold water cooling to the same line where the material comes out from the reactor (1) . In one embodiment, the heat exchanger is especially practical in force circulation digesters where only liquid flows and a material stays inside a reactor vessel.

[0079] The valve (14) is closed when emptying of the reactor (1) has been done.

[0080] The pressure control system is connected off, from the reactor and / or liquid storage by closing the valves (15) and / or (16) .

[0081] If different cooking temperatures are used in next reactions, pressures A, B and C / D are adjusted to desired new levels. Example 1

[0082] In this example, a reactor system with a pressure control system was used in the process based on Fig. 2.

[0083] The reactor system (70dm3) having a pressure control system was used to process wheat straw by using hot water extraction process. The pressures A, B, and D of the pressure control system were adjusted to values 5.2 bar, 5.0 bar, and 5.4 bar respectively.

[0084] 70dm3reactor vessel equipped with a jacket heating was loaded with the wheat straw and water. Straw amount was 1.323kg, and dry consistency 93.0%. Water amount was 50kg. The reactor was heated up to 152°C, by using an external thermal oil circulation system through the jacket. Heating period took 55min. A hot water extraction stage at 152°C lasted 118 minutes. Liquid samples were taken from the reactor during the cooking and pH values were measured: pH 7.0 (heat up period) , pH 5.7 (time when reaction temperature was reached) , pH 5.1 (in the middle of reaction) , and pH 4.7 just before the stopping of reaction. The samples were taken such that the pressure control system kept pressure inside the reactor in the same value, and sampling did not decrease pressure and did not cause boiling.

[0085] After the hot water extraction, the reactor was cooled down to 95°C in 20 min. The pressure was not decreased inside the reactor. In atmospheric conditions, system pressure was released and liquid inside the reactor was taken out via line in the bottom of reactor, by opening the valve (14) . pH was decreased during the reaction, being 4.7 at the end. The pressure was the same all the time inside the reactor. Thus, during the reaction there was no situation, due to pressure drop or increase, that reaction media would boil. All the temperature changes were made under the same pressure. The hot water extraction yield was 75%. The reactor liquid had neutral, plum like smell, but not any acetic scents.

[0086] Further, a reference hot water extraction was carried out. Similar hot water extraction was made using the same reactor setup, procedures, and raw material, but without the pressure control system. At the end of reaction stopping was made like usually done in an industry, by flashing liquid out from the reactor. Thus, the pressure was decreased, and a reactor media was let to flow out from the reactor freely, which also caused boiling of the liquid. In this case the end pH was 3.5. This means that so called autohydrolysis happened during the hot water extraction. In the autohydrolysis, the material which is extracted from solid fraction to dissolved form is peeled down, and acidic products are formed. Especially in the case of straw, acetic acid is usually formed. The reactor liquid had clear bitter acetic smell. The hot water extraction yield was 79%.

[0087] Example 2

[0088] The similar trial was made like in Example 1, but with some exceptions. In this example, heating period took 60 min, and a hot water extraction lasted at 153°C 115 min. After the hot water extraction liquid inside the reactor was taken out via a line in the bottom of the reactor, by opening valve (14) , and at the same time by displacing a reactor media with water, having same temperature than in the reactor, which came from the liquid storage (12) using procedures described earlier. The idea of using of liquid storage was to wash material inside the reactor (1) and to ensure that there was not any reaction liquid left among products. Displacement liquid amount was 150 kg. There was a heat exchanger in an output line of the reactor for avoiding liquid boiling when coming out from the reactor. During the purging of the reactor the pressure control system kept pressure inside the reactor unchanged. pH in the end of this trial was 4.6. The reactor liquid had neutral, plum like smell, but not any acetic scents. The hot water extraction yield was 73%.

[0089] Carbohydrate analyses were made from all three liquids according to analytical procedure of NREL Determination of Sugars, Byproducts, and Degradation Products in Liquid Fraction Process Samples - Laboratory Analytical Procedure (LAP) - Issue Date: 12 / 08 / 2006 - A. Sluiter, B. Hames, R. Ruiz, C. Scarlata, J. Sluiter, and D. Templeton. This procedure detects only monosaccharides, leaving oligosaccharides unanalyzed.

