In this work, a systematic approach combining different energy solutions and the time-varying energy demands is used to identify the operating conditions and arrangements for industrial complexes. A kraft pulp mill integrated to an urban district heating network is used as case study. The recuperative boiler is replaced by a black liquor gasification system integrated to a methanation system aiming to produce synthetic natural gas. In view of the seasonal energy costs, other technologies are also assessed including power-to-gas systems, carbon capture systems, CO2 injection and liquid storage, which helps offsetting the intermittency of renewable resources. A district heating network using CO2 as a heat transfer fluid is considered for the energy system supply of a city. The methane stored in liquid form is used in the winter to balance the electrical needs by the integrated system. The implementation of CO2 management and synthetic natural gas storage can ensure consistent operations even during the strained periods of the electricity grid. Additionally, injecting biogenic CO2 emissions and receiving credits for it can help offset the costs associated with adopting these new technologies.