NOVELTY - A system for biodiesel production comprises: heat exchanger (108) including first lumen and second lumen helically intertwined about axis; and reactor (112) including sintered plug in vessel in fluid communication with first pipe and second pipe, where plug has pores of at least 0.01 mu m diameter and is configured to catalyze reaction.    USE - As system, conduit and reactor for biodiesel production (all claimed).    ADVANTAGE - The system for biodiesel formation includes heat exchanger and reactor. The heat exchanger can conserve thermal energy by extracting otherwise discarded thermal energy from reaction product stream. The reactor can synthesize biodiesel at supercritical reaction conditions. The system can operate at supercritical processing conditions i.e. at temperature or pressure above critical point of reaction mixture, such as super critical condition includes pressure of 8.3-35 MPa. Operating at such temperature and pressures can homogenize reactants, such as contents in heated reaction mixture conduit, and brings lipid and alcohol molecules into proximity. Energy costs of synthesizing biodiesel via supercritical reaction conditions can be similar or less than that of typical catalytic biodiesel production. The reactor can convert free fatty acids to esters instead of soap, further reducing waste and post-reaction processing. The contents of pressure regulated reaction product conduit can be at atmospheric pressure and fed to separator. The separator can separate excess alcohol in reaction product from biodiesel or various byproducts. Further system can be transportable i.e. can be transported by light motor vehicle (e.g. vehicle smaller than commercial semi-truck). The system can be separated into number of discrete subsections, further lending system to transportability. Each subsection can fit through standard doorway or stack for ease of transportability.    DETAILED DESCRIPTION - A system for biodiesel production comprise: heat exchanger (108) including first lumen and second lumen helically intertwined about axis; and reactor (112) including sintered plug in vessel in fluid communication with first pipe and second pipe, where plug has pores of at least 0.01 mu m diameter and is configured to catalyze reaction. The reactor is configured to operate at up to 500 degrees C, and at pressure of at least 8.3 megapascals (MPa). The system includes heater that is in fluid communication with first pipe and configured to add thermal energy to system. The system is configured to be transportable. The sintered plug includes stainless steel. INDEPENDENT CLAIMS are included for the following:    (1) conduit, comprising first lumen and second lumen, where first lumen is configured to carry first fluid in first direction and second lumen is configured to carry second fluid in second direction, first lumen is helically twisted relative to second lumen, and second lumen is configured to conductively transfer thermal energy to first lumen for substantial portion of length of conduit;    (2) reactor, comprising: shell having input port configured to receive reaction mixture and output port configured to discharge reaction product; and sintered plug within shell, where sintered plug has first catalyst, first catalyst is configured to transform reaction mixture into reaction product, and plug has pores of at least 0.01 mu m diameter; and    (3) method for biodiesel production, involving: providing reaction mixture to heat exchanger, reaction mixture including lipid and alcohol; pre-heating reaction mixture in heat exchanger, where heat exchanger includes first pipe including reaction mixture, first pipe is helically intertwined about axis with second pipe, and second pipe including reaction product of biodiesel reaction; and reacting reaction mixture in reactor supercritical condition to produce reaction product, where reactor includes sintered plug in vessel fluidly coupled to first pipe and to second pipe, where plug has pores of at least 0.01 mu m diameter and plug is configured to catalyze reaction.    DESCRIPTION OF DRAWING(S) - The figure shows system for producing biodiesel.    Lipid input tank (102)    Alcohol input tank (104)    Heat exchanger (108)    Reactor (112)    Storage tank (118)