[0090] Liquid analyses were compared before and after autoclave processing made according to NREL procedure. In example 1 and example 2 the carbohydrate contents before autoclaving were 89.6%, and 91.4% smaller than after processing. This means that the so called monosugar content was considerably smaller in those hydrolysates, meaning that a major part of the carbohydrates were in oligomer form. In the reference sample carbohydrate content difference was only 4.5%, when comparing results before and after autoclaving, meaning that a major part of the carbohydrates was already in the monomer form after cooking. Thus, the pressure control system controlled hot water extraction prevents any kind of pressure changes in the process and in that way prevents also boiling of liquids in the process being simple way to produce oligosaccharides from biomasses.

[0091] Example 3

[0092] By using the same reactor system, the pressure control system, and the procedures than in Example 2, 2000 g of pine wood chips originating from Kemijarvi, were hot water exracted at temperature 160°C. The water amount in this experiment was 54000 g. Heating period lasted 63 min, and extraction 148 min. Liquid samples were taken during the hot water extraction at times 83 min, 113 min, 143 min, and in the end after 148 min. pH values were 5.33, 4.66, 4.32, and 4.25 respectively. Reference hot water extraction was made similarly than in Example 1 (reference trial) . This means that liquid was flashed out from the reactor, letting it boil in the outlet of the reactor. An end pH was 3.3 in the reference hot water extraction, meaning that a degradation of dissolved material occurred, which was noticed from the liquid having strong acetic scent.

[0093] It was observed from the tests of Examples 1- 3 that it is important to control the reactor pressure in the case of biomass processing. By doing that, it is possible to reduce and / or prevent dissolved amount peeling or degradation reactions. This opens the possibility to produce oligosaccharides from the different biomasses. The pressure control system enables improvements in several processes and process steps in the biomass processing industry. For example, the production of dissolving pulp from wood chips can be improved, in which one big problem is typically precipitations and blockings in a pre-hydrolysis stage. This is caused by high pressure drops, when a pre-hydrolysis liquid is flashed out from reactor. Further, when hot and pressurized reactors are emptied, an empty space remains in the upper parts of the reactors. This creates a vacuum to this space, and due to the high heat, boiling occurs. The pressure control system prevents this kind of situation, especially in the biomass processing.

[0094] The devices, reactors, storages, lines and valves, and other devices and equipments of the process used in Figs. 1, 2 and 3 and in Examples 1 - 3 are known per se in the art, and therefore they are not described in any more detail in this context .

[0095] The pressure control system, method and apparatus are suitable in different embodiments for adj ust- ing, controlling and keeping the pressure in different processes .

[0096] The invention is not limited merely to the examples referred to above ; instead, many variations are possible within the scope of the inventive idea defined by the claims .

Claims

CLAIMS1. A pressure control system for controlling pressure, in which the pressure control system comprises at least one line and valve and the pressure control system controls the valve for arranging a desired pressure for at least one predetermined device, c h a r a c t e r i z e d in that the pressure control system comprises- at least one pressure source (9) , at least one pressure gauge (5) for measuring pressure and at least one pressure valve (7) for feeding pressure A from the pressure source, and a control unit for adjusting pressure B, which is lower than the pressure A, to a desired value based on a measurement of the pressure gauge in a process line of the pressure control system, and- at least one valve (3,15,16) for supplying the pressure B from the process line to the predetermined device (1) .

2. The pressure control system according to claim 1, c h a r a c t e r i z e d in that the pressure control system is integrated with a reactor (1) , and the pressure control system is arranged to adjust the pressure B such that the pressure A is higher than the pressure B.

