A new Eulerian-Lagrangian pyrolysis model is developed in the thermally thick regime to study the pyrolysis yields of large biomass particles based on a multistep kinetic scheme. The integrated pyrolysis model is first validated with experiments of centimeter-sized wood particles under both low- and high-temperature conditions. Good agreement is obtained between simulations and experimental measurements for low-temperature (375 and 470 degrees C) pyrolysis. However, for 800 degrees C pyrolysis, the predicted char, tar, and gas yields are not as accurately predicted as those of the low-temperature situation, while the overall gas and tar yields show an improvement when secondary tar decomposition is considered. Moreover, simulation results reveal that different sized particles generate similar char, tar, and gas yields, which account for about 30, 52, and 12% of the initial mass, respectively. Besides, a significant increase of the gas yield (similar to 70%) and a moderate decrease of the char yield (similar to 25%) are observed when the pyrolysis temperature increases from 400 to 700 degrees C, while the tar yield only changes slightly with first an increasing trend and then a decreasing trend with raising the pyrolysis temperature. The biomass type also has an important impact on both light gas and tar yields as a result of different components in each particle. Finally, effects of tar cracking and alkali metal catalyst on pyrolysis are also discussed.