Türbo Kompresörlerin Kontrolü

Abstract

Bu çalışmada, günümüzde gaz taşımacılığının en önemli parçası kompresörlerden, karakteristiklerinden, kapasite kontrol yöntemlerinden, kontrol esaslarından bahsedilecek, modellenmesi ve simülasyonu ele alınacaktır. İkinci bölümde genel olarak kompresör tiplerinden, kompresör istasyonunun esaslarından, kapasite kontrol yöntemlerinden, türbo kompresörlerin karakteristiklerinden bahsedilecektir. Üçüncü bölümde ise Türbo kompresörlerin dinamik özelliklerinden Surge ve Choke olayından bahsedilecek, teknik olarak açıklanacaktır. Daha sonra en önemli dinamik özelliklerden özelliklerden olan surge ve kontrolü hakkında detaylı bilgi verilip, bir surge kontrol ifadesi ele alınacaktır. Dördüncü bölümde Paralel Çalışan Türbo Kompresörlü İstasyonların "S" kriteri ile kontrolünden bahsedilecek, Surge kontrol, Kapasite kontrol ve paralel kompresör kontrolü birlikte ele alınacaktır. Beşinci bölümde bir merkezkaç Türbo kompresörün karakteristik eğrilerinden eğri uydurma yöntemi ve gauss-eleminasyon yöntemi kullanılarak modellenmesi yapılacak daha sonra bir devre modeli yapılarak ve devre modeli esas alınarak surge kontrolle birleşik kompresör basınç kontrolünün bir algoritması oluşturulacak ve bu algoritma Gerçek bir doğal gaz kompresörün değerleri esas alınarak simülasyonu yapılacaktır. Son olarak da sonuçlar ve öneriler belirtilecektir.Today, the importance of pressure air and gas systems in every part of industry and in our daily life is very great. The natural gas, petroleum type gases and other industrial gases that provide energy to our homes and industry are pressured by means of compressors in order not to loss their energies during transport. The most important one among them is turbo compressors that can be used at very high capacities and pressures. Each turbo compressor has a special characteristic. There exist types providing fix pressure or fix capacity. In case the gas has not enough transmission energy during transportation of a gas, the necessary energy is provided by means of a compressor. To recover the pressure losses and adjust the gas flows, compressor stations are installed on some parts of lines. The types of compressor stations are classified as follows: 1. Collecting stations 2.Adjustment and main line stations 3. Re-pressuring and cyclic stations ^Regional stations for deporting The compressor stations include 3 main parts: l.Main gas system 2.Smallgas system 3. Auxiliary gas system Compressors can be examined under 3 categories: IX 1 Jet (ejector) compressors 2. Rotary type compressors a-) Rotary bellow type b-) Turbo compressors ba) centrifugal (radial) type be) axial compressors 3. Piston type compressors In the centrifugal compressor, a gas enters into a closed body and then arrives in the wings of a turbine and gains a high speed. This high speed is converted to the pressure energy in a diffuser. In praticaL, the radial compressors are used on the long pipe lines. The following expression shows the operation of a radial compressor. H = -m-Z.R.T. m-1 m-l X) -1 In control of capacities of compressors, many method can be used by considering the technical advantages and costs. These are: Compressor throttling Suction throttling Discharge throttling Inlet guide vanes (guide vane positioning) Variable rotation speed The most attractive one among them is the variable rotation speed. The compression rate established by a compressor can be related to rotation speed as follows: T^=JL.z.R.Tı. 2.g m-1 (pA m-l VPJ Controlling of the rotation speed of compressors is the most productive method. As a result of the cubic relation between speed and power, the small speed decreases provide big power savings. N2 U2> This is a conflicting aero-dynamic event frequently occurs in choke axial turbo compressors and of which results are very dangerous like surge. It is very difficult to understand their operating mechanisms. Choke can be simply defines as preventing of flow or suffocation. The way of protecting a compressor from choke is to place an anti-choke valve at outlet. Surge is an unbalance operating situation having an aerodynamic vibration caused by the back flow towards to compressor by the effect of pressure increment in the system where turbo compressor gives gas. This is a very important operation characteristic of Surge turbo compressors that can be easily recognised by their characteristic noises. Therefore, the compressor can become out of operation. The most effective way of preventing this to feedback the compressor outlet. So the necessary minimum capacity is provided and it is moved from the surge limit. Some surges are so fast that the conventional control systems can not determine them. So the records do not give any surge and when the compressor is operated many damages can occur that reduce the productivity of a compressor. For this reason it is obligatory to use very fast equipment and transmission systems, (transmitters) The eqution below is used to determine the surge event in the PI controller, bi constant provides a surge control line parallel to surge limit line. With a di constant that was determined previously, fast surges are prevented. XI *,.AP4+6, =AFg As the compressors in the compressor stations have different characteristics and capacities, the net distance from the surge control line is not useful and instead of this, S criteria performing this distance as relative is used. S criteria provides the followings: -The control of approach of all the compressors to the surge limit line at equal time. -Increases the energy productivity of station -Provides the complete control of pressure and speed -Increases the protecting of machine -Provides the development of automation The following circuit model is formed in controlling of a compressor: Surge control valve fronsurge controller Gas Cooler frpn f' pressure controller Conpress ?<4 Q, |to pressure controller <§>-- both corvEröTler Rotenetre AP8 As the modelling of compressors, by means of the variable rotation speed control is taken as a base, characteristic curves of compresspor, H=f(n,Q) performing pressure work becoming equal to inlet capacity of Qg at various rotation speeds are taken into consideration. Accordingly, the 2. degree polynomial equality is found. Then with this equality, a numeric model is obtained from the Coberra 6556 model of Cooper company. xn 2\ r&, H = (Ao + A,.n + A2.nz) + (B0 + Bi.n + B2.nz)Q + (Co + Ci.n + C2.nz)Q (kJ/kg) The above circuit will be used in the compressor control model including the numeric model and surge control of Coberra 6556 model compressor produced by the Cooper company. So while the compressor going on its main duty of pressuring it will be also protected from surge. The control algorithm providing the working of this circuit is as follows. It controls the rotation speed and surge control valve of compressor while the inlet capacity is changing and protects the compressor from surge. For this purpose, a digital PID controller to keep the outlet pressure fix and a digital PI controller to protect the compressor from surge are used. Pressure control xni A computer program related to the solution of this algorithm is made at Matlab. Accordingly, its changing while reaching to outlet pressure set point at high- low rotations above the surge capacity limit (with high and little controller gains) and then its changing while reaching to outlet pressure set point at high-low rotations below the surge capacity limit are observed. Results show that, the application of high gaining to the pressure controller cause high pressure values during the provisional reply of outlet pressure. This is an unacceptable situation and low controller gaining is more suitable with regard to security. On the other hand, when it is reached to the below of surge capacity, There occurs more waving in the low rotation speeds than the high rotation speeds.