Simulation-based cracker development for the propulsion system of an inland waterway vessel

In order to speed up the decar­bo­niza­tion of ship­ping, the CF08_2 project is deve­lo­ping an ammonia-powered, contai­ne­rized inland vessel propul­sion system with 350 kW propul­sion power and evalua­ting it ” on-land”. Figure 1 shows a sche­matic repre­sen­ta­tion of the propul­sion system. To improve the igni­tion and effi­cient conver­sion of the ammonia in the engine, a certain propor­tion of hydrogen is also required in the fuel. For this purpose, an ammonia cracker is connected upstream of the engine, which endo­ther­mi­cally splits a partial flow of the ammonia into hydrogen and nitrogen and feeds this mixture to the combus­tion engine as pilot fuel.

Figure 1: Sche­matic repre­sen­ta­tion of the ammonia-powered propul­sion system of an inland waterway vessel

Deve­lo­p­ment work at the ZBT

The cracker system is deve­loped, desi­gned and built by ZBT and exten­si­vely tested and opti­mized. After successful contai­ne­riza­tion of the cracker plant, ZBT also supports the coupling with the engine and the opera­tion of the entire system. The system deve­lo­p­ment is supported by ZBT’s own exten­sive simu­la­tion work, in parti­cular for process and reactor design and control deve­lo­p­ment. An over­view of the simu­la­tion work is shown in Figure 2. 0D simu­la­tion in Aspen Plus® is used for process deve­lo­p­ment. The aim here is to imple­ment opti­mized heat inte­gra­tion and deter­mine all rele­vant mate­rial and energy flows. These are required for the design and selec­tion of plant compon­ents such as the reactor, burner, heat exch­anger, compres­sors, etc. The detailed design of the reactor and flow compon­ents such as distri­butor struc­tures is carried out taking into account the reac­tion as well as mate­rial, heat and momentum exch­ange, supported by 2D/3D multi­phy­sics simu­la­tions in COMSOL Multi­phy­sics®. The 0D model from Aspen Plus® is converted into a dynamic and real-time capable model in AVL Crui­seTM M for the control deve­lo­p­ment for the auto­ma­tion of the cracker system.For this purpose, a 2D FVM model of the cracking reactor is deve­loped in Python and inte­grated into AVL using the Model.ConnectTM tool.The dynamic AVL model is used to develop opti­mized opera­ting stra­te­gies, in parti­cular for start-up and shut­down processes and load changes as well as safety-related issues.This enables not only an increase in system effi­ci­ency and safety, but also an impro­ve­ment in opera­tion under variable load and an increase in service life by, for example, avoi­ding cata­lyst overheating.

Parallel to the simu­la­tion work, an ammonia labo­ra­tory infra­struc­ture and test envi­ron­ment is curr­ently being set up at the ZBT, which will make it possible to expe­ri­men­tally examine not only the compon­ents of the cracker system indi­vi­du­ally and in the process tech­no­logy network, but also the entire cracker system. This will provide exten­sive expe­ri­mental data to vali­date the simu­la­tion work.

Figure 2: Use of simu­la­tion tools at ZBT for the deve­lo­p­ment and opti­miza­tion of the cracker system

Poten­tial analysis at LTT

In order to increase the effi­ci­ency of the overall cracker and engine system, the Chair of Tech­nical Ther­mo­dy­na­mics at the Univer­sity of Rostock is inves­ti­ga­ting the possi­bi­li­ties of ther­mally coupling the engine and cracker system at a theo­re­tical level. The engine has a waste heat poten­tial that is depen­dent on the opera­ting state. This waste heat poten­tial can be utilized in the cracker and thus reduce the cracker’s external energy requi­re­ments. This results in an increase in the effi­ci­ency of the overall system. In order to evaluate the various options and carry out opti­miza­tions, both a 0D simu­la­tion study of the overall system and a detailed 3D simu­la­tion of the heat coupling into the cracker are being carried out. Initial results of the simu­la­tion of the overall system show the possible poten­tial of heat coupling: an impro­ve­ment in system effi­ci­ency of up to 4 percen­tage points.

Results and findings from the deve­lo­p­ment work on the ammonia cracker system are commu­ni­cated on an ongoing basis within the sub-project and thus have a direct influence on the test set-ups and expe­ri­ments for the rese­arch work at KIT in Karls­ruhe and the Univer­sity of Rostock.