One challenge for the simulation and optimization of real gas pipe networks is the treatment of compressors. Their behavior is usually described by characteristic diagrams reflecting the connection of the volumetric flow and the enthalpy change or shaft torque. Such models are commonly used for an optimal control of compressors and compressor stations [4,7] using stationary models for the gas flow through the pipes. For transient simulations of gas networks, simplified compressor models have been studied in [1][2][3]. Here, we present a transient simulation of gas pipe networks with characteristic diagram models of compressors using a stable network formulation as (partial) differential-algebraic system. Let G = (V, E) a directed graph with vertices V = V + ∪ V − and edges E = E P ∪ E C where V − and V + are the nodes where gas can enter and exit the network respectively and E P and E C being the set of pipes and compressors respectively. In addition we define the sets δ − (u) and δ + (u) as the set of edges that are directed towards and away from node u ∈ V respectively.Theorem 1.1 Let G = (V, E) be a connected, directed graph that describes a gas network with pipes and compressors and letThen it holds, that the pipes can be directed in a way that
Pipe ModelingWe model pipes by a simplification of the isothermal Euler equations [2] ∂ t p e + c 2 a e ∂ x q e = 0, ∂ t q e + a e ∂ x p e = − λ e c 2 2D e a e q e |q e | p e − ga e h e c 2 p e , e ∈ E P (1) on [0, T ] × [0, e ] where p and q are the pressure and mass flow along pipe e, a e is the cross-sectional area, D e the diameter, λ e the friction factor, g the gravitational acceleration, h e the elevation of the pipe, c is the speed of sound, e the length of the pipe. Also we identify the point x = 0 with the position at the node u and x = e with node v for e = (u, v). Such a modeling is known to describe the gas flow through a pipe sufficiently well if the velocity of the gas is much less than the speed of sound which is usually the case for real gas transport networks.
Compressor ModelingFor the compressor model we consider the characteristic diagram model for turbo-compressors describing the relation between the adiabatic enthalpy and the volumetric flow rate [4,7].Here H e is the adiabatic enthalpy, Q the volumetric flow rate, q e the massflow and n e the speed. Ψ e (Q, n) =Q T e A ene with A e ∈ R 3×3Q e = (1, Q e , Q 2 e ) andn e = (1, n e , n 2 e ) . The fourth equation of (2) determines the control of the compressor. We model the entry-nodes as a boundary condition for the pressure, leading to p e (t, 0) = p Γ u (t) for e ∈ δ + (u), u ∈ V + . For the nodes u ∈ V − we model the coupling by balance equations for the massflows e P ∈δ − (u) q e P (t, e P ) − e P ∈δ + (u) q e P (t, 0) + e C ∈δ − (u) q e C (t) − e C ∈δ + (u) q e C (t) = q Γ u (t)