3. The pressure control system according to claim 1 or 2, c h a r a c t e r i z e d in that the pressure control system comprises the pressure source (9) , the pressure gauge (5) for measuring pressure and the pressure valve (7) for feeding the pressure A from the pressure source and the control unit to adjust the pressure B, which is lower than the pressure A, based on the measurement of the pressure gauge in the process line of the pressure control system and the valve for supplying the pressure B from the process line to the predetermined device (1) , and the pressure control systemfurther comprises at least one pressure OUT valve (6) for releasing pressure from the process line based on a pressure C, which is set to a desired value being higher than the pressure A, and the control unit is arranged to control automatically the pressure valve (7) and the pressure OUT valve (6) and the pressures A, B and 0.

4. The pressure control system according to claim 3, c h a r a c t e r i z e d in that the pressure control system is integrated with a process automation system, and the pressure control system is driven by the process automation based on the measurement of the pressure gauge.

5. The pressure control system according to claim l or 2, c h a r a c t e r i z e d in that the pressure control system comprises the pressure source (9) , the pressure gauge (5) for measuring pressure and the pressure valve (7) for feeding the pressure A from the pressure source and the control unit to adjust the pressure B, which is lower than the pressure A, based on the measurement of the pressure gauge in the process line of the pressure control system and the valve for supplying the pressure B from the process line to the predetermined device (1) , wherein the process line is a first line, and the pressure control system further comprises at least one check valve (8) for releasing pressure from the first line to outside, wherein the pressure control system controls the pressures A and B for keeping the pressure B in the desired pressure value by adjusting the pressure valve (7) and the check valve (8) .

6. The pressure control system according to claim 5, c h a r a c t e r i z e d in that the pressure control system further comprises at least one second pressure source (11) , at least one valve (17) for feeding pressure from the second pressure source to a second line of the pressure control system, at least one secondpressure gauge (4) for measuring overpressure in the second line and at least one pressure OUT valve (6) for releasing pressure from the second line, and the second pressure source (11) , the valve (17) , the second pressure gauge (4) and pressure OUT valve (6) are arranged to set a pressure D to a desired value in the second line, wherein the pressure control system controls the pressure D for adjusting the pressure D higher than the pressure A.

7. The pressure control system according to claim 6, c h a r a c t e r i z e d in that the pressure control system further comprises a valve (2) for combining the second line to the first line.

8. The pressure control system according to any one of claims 1 to 7, c h a r a c t e r i z e d in that the pressure source (9) and / or the second pressure source (11) is formed by using gas or liquid.

9. A method for controlling pressure, in which the pressure is controlled using a pressure control system comprising at least one line and valve and in which the pressure control system controls the valve for arranging a desired pressure to at least one predetermined device, c h a r a c t e r i z e d in that the method comprises- arranging the pressure control system, comprising at least one pressure source (9) , at least one pressure gauge (5) for measuring pressure and at least one pressure valve (7) for feeding pressure A from the pressure source and a control unit to adjust pressure B, which is lower than the pressure A, to a desired value based on a measurement of the pressure gauge in a process line of the pressure control system, and- supplying the pressure B via at least one valve (3,15,16) from the process line to the predetermined device (1) .

10. The method according to claim 9, c h a r a c t e r i z e d in that the pressure A is set to the desired value and the pressure B is adjusted based on the measurement of the pressure gauge such that the pressure is supplied from the pressure source (9) to the process line of the pressure control system and the pressure valve (7) is adjusted on the grounds of the measurement of the pressure gauge (5) .

11. The method according to claim 9 or 10, c h a r a c t e r i z e d in that the pressure control system is integrated with a reactor (1) , and the pressure control system is arranged to adjust the pressure B for the reactor such that the pressure A is higher than the pressure B.

12. The method according to any one of claims 9 to 11, c h a r a c t e r i z e d in that the method further comprises releasing pressure from the process line based on a pressure C, which is set to a desired value being higher than the pressure A, via at least one pressure OUT valve (6) , and arranging the control unit to control automatically the pressure valve (7) and the pressure OUT valve (6) and the pressures A, B and C.

13. The method according to claim 12, c h a r a c t e r i z e d in that the method comprises integrating the pressure control system with a process automation system, and driving the pressure control system by the process automation based on the measurement of the pressure gauge.

14. The method according to any one of claims 9 to 11, c h a r a c t e r i z e d in that the method further comprises releasing pressure from the process line, which is a first line, to outside using at least one check valve (8) of the pressure control system, in order to form the desired pressure B, and controlling the pressures A and B using the pressure control system for keeping the pressure B in the desired pressure value byadjusting the pressure valve (7) and the check valve(8) .

15. The method according to claim 14, c h a r a c t e r i z e d in that the pressure is further adjusted such that at least one second pressure source (11) feeds pressure to a second line of the pressure control system via at least one valve (17) such that overpressure is measured in the second line by at least one second pressure gauge (4) and pressure is released via at least one pressure OUT valve (6) from the second line and a pressure D is set to a desired value in the second line using the second pressure source (11) , the valve (17) , the second pressure gauge (4) and pressure OUT valve (6) , wherein the pressure D is adjusted higher than the pressure A.

16. The method according to claim 15, c h a r a c t e r i z e d in that the second line is combined to the first line by a valve (2) .

17. The method according to any one of claims 9 to 16, c h a r a c t e r i z e d in that the pressure is formed from gas or liquid to provide the pressure source(9) and / or the second pressure source (11) .

18. An apparatus for controlling pressure, in which the apparatus comprises at least one device (1, 12) and at least one pressure control system comprising at least one line and valve and in which the pressure control system controls the valve for arranging a desired pressure for at least one of the devices (1,12) , c h a r a c t e r i z e d in that- the pressure control system comprises at least one pressure source (9) , at least one pressure gauge (5) for measuring pressure and at least one pressure valve (7) for feeding pressure A from the pressure source, and a control unit for adjusting pressure B, which is lower than the pressure A, to a desired value based on a measurement of thepressure gauge in a process line of the pressure control system, and at least one valve (3,15,16) for supplying the pressure B from the process line to the device (1,12) , and- the pressure control system is arranged to control the pressures A and B for keeping the pressure B in the desired pressure value for the device.

19. The apparatus according to claim 18, c h a r a c t e r i z e d in that the pressure control system comprises the pressure source (9) , the pressure gauge (5) for measuring pressure and the pressure valve (7) for feeding the pressure A from the pressure source and the control unit to adjust the pressure B, which is lower than the pressure A, based on the measurement of the pressure gauge in the process line of the pressure control system and the valve for supplying the pressure B from the process line to the device (1) , and the pressure control system further comprises at least one pressure OUT valve (6) for releasing pressure from the process line based on a pressure C, which is set to a desired value being higher than the pressure A, and the control unit is arranged to control automatically the pressure valve (7) and the pressure OUT valve (6) and the pressures A, B and 0.

20. The apparatus according to claim 18, c h a r a c t e r i z e d in that the pressure control system comprises the pressure source (9) , the pressure gauge (5) for measuring pressure and the pressure valve (7) for feeding the pressure A from the pressure source and the control unit to adjust the pressure B, which is lower than the pressure A, based on the measurement of the pressure gauge in the process line of the pressure control system and the valve for supplying the pressure B from the process line to the device (1) , wherein the process line is a first line, and the pressure control system further comprises at least one check valve (8)for releasing pressure from the first line to outside, and at least one second pressure source (11) , at least one valve (17) for feeding pressure from the second pressure source to a second line of the pressure control system, at least one second pressure gauge (4) for measuring overpressure in the second line and at least one pressure OUT valve (6) for releasing pressure from the second line, and the second pressure source (11) , the valve (17) , the second pressure gauge (4) and pressure OUT valve (6) are arranged to set a pressure D to a desired value, which is higher than the pressure A, in the second line, wherein the pressure control system controls the pressures A, B and D.

21. The apparatus according to any one of claims 18 to 20, c h a r a c t e r i z e d in that the device is selected from the group consisting of a reactor, digester, bleaching tower, liquid storage, tank, pumping system, or any combination thereof.

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